What is alg.exe?

1)It is a process belonging to Microsoft Windows Operating System.
2)It is a core process for Microsoft Windows Internet Connection sharing and Internet connection firewall.
3)This program is important for the stable and secure running of your computer and should not be terminated.
4)Application Layer Gateway Service (alg)
5)Application Layer Gateway service is a component of of Windows OS. It is required if you use a 3rd party firewall or Internet Connection Sharing (ICS) to connect to the internet. Do not end this program in task manager - you will lose all internet connectivity until next restart or login.

LOCATION: The alg.exe file is located in the folder C:\Windows\System32. In other cases, alg.exe is a virus, spyware, trojan or worm! Check this with Security Task Manager.

Windows errors related to svchost.exe ?

1)svchost.exe is a system process belonging to the Microsoft Windows Operating System which handles processes executed from DLLs.
2)This program is important for the stable and secure running of your computer and should not be terminated.
3) svchost.exe is a process registered as a backdoor vulnerability which may be installed for malicious purposes by an attacker allowing access to your computer from remote locations, stealing passwords, Internet banking and personal data.

4)It is a process which is registered as a trojan. This Trojan allows attackers to access your computer from remote locations, stealing passwords, Internet banking and personal data. This process is a security risk and should be removed from your system.

5)It is a process belonging to Microsoft Service Host Process. This could also be a stealth monitoring software that sits in the background and tracks all activities such as keyboard input (including websites visited, passwords etc.) This information can be sent to third parties through email or ftp uploads. If you did not intentionally install this program make sure you remove it to protect your privacy.

Determining whether svchost.exe is a virus or a legitimate Windows process depends on the directory location it executes or runs from

What is Svshost.exe?

svshost.exe - svshost - Process Information
Process Name: Worm.P2P.Spybot.gen virus

Windows errors related to svshost.exe ?

svshost.exe is a process which is registered as Worm.P2P.Spybot.gen virus. This Trojan spreads on normally P2P sharing tools and, spreads locally via network shares. This process is a security risk and should be removed from your system.

when does Orkut is banned appears?

When we open the site www.orkut.com

the message Orkut is banned...you fool!! appears

This is caused due to a virus Heap41a.
This is removed by using Task manager ( CTRL+ALT+DEl)

press the tab processes

if in that a process named svchost.exe is running with the user name , then remove it by doing end task


if the site is blocked :
goto www.hidemyass.com and type the url (www.orkut.com) there and it ll open.

2. Click start->run->regedit
3. press ctrl + f and type "heap32a"
4. delete all values by this name.
5. close regedit and open "My Computer"
6. in the address bar type "c:\Heap32a"
7. press ctrl + A and shift + del all the items.

Using the Syspart Method to Preinstall WindowsWhen

Using the Syspart Method to Preinstall Windows
When you use the Syspart method, you stop the installation of Windows after the file-copy phase of Setup, duplicate the hard disk, and then complete Windows Setup on each destination computer built from the duplicate hard disks. For more information on the Setup process, see Stages of Windows Setup.

The Syspart method does take less time than running Winnt32.exe on every computer. However, because both the text-mode and GUI-mode phases of Setup must run on each destination computer, this legacy technique is more time-consuming than duplicating a fully installed version of Windows onto one or more destination computers, as described in Creating a Master Installation and Placing the Base Operating System on the Destination Computers.

Use two hard disks, with a primary partition on the clean, newly formatted destination hard disk. The destination hard disk does not need to be physically installed in the master computer; instead, you can access the destination hard disk through a network connection.

Important

Winnt.exe does not have the Syspart command-line option. You must use Winnt32.exe.
Run the winnt32 /sysprep command from a computer already running Windows 2000, Windows XP Home Edition, Windows XP Professional, or Windows 2002 Server. You cannot use this command-line option on Windows 95, Windows 98, Windows Millennium Edition, or 64-bit editions of Windows.
To create a hardware-independent snapshot of Windows files

Choose a computer to use as the master computer. The master computer must use Windows NT, Windows 2000, Windows XP Home Edition, Windows XP Professional, or Windows 2002 Server.
Start the master computer and connect to the preinstallation distribution folder.
Start Windows Setup, and then click Start, click Run, and then type:
Winnt32 /Unattend:Unattend.txt /s:install_source /Syspart:system_drive2 /tempdrive:system_drive2

where:

Unattend.txt
Specifies the answer file used for unattended Setup. It provides answers to some or all of the prompts the end user normally responds to during Setup. Using an answer file is optional when creating the master installation.
install_source
Specifies the location of the Windows files. You can specify multiple /s options if you want to install from multiple sources simultaneously.
system_drive2
Specifies the system partition of a second hard disk on which you preinstall Windows and applications.
Because the /syspart and /tempdrive options reference the same drive, Windows is installed on the primary partition of a that hard disk.

Important

The /syspart option for Winnt32.exe is only run from a computer already running Windows 2000, Windows XP Home Edition, Windows XP Professional, or Windows 2002 Server. You cannot use this command-line option on Windows 95, Windows 98, Windows Millennium Edition, or 64-bit editions of Windows.
If you use the /tempdrive option, make sure you have sufficient free disk space on your second drive to install both Windows and your applications.
After Setup copies files to the hard disk, shut down the computer.
Remove the hard disk from the computer, and then use disk-duplicating equipment or software to make copies of the hard disk.
Install a duplicated hard disk into a destination computer.
Start the destination computer and complete Windows Setup.
Run Sysprep, with the -nosidgen option, to prepare the computer for the end user.
For more information about Sysprep, see Using Sysprep.

You can also use the Syspart method to create a master installation to duplicate onto computers that use a different hardware abstraction layer (HAL).

To create a HAL-specific snapshot of Windows files

Create a source disk using the Syspart method to copy files.
Make enough copies of this disk to configure and use as the master installation(s) for each type of computer you preinstall in your factory.
For each type of computer, place a source disk into the hardware-specific "master computer". Turn on the computer.
Windows Setup completes automatically.

When Setup is complete, run Sysprep to prepare the computer for the end user.
Duplicate the hardware-specific hard disk and install the each duplicate in a computer identical to the master computer.

MCSE sample question

The SYSPART process can be initiated on a computer running which of the following?
a. Windows 95
b. Windows 98
c. Windows NT
d. Windows 2000
e. all of the above


A) a & C

Microsoft Windows 2000 Guide to Unattended Setup

Microsoft Windows 2000 Guide to Unattended Setup
Answer File Parameters for Unattended Installation of the Windows 2000 Family of Operating Systems

Unattended Setup mode is a hands-free method of installing Microsoft® Windows® 2000 that is convenient for Original Equipment Manufacturers (OEMs), Administrators in corporations, Value Added Resellers (VARs), and other users.

Note: For a complete listing of Winnt.exe and Winnt32.exe commands, see Windows 2000 Help. Or, at a command prompt, switch to the \i386 folder on the Windows 2000 product CD, and then type: winnt /? or winnt32 /?

• To start Windows 2000 Setup in unattended Setup mode from MS-DOS® or Windows 3.1/Windows for Workgroups, a user must specify:

winnt /u: /s: /t:


• To start Windows 2000 Setup in unattended Setup mode from Windows 95 or Windows 98, Windows NT®, or Windows 2000, a user must specify:

winnt32 /unattend: /s:
[/syspart:] [/tempdrive:]



where:

• is a file that contains answers to questions that should be automated during installation.

• is the location of the Windows 2000 installation files.

• /syspart copies all boot files to the target drive and marks it as active. This option is only valid for Winnt32.exe.

• /tempdrive copies all the installation files to a temporary folder on the target drive. This option implies that Windows 2000 must be installed in the specified drive and is only valid for Winnt32.exe.

If the temporary folder is full, the user is prompted to choose another directory during setup. After this is done, unattended setup continues.

Note: The /tempdrive parameter, like the /t switch for the Winnt.exe command, is useful to ensure the correct drive is chosen without user intervention when the hard disk has multiple partitions or hard disks.

• /t (Optional) copies all the installation files to a temporary directory on the target drive. This option assumes that Windows 2000 is installed in the specified drive and is only valid for Winnt.exe.

If the temporary directory is full, the user is prompted to choose another directory during setup. After this is done, unattended setup continues.

Note: Use the /t or /tempdrive switches to install Windows 2000 to a partition other than the boot partition on a computer.


A combination of /syspart and /tempdrive is useful if the target drive is used as the primary drive on another computer. The /syspart and /tempdrive parameters are optional. By using them together, you can create a custom image that can be used across non-identical computers. GUI-mode Setup then completes the installation on those computers.

Important: If you direct /syspart to a non-boot drive on your computer, remove that drive before restarting your computer. Otherwise, your computer cannot boot.

To start Windows 2000 Setup in unattended Setup mode from the Windows 2000 product CD

1.
The computer must support booting from the CD-ROM drive—El Torito No Emulation CD boot support.

2.
The answer file must be named Winnt.sif and must be placed on a floppy disk to be inserted as soon as the computer boots from the CD.

The Winnt.sif answer file may also be placed on and run from a bootable CD. For more information about creating a bootable CD, see KB article 167685, "How to Create an El Torito Bootable CD-ROM" at the Microsoft Product Support Services Web site:

http://support.microsoft.com/support/

3.
The answer file must contain a [Data] section with the required keys specified. For more information, see "[Data]," later in this document.


Note: When using the Remote Installation Service (RIS) to install Windows 2000 on a computer that has a bootable network card, specify the network card as the first bootable device and demote all others. You then provide the maximum possible number of methods for successfully deploying Windows 2000 to computers in your environment. For more information about using RIS, see "[RemoteInstall]," later in this document.

One method to simplify this process is to modify the BIOS to specify the CD-ROM as the first bootable device, the floppy drive as the second, and the hard drive as the third.



Answer File Format
In general, an answer file, such as Unattend.txt or Sysprep.inf, consists of section headers/keys, parameters, and the values for each parameter. Most of the section headers are pre-defined, but some may be user-defined. You don't need to specify all of the possible parameters in the Unattend.txt file if the installation does not require them.

The file format is as follows:

[section1]
;
; Section contains keys and the corresponding
; values for those keys/parameters.
; keys and values are separated by '=' signs
; Values that have spaces in them usually require double quotes
; "" around them
;
key = value
.
.
[section2]
key = value

Invalid parameter values generate errors or may cause incorrect behavior after setup.

Top of page
Description of Answer File Parameters
Bold
for a section or a key name. The exact name specified must be used.


for a key or a section name when specified and enclosed in brackets (< >) and italicized. The name used can be specified by the creator of the answer file.

Key values
are string type, unless otherwise mentioned. Wherever Type = Numeric is specified, the value is written as a decimal number unless expressly mentioned otherwise.

Optional
indicates that the key is optional. Unless indicated, all keys are required for the given section.

Default
indicates the default value assumed if a key is not present.

difference between microsoft windows 2003 & 2000

Q. How is Microsoft Windows Server 2003 different from Microsoft Windows 2000?
A. The Microsoft Windows Server 2003 family takes the best of Microsoft Windows 2000 Server technology and makes it easier to deploy, manage, and use. For more information, see the Microsoft Windows Server 2003 Web site.

More Information( FAT, NTFS)

MORE INFORMATION

FAT OVERVIEW :

FAT is by far the most simplistic of the file systems supported by Windows NT.
File allocation table (FAT), which is really a table that resides at the very "top" of the volume.

*To protect the volume, two copies of the FAT are kept in case one becomes damaged. In addition, the FAT tables and the root directory must be stored in a fixed location so that the system's boot files can be correctly located.
*A disk formatted with FAT is allocated in clusters, whose size are determined by the size of the volume. When a file is created, an entry is created in the directory and the first cluster number containing data is established. This entry in the FAT table either indicates that this is the last cluster of the file, or points to the next cluster.
*Updating the FAT table is very important as well as time consuming. If the FAT table is not regularly updated, it can lead to data loss. It is time consuming because the disk read heads must be repositioned to the drive's logical track zero each time the FAT table is updated.
* There is no organization to the FAT directory structure, and files are given the first open location on the drive. In addition, FAT supports only read-only, hidden, system, and archive file attributes.

*****************************************************************************************
ing Convention

FAT uses the traditional 8.3 file naming convention and all filenames must be created with the ASCII character set.
*The name of a file or directory can be up to eight characters long, then a period (.) separator, and up to a three character extension. The name must start with either a letter or number and can contain any characters except for the following: . " / \ [ ] : ; = ,
If any of these characters are used, unexpected results may occur. The name cannot contain any spaces. The following names are reserved: CON, AUX, COM1, COM2, COM3, COM4, LPT1, LPT2, LPT3, PRN, NUL
All characters will be converted to uppercase.
**************************************************************************************

Advantages of FAT

It is not possible to perform an undelete under Windows NT on any of the supported file systems. Undelete utilities try to directly access the hardware, which cannot be done under Windows NT. However, if the file was located on a FAT partition, and the system is restarted under MS-DOS, the file can be undeleted. The FAT file system is best for drives and/or partitions under approximately 200 MB, because FAT starts out with very little overhead. For further discussion of FAT advantages, see the following:

*******************************************************************************************
Disadvantages of FAT


*when using drives or partitions of over 200 MB the FAT file system should not be used.
*This is because as the size of the volume increases, performance with FAT will quickly decrease. It is not possible to set permissions on files that are FAT partitions.
* FAT partitions are limited in size to a maximum of 4 Gigabytes (GB) under Windows NT and 2 GB in MS-DOS. For additional information on this limitation, please see the following article in the Microsoft Knowledge Base:


•**************************************************************************************

HPFS OVERVIEW

The HPFS file system was first introduced with OS/2 1.2 to allow for greater access to the larger hard drives

* HPFS maintains the directory organization of FAT, but adds automatic sorting of the directory based on filenames. Filenames are extended to up to 254 double byte characters.
*Allows a file to be composed of "data" and special attributes to allow for increased flexibility in terms of supporting other naming conventions and security.
*The unit of allocation is changed from clusters to physical sectors (512 bytes), which reduces lost disk space. Under HPFS, directory entries hold more information than under FAT. As well as the attribute file, this includes information about the modification, creation, and access date and times. Instead of pointing to the first cluster of the file, the directory entries under HPFS point to the FNODE. The FNODE can contain the file's data, or pointers that may point to the file's data or to other structures that will eventually point to the file's data. HPFS attempts to allocate as much of a file in contiguous sectors as possible. This is done in order to increase speed when doing sequential processing of a file. HPFS organizes a drive into a series of 8 MB bands, and whenever possible a file is contained within one of these bands. Between each of these bands are 2K allocation bitmaps, which keep track of which sectors within a band have and have not been allocated. Banding increases performance because the drive head does not have to return to the logical top (typically cylinder 0) of the disk, but to the nearest band allocation bitmap to determine where a file is to be stored. Additionally, HPFS includes a couple of unique special data objects:

*******************************************************************************************************
Super Block

The Super Block is located in logical sector 16 and contains a pointer to the FNODE of the root directory. One of the biggest dangers of using HPFS is that if the Super Block is lost or corrupted due to a bad sector, so are the contents of the partition, even if the rest of the drive is fine. It would be possible to recover the data on the drive by copying everything to another drive with a good sector 16 and rebuilding the Super Block. However, this is a very complex task.

*******************************************************************************************
Spare Block
loadTOCNode(2, 'moreinformation');
The Spare Block is located in logical sector 17 and contains a table of "hot fixes" and the Spare Directory Block. Under HPFS, when a bad sector is detected, the "hot fixes" entry is used to logically point to an existing good sector in place of the bad sector. This technique for handling write errors is known as hot fixing. Hot fixing is a technique where if an error occurs because of a bad sector, the file system moves the information to a different sector and marks the original sector as bad. This is all done transparent to any applications that are performing disk I/O (that is, the application never knows that there were any problems with the hard drive). Using a file system that supports hot fixing will eliminate error messages such as the FAT "Abort, Retry, or Fail?" error message that occurs when a bad sector is encountered. Note: The version of HPFS that is included with Windows NT does not support hot fixing.

Advantages of HPFS
loadTOCNode(2, 'moreinformation');
HPFS is best for drives in the 200-400 MB range. For more discussion of the advantages of HPFS, see the following:
•

**************************************************************************************
Disadvantages of HPFS
loadTOCNode(2, 'moreinformation');
Because of the overhead involved in HPFS, it is not a very efficient choice for a volume of under approximately 200 MB. In addition, with volumes larger than about 400 MB, there will be some performance degradation. You cannot set security on HPFS under Windows NT. HPFS is only supported under Windows NT versions 3.1, 3.5, and 3.51. Windows NT 4.0 cannot access HPFS partitions. For additional disadvantages of HPFS, see the following:
•*************************************************************************************
NTFS OVERVIEW

From a user's point of view, NTFS continues to organize files into directories, which, like HPFS, are sorted. However, unlike FAT or HPFS, there are no "special" objects on the disk and there is no dependence on the underlying hardware, such as 512 byte sectors. In addition, there are no special locations on the disk, such as FAT tables or HPFS Super Blocks. The goals of NTFS are to provide:
•
Reliability, which is especially desirable for high end systems and file servers
•
A platform for added functionality
•
Support POSIX requirements
•
Removal of the limitations of the FAT and HPFS file systems

Reliability

To ensure reliability of NTFS, three major areas were addressed: recoverability, removal of fatal single sector failures, and hot fixing. NTFS is a recoverable file system because it keeps track of transactions against the file system. When a CHKDSK is performed on FAT or HPFS, the consistency of pointers within the directory, allocation, and file tables is being checked. Under NTFS, a log of transactions against these components is maintained so that CHKDSK need only roll back transactions to the last commit point in order to recover consistency within the file system. Under FAT or HPFS, if a sector that is the location of one of the file system's special objects fails, then a single sector failure will occur. NTFS avoids this in two ways: first, by not using special objects on the disk and tracking and protecting all objects that are on the disk. Secondly, under NTFS, multiple copies (the number depends on the volume size) of the Master File Table are kept. Similar to OS/2 versions of HPFS, NTFS supports hot fixing.
***********************************************************************************
Added Functionality
One of the major design goals of Windows NT at every level is to provide a platform that can be added to and built upon, and NTFS is no exception. NTFS provides a rich and flexible platform for other file systems to be able to use. In addition, NTFS fully supports the Windows NT security model and supports multiple data streams. No longer is a data file a single stream of data. Finally, under NTFS, a user can add his or her own user-defined attributes to a file.

POSIX Support

NTFS is the most POSIX.1 compliant of the supported file systems because it supports the following POSIX.1 requirements: Case Sensitive Naming: Under POSIX, README.TXT, Readme.txt, and readme.txt are all different files. Additional Time Stamp: The additional time stamp supplies the time at which the file was last accessed. Hard Links: A hard link is when two different filenames, which can be located in different directories, point to the same data.

Removing Limitations

First, NTFS has greatly increased the size of files and volumes, so that they can now be up to 2^64 bytes (16 exabytes or 18,446,744,073,709,551,616 bytes). NTFS has also returned to the FAT concept of clusters in order to avoid HPFS problem of a fixed sector size. This was done because Windows NT is a portable operating system and different disk technology is likely to be encountered at some point. Therefore, 512 bytes per sector was viewed as having a large possibility of not always being a good fit for the allocation. This was accomplished by allowing the cluster to be defined as multiples of the hardware's natural allocation size. Finally, in NTFS all filenames are Unicode based, and 8.3 filenames are kept along with long filenames.

Advantages of NTFS

NTFS is best for use on volumes of about 400 MB or more. This is because performance does not degrade under NTFS, as it does under FAT, with larger volume sizes. The recoverability designed into NTFS is such that a user should never have to run any sort of disk repair utility on an NTFS partition. For additional advantages of NTFS, see the following:

Disadvantages of NTFS

It is not recommended to use NTFS on a volume that is smaller than approximately 400 MB, because of the amount of space overhead involved in NTFS. This space overhead is in the form of NTFS system files that typically use at least 4 MB of drive space on a 100 MB partition. Currently, there is no file encryption built into NTFS. Therefore, someone can boot under MS-DOS, or another operating system, and use a low-level disk editing utility to view data stored on an NTFS volume. It is not possible to format a floppy disk with the NTFS file system; Windows NT formats all floppy disks with the FAT file system because the overhead involved in NTFS will not fit onto a floppy disk. For further discussion of NTFS disadvantages, see the following:
•
NTFS Naming Conventions

File and directory names can be up to 255 characters long, including any extensions. Names preserve case, but are not case sensitive. NTFS makes no distinction of filenames based on case. Names can contain any characters except for the following: ? " / \ < > * :

Currently, from the command line, you can only create file names of up to 253 characters.NOTE: Underlying hardware limitations may impose additional partition size limitations in any file system. Particularly, a boot partition can be only 7.8 GB in size, and there is a 2-terabyte limitation in the partition table. For more information about the supported file systems for Windows NT, please see the Windows NT Resource Kit.

File System( NTFS ,FAT)

In computing, a file system (often also written as filesystem) is a method for storing and organizing computer files and the data they contain to make it easy to find and access them. File systems may use a data storage device such as a hard disk or CD-ROM and involve maintaining the physical location of the files, they might provide access to data on a file server by acting as clients for a network protocol (e.g., NFS, SMB, or 9P clients), or they may be virtual and exist only as an access method for virtual data (e.g., procfs).
More formally, a file system is a set of abstract data types that are implemented for the storage, hierarchical organization, manipulation, navigation, access, and retrieval of data. File systems share much in common with database technology, but it is debatable whether a file system can be classified as a special-purpose database (DBMS).[citation needed]
The most familiar file systems make use of an underlying data storage device that offers access to an array of fixed-size blocks, sometimes called sector, generally 512 bytes each. The file system software is responsible for organizing these sectors into files and directories, and keeping track of which sectors belong to which file and which are not being used. Most file systems address data in fixed-sized units called "clusters" or "blocks" which contain a certain number of disk sectors (usually 1-64). This is the smallest logical amount of disk space that can be allocated to hold a file.
However, file systems need not make use of a storage device at all. A file system can be used to organize and represent access to any data, whether it be stored or dynamically generated (eg, from a network connection).
Whether the file system has an underlying storage device or not, file systems typically have directories which associate file names with files, usually by connecting the file name to an index into a file allocation table of some sort, such as the FAT in an MS-DOS file system, or an inode in a Unix-like file system. Directory structures may be flat, or allow hierarchies where directories may contain subdirectories. In some file systems, file names are structured, with special syntax for filename extensions and version numbers. In others, file names are simple strings, and per-file metadata is stored elsewhere.
Other bookkeeping information is typically associated with each file within a file system. The length of the data contained in a file may be stored as the number of blocks allocated for the file or as an exact byte count. The time that the file was last modified may be stored as the file's timestamp. Some file systems also store the file creation time, the time it was last accessed, and the time that the file's meta-data was changed. (Note that many early PC operating systems did not keep track of file times.) Other information can include the file's device type (e.g., block, character, socket, subdirectory, etc.), its owner user-ID and group-ID, and its access permission settings (e.g., whether the file is read-only, executable, etc.).
The hierarchical file system was an early research interest of Dennis Ritchie of Unix fame; previous implementations were restricted to only a few levels, notably the IBM implementations, even of their early databases like IMS. After the success of Unix, Ritchie extended the file system concept to every object in his later operating system developments, such as Plan 9 and Inferno.
Traditional file systems offer facilities to create, move and delete both files and directories. They lack facilities to create additional links to a directory (hard links in Unix), rename parent links (".." in Unix-like OS), and create bidirectional links to files.
Traditional file systems also offer facilities to truncate, append to, create, move, delete and in-place modify files. They do not offer facilities to prepend to or truncate from the beginning of a file, let alone arbitrary insertion into or deletion from a file. The operations provided are highly asymmetric and lack the generality to be useful in unexpected contexts. For example, interprocess pipes in Unix have to be implemented outside of the file system because the pipes concept does not offer truncation from the beginning of files.
Secure access to basic file system operations can be based on a scheme of access control lists or capabilities. Research has shown access control lists to be difficult to secure properly, which is why research operating systems tend to use capabilities. Commercial file systems still use access control lists. see: secure computing
Arbitrary attributes can be associated on advanced file systems, such as XFS, ext2/ext3, some versions of UFS, and HFS+, using extended file attributes. This feature is implemented in the kernels of Linux, FreeBSD and Mac OS X operating systems, and allows metadata to be associated with the file at the file system level. This, for example, could be the author of a document, the character encoding of a plain-text document, or a checksum.

[edit] Types of file systems
File system types can be classified into disk file systems, network file systems and special purpose file systems.

[edit] Disk file systems
A disk file system is a file system designed for the storage of files on a data storage device, most commonly a disk drive, which might be directly or indirectly connected to the computer. Examples of disk file systems include FAT, FAT32, NTFS, HFS and HFS+, ext2, ext3, ISO 9660, ODS-5, and UDF. Some disk file systems are journaling file systems or versioning file systems.

[edit] Flash file systems
A flash file system is a file system designed for storing files on flash memory devices. These are becoming more prevalent as the number of mobile devices is increasing, and the capacity of flash memories catches up with hard drives.
While a block device layer can emulate a disk drive so that a disk file system can be used on a flash device, this is suboptimal for several reasons:
Erasing blocks: Flash memory blocks have to be explicitly erased before they can be written to. The time taken to erase blocks can be significant, thus it is beneficial to erase unused blocks while the device is idle.
Random access: Disk file systems are optimized to avoid disk seeks whenever possible, due to the high cost of seeking. Flash memory devices impose no seek latency.
Wear levelling: Flash memory devices tend to wear out when a single block is repeatedly overwritten; flash file systems are designed to spread out writes evenly.
Log-structured file systems have all the desirable properties for a flash file system. Such file systems include JFFS2 and YAFFS.

[edit] Database file systems
A new concept for file management is the concept of a database-based file system. Instead of, or in addition to, hierarchical structured management, files are identified by their characteristics, like type of file, topic, author, or similar metadata. Example: dbfs.

[edit] Transactional file systems
Each disk operation may involve changes to a number of different files and disk structures. In many cases, these changes are related, meaning that it is important that they all be executed at the same time. Take for example a bank sending another bank some money electronically. The bank's computer will "send" the transfer instruction to the other bank and also update its own records to indicate the transfer has occurred. If for some reason the computer crashes before it has had a chance to update its own records, then on reset, there will be no record of the transfer but the bank will be missing some money.
Transaction processing introduces the guarantee that at any point while it is running, a transaction can either be finished completely or reverted completely (though not necessarily both at any given point). This means that if there is a crash or power failure, after recovery, the stored state will be consistent. (Either the money will be transferred or it will not be transferred, but it won't ever go missing "in transit".)
This type of file system is designed to be fault tolerant, but may incur additional overhead to do so.
Journaling file systems are one technique used to introduce transaction-level consistency to filesystem structures.

[edit] Network file systems
Main article: Network file system
A network file system is a file system that acts as a client for a remote file access protocol, providing access to files on a server. Examples of network file systems include clients for the NFS, SMB protocols, and file-system-like clients for FTP and WebDAV.

[edit] Special purpose file systems
A special purpose file system is basically any file system that is not a disk file system or network file system. This includes systems where the files are arranged dynamically by software, intended for such purposes as communication between computer processes or temporary file space.
Special purpose file systems are most commonly used by file-centric operating systems such as Unix. Examples include the procfs (/proc) file system used by some Unix variants, which grants access to information about processes and other operating system features.
Deep space science exploration craft, like Voyager I & II used digital tape based special file systems. Most modern space exploration craft like Cassini-Huygens used Real-time operating system file systems or RTOS influenced file systems. The Mars Rovers are one such example of an RTOS file system, important in this case because they are implemented in flash memory.

[edit] File systems and operating systems
Most operating systems provide a file system, as a file system is an integral part of any modern operating system. Early microcomputer operating systems' only real task was file management — a fact reflected in their names (see DOS). Some early operating systems had a separate component for handling file systems which was called a disk operating system. On some microcomputers, the disk operating system was loaded separately from the rest of the operating system. On early operating systems, there was usually support for only one, native, unnamed file system; for example, CP/M supports only its own file system, which might be called "CP/M file system" if needed, but which didn't bear any official name at all.
Because of this, there needs to be an interface provided by the operating system software between the user and the file system. This interface can be textual (such as provided by a command line interface, such as the Unix shell, or OpenVMS DCL) or graphical (such as provided by a graphical user interface, such as file browsers). If graphical, the metaphor of the folder, containing documents, other files, and nested folders is often used (see also: directory and folder).

[edit] Flat file systems
In a flat file system, there are no subdirectories—everything is stored at the same (root) level on the media, be it a hard disk, floppy disk, etc. While simple, this system rapidly becomes inefficient as the number of files grows, and makes it difficult for users to organize data into related groups.
Like many small systems before it, the original Apple Macintosh featured a flat file system, called Macintosh File System. Its version of Mac OS was unusual in that the file management software (Macintosh Finder) created the illusion of a partially hierarchical filing system on top of MFS. This structure meant that every file on a disk had to have a unique name, even if it appeared to be in a separate folder. MFS was quickly replaced with Hierarchical File System, which supported real directories.

[edit] File systems under Unix-like operating systems

Wikibooks Guide to Unix has a page on the topic of
Filesystems and Swap
Unix-like operating systems create a virtual file system, which makes all the files on all the devices appear to exist in a single hierarchy. This means, in those systems, there is one root directory, and every file existing on the system is located under it somewhere. Furthermore, the root directory does not have to be in any physical place. It might not be on your first hard drive - it might not even be on your computer. Unix-like systems can use a network shared resource as its root directory.
Unix-like systems assign a device name to each device, but this is not how the files on that device are accessed. Instead, to gain access to files on another device, you must first inform the operating system where in the directory tree you would like those files to appear. This process is called mounting a file system. For example, to access the files on a CD-ROM, one must tell the operating system "Take the file system from this CD-ROM and make it appear under such-and-such directory". The directory given to the operating system is called the mount point - it might, for example, be /media. The /media directory exists on many Unix systems (as specified in the Filesystem Hierarchy Standard) and is intended specifically for use as a mount point for removable media such as CDs, DVDs and like floppy disks. It may be empty, or it may contain subdirectories for mounting individual devices. Generally, only the administrator (i.e. root user) may authorize the mounting of file systems.
Unix-like operating systems often include software and tools that assist in the mounting process and provide it new functionality. Some of these strategies have been coined "auto-mounting" as a reflection of their purpose.
In many situations, file systems other than the root need to be available as soon as the operating system has booted. All Unix-like systems therefore provide a facility for mounting file systems at boot time. System administrators define these file systems in the configuration file fstab, which also indicates options and mount points.
In some situations, there is no need to mount certain file systems at boot time, although their use may be desired thereafter. There are some utilities for Unix-like systems that allow the mounting of predefined file systems upon demand.
Removable media have become very common with microcomputer platforms. They allow programs and data to be transferred between machines without a physical connection. Common examples include USB flash drives, CD-ROMs and DVDs. Utilities have therefore been developed to detect the presence and availability of a medium and then mount that medium without any user intervention.
Progressive Unix-like systems have also introduced a concept called supermounting; see, for example, the Linux supermount-ng project. For example, a floppy disk that has been supermounted can be physically removed from the system. Under normal circumstances, the disk should have been synchronized and then unmounted before its removal. Provided synchronization has occurred, a different disk can be inserted into the drive. The system automatically notices that the disk has changed and updates the mount point contents to reflect the new medium. Similar functionality is found on standard Windows machines.
A similar innovation preferred by some users is the use of autofs, a system that, like supermounting, eliminates the need for manual mounting commands. The difference from supermount, other than compatibility in an apparent greater range of applications such as access to file systems on network servers, is that devices are mounted transparently when requests to their file systems are made, as would be appropriate for file systems on network servers, rather than relying on events such as the insertion of media, as would be appropriate for removable media.

[edit] File systems under Mac OS X
Mac OS X uses a file system that it inherited from classic Mac OS called HFS Plus. HFS Plus is a metadata-rich and case preserving file system. Due to the Unix roots of Mac OS X, Unix permissions were added to HFS Plus. Later versions of HFS Plus added journaling to prevent corruption of the file system structure and introduced a number of optimizations to the allocation algorithms in an attempt to defragment files automatically without requiring an external defragmenter.
Filenames can be up to 255 characters. HFS Plus uses Unicode to store filenames. On Mac OS X, the filetype can come from the type code, stored in file's metadata, or the filename.
HFS Plus has three kinds of links: Unix-style hard links, Unix-style symbolic links and aliases. Aliases are designed to maintain a link to their original file even if they are moved or renamed; they are not interpreted by the file system itself, but by the File Manager code in userland.
Mac OS X also supports the UFS file system, derived from the BSD Unix Fast File System via NeXTSTEP.

[edit] File systems under Plan 9 from Bell Labs
Plan 9 from Bell Labs was originally designed to extend some of Unix's good points, and to introduce some new ideas of its own while fixing the shortcomings of Unix.
With respect to file systems, the Unix system of treating things as files was continued, but in Plan 9, everything is treated as a file, and accessed as a file would be (i.e., no ioctl or mmap). Perhaps surprisingly, while the file interface is made universal it is also simplified considerably, for example symlinks, hard links and suid are made obsolete, and an atomic create/open operation is introduced. More importantly the set of file operations becomes well defined and subversions of this like ioctl are eliminated.
Secondly, the underlying 9P protocol was used to remove the difference between local and remote files (except for a possible difference in latency). This has the advantage that a device or devices, represented by files, on a remote computer could be used as though it were the local computer's own device(s). This means that under Plan 9, multiple file servers provide access to devices, classing them as file systems. Servers for "synthetic" file systems can also run in user space bringing many of the advantages of micro kernel systems while maintaining the simplicity of the system.
Everything on a Plan 9 system has an abstraction as a file; networking, graphics, debugging, authentication, capabilities, encryption, and other services are accessed via I-O operations on file descriptors. For example, this allows the use of the IP stack of a gateway machine without need of NAT, or provides a network-transparent window system without the need of any extra code.
Another example: a Plan-9 application receives FTP service by opening an FTP site. The ftpfs server handles the open by essentially mounting the remote FTP site as part of the local file system. With ftpfs as an intermediary, the application can now use the usual file-system operations to access the FTP site as if it were part of the local file system. A further example is the mail system which uses file servers that synthesize virtual files and directories to represent a user mailbox as /mail/fs/mbox. The wikifs provides a file system interface to a wiki.
These file systems are organized with the help of private, per-process namespaces, allowing each process to have a different view of the many file systems that provide resources in a distributed system.
The Inferno operating system shares these concepts with Plan 9.

[edit] File systems under Microsoft Windows
Windows makes use of the FAT and NTFS (New Technology File System) file systems.
The FAT (File Allocation Table) filing system, supported by all versions of Microsoft Windows, was an evolution of that used in Microsoft's earlier operating system (MS-DOS which in turn was based on 86-DOS). FAT ultimately traces its roots back to the short-lived M-DOS project and Standalone disk BASIC before it. Over the years various features have been added to it, inspired by similar features found on file systems used by operating systems such as Unix.
Older versions of the FAT file system (FAT12 and FAT16) had file name length limits, a limit on the number of entries in the root directory of the file system and had restrictions on the maximum size of FAT-formatted disks or partitions. Specifically, FAT12 and FAT16 had a limit of 8 characters for the file name, and 3 characters for the extension. This is commonly referred to as the filename limit. VFAT, which was an extension to FAT12 and FAT16 introduced in Windows NT 3.5 and subsequently included in Windows 95, allowed long file names (LFN). FAT32 also addressed many of the limits in FAT12 and FAT16, but remains limited compared to NTFS.
NTFS, introduced with the Windows NT operating system, allowed ACL-based permission control. Hard links, multiple file streams, attribute indexing, quota tracking, compression and mount-points for other file systems (called "junctions") are also supported, though not all these features are well-documented.
Unlike many other operating systems, Windows uses a drive letter abstraction at the user level to distinguish one disk or partition from another. For example, the path C:\WINDOWS represents a directory WINDOWS on the partition represented by the letter C. The C drive is most commonly used for the primary hard disk partition, on which Windows is installed and from which it boots. This "tradition" has become so firmly ingrained that bugs came about in older versions of Windows which made assumptions that the drive that the operating system was installed on was C. The tradition of using "C" for the drive letter can be traced to MS-DOS, where the letters A and B were reserved for up to two floppy disk drives; in a common configuration, A would be the 3½-inch floppy drive, and B the 5¼-inch one. Network drives may also be mapped to drive letters.

MCSE-qs-1

1) You want your computer to be able to dual boot. Your computer is already loaded with Windows 98. Now you want to install Windows 2000 Professional using the same partition on your computer, on which Windows 98 is residing. Which file system you can use? [Select 2].
FAT
FAT32
NTFS
HPFS

Correct Answer: A,B.
Explanation:
You want to install Windows 2000 Professional on the same partition as that of Windows 98. Windows 98 supports FAT (FAT16) and FAT32. It doesn’t support NTFS file system. Therefore, you need to install 2000 Professional either on the FAT file systems or on the FAT32 for dual boot.

History of Operating systems

earliest computers
The first computers were made with intricate gear systems by the Greeks. These computers turned out to be too delicate for the technological capabilities of the time and were abandoned as impractical. The Antikythera mechanism, discovered in a shipwreck in 1900, is an early mechanical analog computer from between 150 BCE and 100 BCE. The Antikythera mechanism used a system of 37 gears to compute the positions of the sun and the moon through the zodiac on the Egyptian calendar, and possibly also the fixed stars and five planets known in antiquity (Mercury, Venus, Mars, Jupiter, and Saturn) for any time in the future or past. The system of gears added and subtracted angular velocities to compute differentials. The Antikythera mechanism could accurately predict eclipses and could draw up accurate astrological charts for important leaders. It is likely that the Antikythera mechanism was based on an astrological computer created by Archimedes of Syracuse in the 3rd century BCE.
The first modern computers were made by the Inca using ropes and pulleys. Knots in the ropes served the purpose of binary digits. The Inca had several of these computers and used them for tax and government records. In addition to keeping track of taxes, the Inca computers held data bases on all of the resources of the Inca empire, allowing for efficient allocation of resources in response to local disasters (storms, drought, earthquakes, etc.). Spanish soldiers acting on orders of Roman Catholic priests destroyed all but one of the Inca computers in the mistaken belief that any device that could give accurate information about distant conditions must be a divination device powered by the Christian “Devil” (and many modern Luddites continue to view computers as Satanically possessed devices).
In the 1800s, the first computers were programmable devices for controlling the weaving machines in the factories of the Industrial Revolution. Created by Charles Babbage, these early computers used Punch cards as data storage (the cards contained the control codes for the various patterns). These cards were very similiar to the famous Hollerinth cards developed later. The first computer programmer was Lady Ada, for whom the Ada programming language is named.
In 1833 Charles babbage proposed a mechanical computer with all of the elements of a modern computer, including control, arithmetic, and memory, but the technology of the day couldn’t produce gears with enough precision or reliability to make his computer possible.
In the 1900s, researchers started experimenting with both analog and digital computers using vacuum tubes. Some of the most successful early computers were analog computers, capable of performing advanced calculus problems rather quickly. But the real future of computing was digital rather than analog. Building on the technology and math used for telephone and telegraph switching networks, researchers started building the first electronic digital computers.
The first modern computer was the German Zuse computer (Z3) in 1941. In 1944 Howard Aiken of Harvard University created the Harvard Mark I and Mark II. The Mark I was primarily mechanical, while the Mark II was primarily based on reed relays. Telephone and telegraph companies had been using reed relays for the logic circuits needed for large scale switching networks.
The first modern electronic computer was the ENIAC in 1946, using 18,000 vacuum tubes. See below for information on Von Neumann’s important contributions.
The first solid-state (or transistor) computer was the TRADIC, built at Bell Laboratories in 1954. The transistor had previously been invented at Bell Labs in 1948.
von Neumann architecture
John Louis von Neumann, mathematician (born János von Neumann 28 December 1903 in Budapest, Hungary, died 8 February 1957 in Washington, D.C.), proposed the stored program concept while professor of mathemtics (one of the orginal six) at Princeton University’s Institute for Advanced Services, in which programs (code) are stored in the same memory as data. The computer knows the difference between code and data by which it is attempting to access at any given moment. When evaluating code, the binary numbers are decoded by some kind of physical logic circuits (later other methods, such as microprogramming, were introduced), and then the instructions are run in hardware. This design is called von Neumann architecture and has been used in almost every digital computer ever made.
Von Neumann architecture introduced flexibility to computers. Previous computers had their programming hard wired into the computer. A particular computer could only do one task (at the time, mostly building artillery tables) and had to be physically rewired to do any new task.
By using numeric codes, von Neumann computers could be reprogrammed for a wide variety of problems, with the decode logic remaining the same.
As processors (especially super computers) get ever faster, the von Neumann bottleneck is starting to become an issue. With data and code both being accessed over the same circuit lines, the processor has to wait for one while the other is being fetched (or written). Well designed data and code caches help, but only when the requested access is already loaded into cache. Some researchers are now experimenting with Harvard architecture to solve the von Neumann bottleneck. In Harvard arrchitecture, named for Howard Aiken’s experimental Harvard Mark I (ASCC) calculator [computer] at Harvard University, a second set of data and address lines along with a second set of memory are set aside for executable code, removing part of the conflict with memory accesses for data.
Von Neumann became an American citizen in 1933 to be eligible to help on top secret work during World War II. There is a story that Oskar Morganstern coached von Neumann and Kurt Gödel on the U.S. Constitution and American history while driving them to their immigration interview. Morganstern asked if they had any questions, and Gödel replied that he had no questions, but had found some logical inconsistencies in the Constitution that he wanted to ask the Immigration officers about. Morganstern recommended that he not ask questions, but just answer them.
Von Neumann occassionally worked with Alan Turing in 1936 through 1938 when Turing was a graduate student at Princeton. Von Neumann was exposed to the concepts of logical design and universal machine proposed in Turing’s 1934 paper “On Computable Numbers with an Application to the Entschiedungs-problem”.
Von Neumann worked with such early computers as the Harvard Mark I, ENIAC, EDVAC, and his own IAS computer.
Early research into computers involved doing the computations to create tables, especially artillery firing tables. Von Neumann was convinced that the future of computers involved applied mathematics to solve specific problems rather than mere table generation. Von Neumann was the first person to use computers for mathematical physics and economics, proving the utility of a general purpose computer.
Von Neumann proposed the concept of stored programs in the 1945 paper “First Draft of a Report on the EDVAC”. Influenced by the idea, Maurice Wilkes of the Cambridge University Mathematical Laboratory designed and built the EDSAC, the world’s first operational, production, stored-program computer.
The first stored computer program ran on the Manchester Mark I [computer] on June 21, 1948.
Von Neumann foresaw the advantages of parallelism in computers, but because of construction limitations of the time, he worked on sequential systems.
Von Neumann advocated the adoption of the bit as the measurement of computer memory and solved many of the problems regarding obtaining reliable answers from unreliable computer components.
Interestingly, von Neumann was opposed to the idea of compilers. When shown the idea for FORTRAN in 1954, von Neumann asked “Why would you want more than machine language?”. Von Neumann had graduate students hand assemble programs into binary code for the IAS machine. Donald Gillies, a student at Princeton, created an assembler to do the work. Von Neumann was angry, claiming “It is a waste of a valuable scientific computing instrument to use it to do clerical work”.
Von Neumann also did important work in set theory (including measure theory), the mathematical foundation for quantum theory (including statistical mechanics), self-adjoint algebras of bounded linear operators on a Hilbert space closed in weak operator topology, non-linear partial differential equations, and automata theory (later applied to cmputers). His work in economics included his 1937 paper “A Model of General Economic Equilibrium” on a multi-sectoral growth model and his 1944 book “Theory of Games and Economic Behavior” (co-authored with Morgenstern) on game theory and uncertainty.
I leave the discussion of von Neumann with a couple of quotations:
“If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is.”
“Anyone who considers arithmetical methods of producing random numbers is, of course, in a state of sin.”
bare hardware
In the earliest days of electronic digital computing, everything was done on the bare hardware. Very few computers existed and those that did exist were experimental in nature. The researchers who were making the first computers were also the programmers and the users. They worked directly on the “bare hardware”. There was no operating system. The experimenters wrote their programs in assembly language and a running program had complete control of the entire computer. Debugging consisted of a combination of fixing both the software and hardware, rewriting the object code and changing the actual computer itself.
The lack of any operating system meant that only one person could use a computer at a time. Even in the research lab, there were many researchers competing for limited computing time. The first solution was a reservation system, with researchers signing up for specific time slots.
The high cost of early computers meant that it was essential that the rare computers be used as efficiently as possible. The reservation system was not particularly efficient. If a researcher finished work early, the computer sat idle until the next time slot. If the researcher's time ran out, the researcher might have to pack up his or her work in an incomplete state at an awkward moment to make room for the next researcher. Even when things were going well, a lot of the time the computer actually sat idle while the researcher studied the results (or studied memory of a crashed program to figure out what went wrong).
computer operators
The solution to this problem was to have programmers prepare their work off-line on some input medium (often on punched cards, paper tape, or magnetic tape) and then hand the work to a computer operator. The computer operator would load up jobs in the order received (with priority overrides based on politics and other factors). Each job still ran one at a time with complete control of the computer, but as soon as a job finished, the operator would transfer the results to some output medium (punched tape, paper tape, magnetic tape, or printed paper) and deliver the results to the appropriate programmer. If the program ran to completion, the result would be some end data. If the program crashed, memory would be transferred to some output medium for the programmer to study (because some of the early business computing systems used magnetic core memory, these became known as “core dumps”)
device drivers and library functions
Soon after the first successes with digital computer experiments, computers moved out of the lab and into practical use. The first practical application of these experimental digital computers was the generation of artillery tables for the British and American armies. Much of the early research in computers was paid for by the British and American militaries. Business and scientific applications followed.
As computer use increased, programmers noticed that they were duplicating the same efforts.
Every programmer was writing his or her own routines for I/O, such as reading input from a magnetic tape or writing output to a line printer. It made sense to write a common device driver for each input or putput device and then have every programmer share the same device drivers rather than each programmer writing his or her own. Some programmers resisted the use of common device drivers in the belief that they could write “more efficient” or faster or "“better” device drivers of their own.
Additionally each programmer was writing his or her own routines for fairly common and repeated functionality, such as mathematics or string functions. Again, it made sense to share the work instead of everyone repeatedly “reinventing the wheel”. These shared functions would be organized into libraries and could be inserted into programs as needed. In the spirit of cooperation among early researchers, these library functions were published and distributed for free, an early example of the power of the open source approach to software development.
1950s
Some operating systems from the 1950s include: FORTRAN Monitor System, General Motors Operating System, Input Output System, SAGE, and SOS.
SAGE (Semi-Automatic Ground Environment), designed to monitor weapons systems, was the first real time control system.
batch systems
Batch systems automated the early approach of having human operators load one program at a time. Instead of having a human operator load each program, software handled the scheduling of jobs. In addition to programmers submitting their jobs,, end users could submit requests to run specific programs with specific data sets (usually stored in files or on cards). The operating system would schedule “batches” of related jobs. Output (punched cards, magnetic tapes, printed material, etc.) would be returned to each user.
Examples of operating systems that were primarily batch-oriented include: BKY, BOS/360, BPS/360, CAL, and Chios.
early 1960s
Some operating systems from the early 1960s include: Admiral, B1, B2, B3, B4, Basic Executive System, BOS/360, EXEC I, EXEC II, Honeywell Executive System, IBM 1410/1710 OS, IBSYS, Input Output Control System, Master Control Program, and SABRE.
The first major transaction processing system was SABRE (Semi-Automatic Business Related Environment), developed by IBM and American Airlines.w78
system calls
The first operating system to introduce system calls was University of Machester’s Atlas I Supervisor.w78
mid 1960s
Some operating systems from the mid-1960s include: Atlas I Supervisor, DOS/360, Input Output Selector, and Master Control Program.
late 1960s
Some operating systems from the late-1960s include: BPS/360, CAL, CHIPPEWA, EXEC 3, and EXEC 4, EXEC 8, GECOS III, George 1, George 2, George 3, George 4, IDASYS, MASTER, Master Control Program, OS/MFT, OS/MFT-II, OS/MVT, OS/PCP, and RCA DOS.
microprocessors
In 1968 a group of scientists and engineers from Mitre Corporation (Bedford, Massachusetts) created Viatron Computer company and an intelligent data terminal using an 8-bit LSI microprocessor from PMOS technology. A year later in 1969 Viatron created the 2140, the first 4-bit LSI microprocessor. At the time MOS was used only for a small number of calculators and there simply wasn’t enough worldwide manufacturing capacity to build these computers in quantity.
Other companies saw the benefit of MOS, starting with Intel’s 1971 release of the 4-bit 4004 as the first commercially available microprocessor. In 1972 Rockwell released the PPS-4 microprocessor, Fairchild released the PPS-25 microprocessor, and Intel released the 8-bit 8008 microprocessor. In 1973 National released the IMP microprocessor.
In 1973 Intel released the faster NMOS 8080 8-bit microprocessor, the first in a long series of microprocessors that led to the current Pentium.
In 1974 Motorola released the 6800, which included two accumulators, index registers, and memory-mapped I/O. Monolithic Memories introduced bit-slice microprocessing. In 1975 Texas Instruments introduced a 4-bit slice microprocessor and Fairchild introduced the F-8 microprocessor.
early 1970s
Some operating systems from the early-1970s include: BKY, Chios, DOS/VS, Master Control Program, OS/VS1, and UNIX.
In 1970 Ken Thompson of AT&T Bell Labs suggested the name “Unix” for the operating system that had been under development since 1969. The name was an intentional pun on AT&T’s earlier Multics project (uni- means “one”, multi- means “many”).
mid 1970s
Some operating systems from the mid-1970s include: Master Control Program.
In 1973 the kernel of Unix was rewritten in the C programming language. This made Unix the world’s first portable operating system, capable of being easily ported (moved) to any hardware. This was a major advantage for Unix and led to its widespread use in the multi-platform environments of colleges and universities.
late 1970s
Some operating systems from the late-1970s include: EMAS 2900, General Comprehensive OS, OpenVMS, OS/MVS.
1980s
Some operating systems from the 1980s include: AmigaOS, DOS/VSE, HP-UX, Macintosh, MS-DOS, and ULTRIX.
1990s
Some operating systems from the 1990s include: BeOS, BSDi, FreeBSD, NeXT, OS/2, Windows 95, Windows 98, and Windows NT.
2000s
Some operating systems from the 2000s include: Mac OS X, Syllable, Windows 2000, Windows Server 2003, Windows ME, and Windows XP.
UNIX takes over mainframes
I am skipping ahead to the development and spread of UNIX†, not because the early history isn’t interesting, but because I notice that a lot of people are searching for information on UNIX history.
UNIX was orginally developed in a laboratory at AT&T’s Bell Labs (now an independent corporation known as Lucent Technologies). At the time, AT&T was prohibited from selling computers or software, but was allowed to develop its own software and computers for internal use. A few newly hired engineers were unable to get valuable mainframe computer time because of lack of seniority and resorted to writing their own operating system (UNIX) and programming language (C) to run on an unused mainframe computer still in the original box (the manufacturer had gone out of business before shipping an operating system).
AT&T’s consent decree with the U.S. Justice Department on monopoly charges was interpretted as allowing AT&T to release UNIX as an open source operating system for academic use. Ken Thompson, one of the originators of UNIX, took UNIX to the University of California, Berkeley, where students quickly started making improvements and modifications, leading to the world famous Berkeley Standard Distribution (BSD) form of UNIX.
UNIX quickly spread throughout the academic world, as it solved the problem of keeping track of many (sometimes dozens) of proprietary operating systems on university computers. With UNIX all of the computers from many different manufacturers could run the same operating system and share the same programs (recompiled on each processor).
When AT&T settled yet another monopoly case, the company was broken up into “Baby Bells” (the regional companies operating local phone service) and the central company (which had the long distance business and Bell Labs). AT&T (as well as the Baby Bells) was allowed to enter the computer business. AT&T gave academia a specific deadline to stop using “encumbered code” (that is, any of AT&T’s source code anywhere in their versions of UNIX).
This led to the development of free open source projects such as FreeBSD, NetBSD, and OpenBSD, as well as commercial operating systems based on the BSD code.
Meanwhile, AT&T developed its own version of UNIX, called System V. Although AT&T eventually sold off UNIX, this also spawned a group of commercial operating systems known as Sys V UNIXes.
UNIX quickly swept through the commercial world, pushing aside almost all proprietary mainframe operating systems. Only IBM’s MVS and DEC’s OpenVMS survived the UNIX onslaught.
“Vendors such as Sun, IBM, DEC, SCO, and HP modified Unix to differentiate their products. This splintered Unix to a degree, though not quite as much as is usually perceived. Necessity being the mother of invention, programmers have created development tools that help them work around the differences between Unix flavors. As a result, there is a large body of software based on source code that will automatically configure itself to compile on most Unix platforms, including Intel-based Unix.
Regardless, Microsoft would leverage the perception that Unix is splintered beyond hope, and present Windows NT as a more consistent multi-platform alternative.” —Nicholas Petreley, “The new Unix alters NT’s orbit”, NC Worldw74
UNIX to the desktop
Among the early commercial attempts to deploy UNIX† on desktop computers was AT&T selling UNIX in an Olivetti box running a %20680x0%20assembly%20language%20is%20discussed%20in%20the%20

What is operating system?

operating system (OS) is the software that manages the sharing of the resources of a computer and provides programmers with an interface used to access those resources. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the system. At the foundation of all system software, an operating system performs basic tasks such as controlling and allocating memory, prioritizing system requests, controlling input and output devices, facilitating networking and managing file systems. Most operating systems come with an application that provides a user interface for managing the operating system, such as a command line interpreter or graphical user interface. The operating system forms a platform for other system software and for application software.
The most commonly-used contemporary desktop and laptop (notebook) OS is Microsoft Windows. More powerful servers often employ Linux, FreeBSD, and other Unix-like systems. However, these Unix-like operating systems, especially Mac OS X, are also used on personal computers.
Contents[hide]
1 Services
1.1 Process management
1.2 Memory management
1.3 Disk and file systems
1.4 Networking
1.5 Security
1.5.1 Internal security
1.5.2 External security
1.6 Graphical user interfaces
1.7 Device drivers
2 History
2.1 Mainframes
2.2 Microcomputers
3 Some Operating Systems
3.1 Microsoft Windows
3.2 Plan 9
3.3 Unix and Unix-like operating systems
3.3.1 Mac OS X
3.4 Embedded systems
3.5 Hobby operating system development
3.6 Other
4 References
5 See also
6 External links
//

[edit] Services
Main article: Kernel (computer science)
Structure of the Operating System
Layer 5: The System operator process
Layer 4: User Programs
Layer 3: I/O Management
Layer 2: Operator-process communication
Layer 1: Memory and drum management
Layer 0: Processor allocation and multiprogram

[edit] Process management
Every program running on a computer, be it a service or an application, is a process. As long as a von Neumann architecture is used to build computers, only one process per CPU can be run at a time.[citation needed] Older microcomputer OSes such as MS-DOS did not attempt to bypass this limit, with the exception of interrupt processing, and only one process could be run under them (although DOS itself featured TSR as a very partial and not too easy to use solution).
Most operating systems enable concurrent execution of many processes and programs at once via multitasking, even with one CPU. The mechanism was used in mainframes since the early 1960s, but in the personal computers it became available in 1990s. Process management is an operating system's way of dealing with running those multiple processes. On the most fundamental of computers (those containing one processor with one core) multitasking is done by simply switching processes quickly. Depending on the operating system, as more processes run, either each time slice will become smaller or there will be a longer delay before each process is given a chance to run. Process management involves computing and distributing CPU time as well as other resources. Most operating systems allow a process to be assigned a priority which affects its allocation of CPU time. Interactive operating systems also employ some level of feedback in which the task with which the user is working receives higher priority. Interrupt driven processes will normally run at a very high priority. In many systems there is a background process, such as the System Idle Process in Windows, which will run when no other process is waiting for the CPU.

[edit] Memory management
Current computer architectures arrange the computer's system in a hierarchical manner, starting from the fastest registers, CPU cache, random access memory and disk storage. An operating system's disk manager coordinates the use of these various types of memory by tracking which one is available, which is to be allocated or deallocated and how to move data between them. This activity, usually referred to as virtual memory management, increases the amount of memory available for each process by making the disk storage seem like main memory. There is a speed penalty associated with using disks or other slower storage as memory – if running processes require significantly more RAM than is available, the system may start thrashing. This can happen either because one process requires a large amount of RAM or because two or more processes compete for a larger amount of memory than is available. This then leads to constant transfer of each process's data to slower storage.
Another important part of memory management is managing virtual addresses. If multiple processes are in memory at once, they must be prevented from interfering with each other's memory (unless there is an explicit request to utilise shared memory). This is achieved by having separate address spaces. Each process sees the whole virtual address space, typically from address 0 up to the maximum size of virtual memory, as uniquely assigned to it. The operating system maintains a page table that match virtual addresses to physical addresses. These memory allocations are tracked so that when a process terminates, all memory used by that process can be made available for other processes.
The operating system can also write inactive memory pages to secondary storage. This process is called "paging" or "swapping" – the terminology varies between operating systems.
It is also typical for operating systems to employ otherwise unused physical memory as a page cache; requests for data from a slower device can be retained in memory to improve performance. The operating system can also pre-load the in-memory cache with data that may be requested by the user in the near future; SuperFetch is an example of this.

[edit] Disk and file systems
Generally, operating systems include support for file systems.
Modern file systems comprise a hierarchy of directories. While the idea is conceptually similar across all general-purpose file systems, some differences in implementation exist. Two noticeable examples of this are the character used to separate directories, and case sensitivity.
Unix demarcates its path components with a slash (/), a convention followed by operating systems that emulated it or at least its concept of hierarchical directories, such as Linux, Amiga OS and Mac OS X. MS-DOS also emulated this feature, but had already also adopted the CP/M convention of using slashes for additional options to commands, so instead used the backslash (\) as its component separator. Microsoft Windows continues with this convention; Japanese editions of Windows use ¥, and Korean editions use ₩.[1] Prior to Mac OS X, versions of Mac OS use a colon (:) for a path separator. RISC OS uses a period (.).
Unix and Unix-like operating systems allow for any character in file names other than the slash and NUL characters (including line feed (LF) and other control characters). Unix file names are case sensitive, which allows multiple files to be created with names that differ only in case. By contrast, Microsoft Windows file names are not case sensitive by default. Windows also has a larger set of punctuation characters that are not allowed in file names.
File systems may provide journaling, which provides safe recovery in the event of a system crash. A journaled file system writes information twice: first to the journal, which is a log of file system operations, then to its proper place in the ordinary file system. In the event of a crash, the system can recover to a consistent state by replaying a portion of the journal. In contrast, non-journaled file systems typically need to be examined in their entirety by a utility such as fsck or chkdsk. Soft updates is an alternative to journalling that avoids the redundant writes by carefully ordering the update operations. Log-structured file systems and ZFS also differ from traditional journaled file systems in that they avoid inconsistencies by always writing new copies of the data, eschewing in-place updates.
Many Linux distributions support some or all of ext2, ext3, ReiserFS, Reiser4, GFS, GFS2, OCFS, OCFS2, and NILFS. Linux also has full support for XFS and JFS, along with the FAT file systems, and NTFS.
Microsoft Windows includes support for FAT12, FAT16, FAT32, and NTFS. The NTFS file system is the most efficient and reliable of the four Windows file systems, and as of Windows Vista, is the only file system which the operating system can be installed on. Windows Embedded CE 6.0 introduced ExFAT, a file system suitable for flash drives.
Mac OS X supports HFS+ with journaling as its primary file system. It is derived from the Hierarchical File System of the earlier Mac OS. Mac OS X has facilities to read and write FAT16, FAT32, NTFS and other file systems, but cannot be installed to them.
Common to all these (and other) operating systems is support for file systems typically found on removable media. FAT12 is the file system most commonly found on floppy discs. ISO 9660 and Universal Disk Format are two common formats that target Compact Discs and DVDs, respectively. Mount Rainier is a newer extension to UDF supported by Linux 2.6 kernels and Windows Vista that facilitates rewriting to DVDs in the same fashion as has been possible with floppy disks.

[edit] Networking
Most current operating systems are capable of using the TCP/IP networking protocols. This means that computers running dissimilar operating systems can participate in a common network for sharing resources such as computing, files, printers, and scanners using either wired or wireless connections.
Many operating systems also support one or more vendor-specific legacy networking protocols as well, for example, SNA on IBM systems, DECnet on systems from Digital Equipment Corporation, and Microsoft-specific protocols on Windows. Specific protocols for specific tasks may also be supported such as NFS for file access.

[edit] Security
Many operating systems include some level of security. Security is based on the two ideas that:
The operating system provides access to a number of resources, directly or indirectly, such as files on a local disk, privileged system calls, personal information about users, and the services offered by the programs running on the system;
The operating system is capable of distinguishing between some requesters of these resources who are authorized (allowed) to access the resource, and others who are not authorized (forbidden). While some systems may simply distinguish between "privileged" and "non-privileged", systems commonly have a form of requester identity, such as a user name. Requesters, in turn, divide into two categories:
Internal security: an already running program. On some systems, a program once it is running has no limitations, but commonly the program has an identity which it keeps and is used to check all of its requests for resources.
External security: a new request from outside the computer, such as a login at a connected console or some kind of network connection. To establish identity there may be a process of authentication. Often a username must be quoted, and each username may have a password. Other methods of authentication, such as magnetic cards or biometric data, might be used instead. In some cases, especially connections from the network, resources may be accessed with no authentication at all.
In addition to the allow/disallow model of security, a system with a high level of security will also offer auditing options. These would allow tracking of requests for access to resources (such as, "who has been reading this file?").
Security of operating systems has long been a concern because of highly sensitive data held on computers, both of a commercial and military nature. The United States Government Department of Defense (DoD) created the Trusted Computer System Evaluation Criteria (TCSEC) which is a standard that sets basic requirements for assessing the effectiveness of security. This became of vital importance to operating system makers, because the TCSEC was used to evaluate, classify and select computer systems being considered for the processing, storage and retrieval of sensitive or classified information.

[edit] Internal security
Internal security can be thought of as protecting the computer's resources from the programs concurrently running on the system. Most operating systems set programs running natively on the computer's processor, so the problem arises of how to stop these programs doing the same task and having the same privileges as the operating system (which is after all just a program too). Processors used for general purpose operating systems generally have a hardware concept of privilege. Generally less privileged programs are automatically blocked from using certain hardware instructions, such as those to read or write from external devices like disks. Instead, they have to ask the privileged program (operating system kernel) to read or write. The operating system therefore gets the chance to check the program's identity and allow or refuse the request.
An alternative strategy, and the only sandbox strategy available in systems that do not meet the Popek and Goldberg virtualization requirements, is the operating system not running user programs as native code, but instead either emulates a processor or provides a host for a p-code based system such as Java.
Internal security is especially relevant for multi-user systems; it allows each user of the system to have private files that the other users cannot tamper with or read. Internal security is also vital if auditing is to be of any use, since a program can potentially bypass the operating system, inclusive of bypassing auditing.

[edit] External security
Typically an operating system offers (or hosts) various services to other network computers and users. These services are usually provided through ports or numbered access points beyond the operating system's network address. Services include offerings such as file sharing, print services, email, web sites, and file transfer protocols (FTP), most of which can have compromised security.
At the front line of security are hardware devices known as firewalls or intrusion detection/prevention systems. At the operating system level, there are a number of software firewalls available, as well as intrusion detection/prevention systems. Most modern operating systems include a software firewall, which is enabled by default. A software firewall can be configured to allow or deny network traffic to or from a service or application running on the operating system. Therefore, one can install and be running an insecure service, such as Telnet or FTP, and not have to be threatened by a security breach because the firewall would deny all traffic trying to connect to the service on that port.

[edit] Graphical user interfaces
Today, most modern operating systems contain Graphical User Interfaces. A few older operating systems tightly integrated the GUI into the kernel—for example, in the original implementations of Microsoft Windows and Mac OS, the graphical subsystem was actually part of the kernel. More modern operating systems are modular, separating the graphics subsystem from the kernel and the Operating System (as has done in Linux, and now on Mac OS X).
Many operating systems allow the user to install or create any user interface they desire. The X Window System in conjunction with GNOME or KDE is a commonly found setup on most Unix and Unix-like (BSD, Linux, Minix) systems.
Graphical user interfaces evolve over time. For example, Windows has modified its user interface almost every time a new major version of Windows is released, and the Mac OS GUI changed dramatically with the introduction of Mac OS X in 2001.

[edit] Device drivers
A device driver is a specific type of computer software developed to allow interaction with hardware devices. Typically this constitutes an interface for communicating with the device, through the specific computer bus or communications subsystem that the hardware is connected to, providing commands to and/or receiving data from the device, and on the other end, the requisite interfaces to the operating system and software applications. It is a specialized hardware-dependent computer program which is also operating system specific that enables another program, typically an operating system or applications software package or computer program running under the operating system kernel, to interact transparently with a hardware device, and usually provides the requisite interrupt handling necessary for any necessary asynchronous time-dependent hardware interfacing needs.
The key design goal of device drivers is abstraction. Every model of hardware (even within the same class of device) is different. Newer models also are released by manufacturers that provide more reliable or better performance and these newer models are often controlled differently. Computers and their operating systems cannot be expected to know how to control every device, both now and in the future. To solve this problem, OSes essentially dictate how every type of device should be controlled. The function of the device driver is then to translate these OS mandated function calls into device specific calls. In theory a new device, which is controlled in a new manner, should function correctly if a suitable driver is available. This new driver will ensure that the device appears to operate as usual from the operating systems' point of view for any person..

[edit] History
Main article: History of operating systems
The first computers did not have operating systems. By the early 1960s, commercial computer vendors were supplying quite extensive tools for streamlining the development, scheduling, and execution of jobs on batch processing systems. Examples were produced by UNIVAC and Control Data Corporation, amongst others.

[edit] Mainframes
Through the 1960s, many major features were pioneered in the field of operating systems. The development of the IBM System/360 produced a family of mainframe computers available in widely differing capacities and price points, for which a single operating system OS/360 was planned (rather than developing ad-hoc programs for every individual model). This concept of a single OS spanning an entire product line was crucial for the success of System/360 and, in fact, IBM's current mainframe operating systems are distant descendants of this original system; applications written for the OS/360 can still be run on modern machines. OS/360 also contained another important advance: the development of the hard disk permanent storage device (which IBM called DASD).
Control Data Corporation developed the SCOPE operating system in the 1960s, for batch processing. In cooperation with the University of Minnesota, the KRONOS and later the NOS operating systems were developed during the 1970s, which supported simultaneous batch and timesharing use. Like many commercial timesharing systems, its interface was an extension of the Dartmouth BASIC operating systems, one of the pioneering efforts in timesharing and programming languages. In the late 1970s, Control Data and the University of Illinois developed the PLATO operating system, which used plasma panel displays and long-distance time sharing networks. Plato was remarkably innovative for its time, featuring real-time chat, and multi-user graphical games.
Burroughs Corporation introduced the B5000 in 1961 with the MCP, (Master Control Program) operating system. The B5000 was a stack machine designed to exclusively support high-level languages with no machine language or assembler and indeed the MCP was the first OS to be written exclusively in a high-level language (ESPOL, a dialect of ALGOL). MCP also introduced many other ground-breaking innovations, such as being the first commercial implementation of virtual memory. MCP is still in use today in the Unisys ClearPath/MCP line of computers.
UNIVAC, the first commercial computer manufacturer, produced a series of EXEC operating systems. Like all early main-frame systems, this was a batch-oriented system that managed magnetic drums, disks, card readers and line printers. In the 1970s, UNIVAC produced the Real-Time Basic (RTB) system to support large-scale time sharing, also patterned after the Dartmouth BASIC system.
General Electric and MIT developed General Electric Comprehensive Operating Supervisor (GECOS), which introduced the concept of ringed security privilege levels. After acquisition by Honeywell it was renamed to General Comprehensive Operating System (GCOS).
Digital Equipment Corporation developed many operating systems for its various computer lines, including TOPS-10 and TOPS-20 time sharing systems for the 36-bit PDP-10 class systems. Prior to the widespread use of UNIX, TOPS-10 was a particularly popular system in universities, and in the early ARPANET community.
In the late 1960s through the late 1970s, several hardware capabilities evolved that allowed similar or ported software to run on more than one system. Early systems had utilized microprogramming to implement features on their systems in order to permit different underlying architecture to appear to be the same as others in a series. In fact most 360's after the 360/40 (except the 360/165 and 360/168) were microprogrammed implementations. But soon other means of achieving application compatibility were proven to be more significant.
The enormous investment in software for these systems made since 1960s caused most of the original computer manufacturers to continue to develop compatible operating systems along with the hardware. The notable supported mainframe operating systems include:
Burroughs MCP -- B5000,1961 to Unisys Clearpath/MCP, present.
IBM OS/360 -- IBM System/360, 1964 to IBM z/OS, present.
IBM CP-67 -- IBM System/360, 1967 to IBM z/VM, present.
UNIVAC EXEC 8 -- UNIVAC 1108, 1964, to Unisys Clearpath IX, present.

[edit] Microcomputers
The first microcomputers did not have the capacity or need for the elaborate operating systems that had been developed for mainframes and minis; minimalistic operating systems were developed, often loaded from ROM and known as Monitors. One notable early disk-based operating system was CP/M, which was supported on many early microcomputers and was closely imitated in MS-DOS, which became wildly popular as the operating system chosen for the IBM PC (IBM's version of it was called IBM-DOS or PC-DOS), its successors making Microsoft one of the world's most profitable companies. In the 80's Apple Computer Inc. (now Apple Inc.) abandoned its popular Apple II series of microcomputers to introduce the Apple Macintosh computer with the an innovative Graphical User Interface (GUI) to the Mac OS.
The introduction of the Intel 80386 CPU chip with 32-bit architecture and paging capabilities, provided personal computers with the ability to run multitasking operating systems like those of earlier minicomputers and mainframes. Microsoft's responded to this progress by hiring Dave Cutler, who had developed the VMS operating system for Digital Equipment Corporation. He would lead the development of the Windows NT operating system, which continues to serve as the basis for Microsoft's operating systems line. Steve Jobs, a co-founder of Apple Inc., started NeXT Computer Inc., which developed the Unix-like NEXTSTEP operating system. NEXTSTEP would later be acquired by Apple Inc. and used, along with code from FreeBSD as the core of Mac OS X.
Minix, an academic teaching tool which could be run on early PCs, would inspire another reimplementation of Unix, called Linux. Started by computer student Linus Torvalds with cooperation from volunteers over the internet, developed a kernel which was combined with the tools from the GNU Project. The Berkeley Software Distribution, known as BSD, is the UNIX derivative distributed by the University of California, Berkeley, starting in the 1970s. Freely distributed and ported to many minicomputers, it eventually also gained a following for use on PCs, mainly as FreeBSD, NetBSD and OpenBSD.

[edit] Some Operating Systems

[edit] Microsoft Windows
The Microsoft Windows family of operating systems originated as an add-on to the older MS-DOS operating system for the IBM PC. Modern versions are based on the newer Windows NT kernel that was originally intended for OS/2 and borrowed from VMS. Windows runs on x86, x86-64 and Itanium processors. Earlier versions also ran on the DEC Alpha, MIPS, Fairchild (later Intergraph) Clipper and PowerPC architectures (some work was done to port it to the SPARC architecture).
As of September 2007, Microsoft Windows holds a large amount of the worldwide desktop market share. Windows is also used on servers, supporting applications such as web servers and database servers. In recent years, Microsoft has spent significant marketing and research & development money to demonstrate that Windows is capable of running any enterprise application, which has resulted in consistent price/performance records (see the TPC) and significant acceptance in the enterprise market.
The most widely used version of the Microsoft Windows family is Windows XP, released on October 25, 2001.
In November 2006, after more than five years of development work, Microsoft released Windows Vista, a major new operating system version of Microsoft Windows family which contains a large number of new features and architectural changes. Chief amongst these are a new user interface and visual style called Windows Aero, a number of new security features such as User Account Control, and few new multimedia applications such as Windows DVD Maker.
Microsoft has announced a new version codenamed Windows 7 will be released in 2009 or later.

[edit] Plan 9
Ken Thompson, Dennis Ritchie and Douglas McIlroy at Bell Labs designed and developed the C programming language to build the operating system Unix. Programmers at Bell Labs went on to develop Plan 9 and Inferno, which were engineered for modern distributed environments. Plan 9 was designed from the start to be a networked operating system, and had graphics built-in, unlike Unix, which added these features to the design later. Plan 9 has yet to become as popular as Unix derivatives, but it has an expanding community of developers. It is currently released under the Lucent Public License. Inferno was sold to Vita Nuova Holdings and has been released under a GPL/MIT license.

[edit] Unix and Unix-like operating systems

A customized KDE desktop running under Linux.
Ken Thompson wrote B, mainly based on BCPL, which he used to write Unix, based on his experience in the MULTICS project. B became C, and Unix developed into a large, complex family of inter-related OS and Development Environments which have been influential in every modern OS (see History).
The Unix-like family is a diverse group of operating systems, with several major sub-categories including System V, BSD, and Linux. The name "UNIX" is a trademark of The Open Group which licenses it for use with any operating system that has been shown to conform to their definitions. "Unix-like" is commonly used to refer to the large set of operating systems which resemble the original Unix.
Unix systems run on a wide variety of machine architectures. They are used heavily as server systems in business, as well as workstations in academic and engineering environments. Free software Unix variants, such as GNU, Linux and BSD, are popular in these areas. The market share for Linux is divided between many different distributions. Enterprise class distributions by Red Hat or SuSe are used by corporations, but some home users may use those products. Historically home users typically installed a distribution themselves, but in 2007 Dell began to offer the Ubuntu Linux distribution on home PCs. Linux on the desktop is also popular in the developer and hobbyist operating system development communities. (see below)
Market share statistics for freely available operating systems are usually inaccurate since most free operating systems are not purchased, making usage under-represented. On the other hand, market share statistics based on total downloads of free operating systems are often inflated, as there is no economic disincentive to acquire multiple operating systems so users can download multiple systems, test them, and decide which they like best.
Some Unix variants like HP's HP-UX and IBM's AIX are designed to run only on that vendor's hardware. Others, such as Solaris, can run on multiple types of hardware, including x86 servers and PCs. Apple's Mac OS X, a hybrid kernel-based BSD variant derived from NeXTSTEP, Mach, and FreeBSD, has replaced Apple's earlier (non-Unix) Mac OS.
Unix interoperability was sought by establishing the POSIX standard. The POSIX standard can be applied to any operating system, although it was originally created for various Unix variants.

[edit] Mac OS X
Mac OS X is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Inc., the latest of which is pre-loaded on all currently shipping Macintosh computers. Mac OS X is the successor to the original Mac OS, which had been Apple's primary operating system since 1984. Unlike its predecessor, Mac OS X is a UNIX operating system built on technology that had been developed at NeXT through the second half of the 1980s and up until Apple purchased the company in early 1997.
The operating system was first released in 1999 as Mac OS X Server 1.0, with a desktop-oriented version (Mac OS X v10.0) following in March 2001. Since then, five more distinct "end-user" and "server" editions of Mac OS X have been released, the most recent being Mac OS X v10.5, which was first made available in October 2007. Releases of Mac OS X are named after big cats; Mac OS X v10.5 is usually referred to by Apple and users as "Leopard".
The server edition, Mac OS X Server, is architecturally identical to its desktop counterpart but usually runs on Apple's line of Macintosh server hardware. Mac OS X Server includes workgroup management and administration software tools that provide simplified access to key network services, including a mail transfer agent, a Samba server, an LDAP server, a domain name server, and others.

[edit] Embedded systems
Embedded systems use a variety of dedicated operating systems. In some cases, the "operating system" software is directly linked to the application to produce a monolithic special-purpose program. In the simplest embedded systems, there is no distinction between the OS and the application. Embedded systems that have certain time requirements are known as real-time operating systems.
Operating systems such as VxWorks, eCos, and Palm OS, are unrelated to Unix and Windows. Windows CE is descendant of Windows, and several embedded BSD and Linux distributions exist.

[edit] Hobby operating system development
Operating system development, or OSDev for short, as a hobby has a large cult following. As such, operating systems, such as Linux, have derived from hobby operating system projects. The design and implementation of an operating system requires skill and determination, and the term can cover anything from a basic "Hello World" boot loader[citation needed] to a fully featured kernel. One classical example of this is the Minix Operating System -- an OS that was designed as a teaching tool but was heavily used by hobbyists before Linux eclipsed it in popularity.

[edit] Other
Older operating systems which are still used in niche markets include OS/2 from IBM; Mac OS, the non-Unix precursor to Apple's Mac OS X; BeOS; XTS-300. Some, most notably AmigaOS and RISC OS, continue to be developed as minority platforms for enthusiast communities and specialist applications. OpenVMS formerly from DEC, is still under active development by Hewlett-Packard.
Research and development of new operating systems continues. GNU Hurd is designed to be backwards compatible with Unix, but with enhanced functionality and a microkernel architecture. Singularity is a project at Microsoft Research to develop an operating system with better memory protection based on the .Net managed code model.

Microsoft Vista

Answers for the previous questions

1) E 2) C 3) A 4) A 5) D

MCSE

What is MCSE?

A Microsoft Certified Systems Engineer (MCSE) is a person who is certified by Microsoft to work with networking concepts and operation systems. Several years ago, Microsoft opened up learning and training centers all over the country to teach people how to become MCSE qualified within the Microsoft platforms, and interest has been booming ever since.
A person who is interested in becoming an MCSE has to pass a credit-by-exam test. This allows a person to work within the latest system. With each new system that comes out, however, there are other certified exams that an MCSE must take and pass in order to maintain certification. For instance, if an MCSE is certified for the year 2002 and 2000, he or she must take at least two certification exams – one for each year of certification.
This upgrading of certification continues as long as the person wishes to continue to be an MCSE. The reason for the testing, and for proving proficiency for each year, is that Microsoft is changing constantly, and the information for earlier operating and networking systems changes with each new application.
To become certified by Microsoft, one must take the Microsoft Certification Exam at a designated Testing Center. Microsoft offers courses to help students pass the MCSE exams. There is, however, limited seating for the courses. At the same time, the training centers run courses constantly in order to serve as many of those who want to become an MCSE as possible.
It takes time and commitment to get through the courses necessary to become an MCSE. Depending on how much time a student devotes to the process, however, it can take as little as a year. On the other hand, the courses can take as long as two years. A student who already has an Associate in Science degree and has applied computer knowledge can often make it through the program even faster.
There is a very high demand for MCSE qualified individuals. Employers see the certification as a plus when hiring a new employee, especially in the field of computers or communications. Although potential employers also consider experience, the certification shows that the potential employee has a defined knowledge of how Microsoft systems work.

Proceed(next 3 questions)

3)When using WINNT32, the file WINNT32.LOG is the default file name for the parameter.
A)DEBUG
B)LOG
C)RECORD
D)RESPONSE
E)None of the above
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4)Windows 2000 supports Kerebos authentication.
A)TRUE
B)FALSE

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5)What is the minimum recommended processor for a Windows 2000 Server installation?
A)133MHz
B)166MHz
C)250MHz
D)300MHz
E)366MHz

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Next

IF you can answer these questions you can go to next three questions in the next Post

" proceed"

MCSE( general)

1.Which of the following operating systems can be upgraded to Windows 2000?

A)Windows 95
B) Windows 98
C) Windows 98SE
D) Windows NT 3.5.1
E) All of the above

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2.What should be download and run to check a system for Windows 2000 compatibilty?

A)Windows 2000 System Analysis Tool (SAT)
B)windows 2000 Installation Preview
C)Windows 2000 Readiness Analyzer
D)Windows 2000 System Integrity Checker
E)None of the above
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