Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Dos shopping experience:

1. Compare - without doubt the biggest advantage that the Dos offers shoppers today is the ability to compare thousands of Dos at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Dos? Wrong! If the Dos is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Dos then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Dos? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Dos and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Dos wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Dos then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Dos site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Dos, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Dos, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

command.DOS (from Disk Operating System) commonly refers to the family of closely related operating systems which dominated the IBM PC compatible market between 1981 and 1995 (or until about 2000, if Windows 9x systems are included): DR-DOS, FreeDOS, MS-DOS, Novell-DOS, OpenDOS, PC-DOS, PTS-DOS, ROM-DOS and several others. They are single user, single task systems. MS-DOS from Microsoft was the most widely used. These operating systems ran on IBM PC type hardware using the Intel x86 CPUs or their compatible cousins from other makers. MS-DOS, inspired by CP/M, is still common today and was the foundation for many of Microsoft's operating systems (from Windows 1.0 through Windows Me). MS-DOS was later used as the foundation for their operating systems.

History MS-DOS (and the IBM PC-DOS which was licensed therefrom), and its predecessor, 86-DOS, was inspired by CP/M (Control Program /(for) Microcomputers) — which was the dominant disk operating system for 8-bit Intel 8080 and Zilog Zilog Z-80 based microcomputers. Tim Paterson at Seattle Computer Products developed a variant of CP/M-80, intended as an internal product for testing the SCP's new 8086 Central processing unit card for the S-100 bus. It did not run on the 8080 CPU needed for CP/M-80. The system was named 86-DOS (it had initially been called QDOS, which stood for Quick and Dirty Operating System).

A full time operating system was needed for IBM's 8086 line of computers, but negotiations for the use of CP/M on these broke down. IBM approached Microsoft's CEO, Bill Gates, who purchased QDOS from SCP allegedly for $50,000. This became Microsoft Disk Operating System, MS-DOS. Microsoft also licensed their system to multiple computer companies, who used their own names. Eventually, Microsoft would require the use of the MS -DOS name, with the exception of the IBM variant, which would continue to be developed concurrently and sold as PC-DOS (this was for IBM's new 'PC' using the 8088 CPU (internally the same as the 8086)).http://inventors.about.com/library/weekly/aa033099.htm

Digital Research would attempt to regain the market with DR-DOS, an MS-DOS and CP/M hybrid. Digital Research would later be bought out by Novell, and DR DOS became Novell DOS 7. DR DOS would later be part of Caldera (as OpenDOS), Lineo (as DR DOS), and DeviceLogics.

Early versions of Microsoft Windows were little more than a graphical Operating system shell for DOS, and later versions of Windows were tightly integrated with MS-DOS. It is also possible to run DOS programs under OS/2 and Linux using virtual-machine emulators. Because of the long existence and ubiquity of DOS in the world of the PC-compatible platform, DOS was often considered to be the native operating system of the PC compatible platform.

There are alternative versions of DOS, such as FreeDOS and OpenDOS. FreeDOS appeared in 1994 due to Microsoft Windows 95, which differed from Windows 3.11 by being not a shell and dispensing with MS-DOS.

Timeline Microsoft bought non-exclusive rights for marketing 86-DOS in October 1980. In July 1981, Microsoft bought exclusive rights for 86-DOS (by now up to version 1.14) and renamed the operating system MS-DOS.

The first IBM branded version, PC-DOS 1.0, was released in August, 1981. It supported up to 640 Kibibyte of RAM and four 160 kB 5.25" single sided floppy disks.

In May 1982, PC-DOS 1.1 added support for 320 kB double-sided floppy disks.

PC-DOS 2.0 and MS-DOS 2.0, released in March 1983, were the first versions to support the PC/XT and fixed disk drives (commonly referred to as hard disk drives). Floppy disk capacity was increased to 180 kB (single sided) and 360 kB (double sided) by using nine Disk sectors per track instead of eight.

At the same time, Microsoft announced its intention to create a GUI for DOS. Its first version, Windows 1.0, was announced on November 1983, but was unfinished and did not interest IBM. By November 1985, the first finished version, Microsoft Windows 1.01, was released.

MS-DOS 3.0, released in September 1984, first supported 1.2Mb floppy disks and 32Mb hard disks. MS-DOS 3.1, released November that year, introduced network support.

MS-DOS 3.2, released in April 1986, was the first retail release of MS-DOS. It added support of 720 kB 3.5" floppy disks. Previous versions had been sold only to computer manufacturers who pre-loaded them on their computers, because operating systems were considered part of a computer, not an independent product.

MS-DOS 3.3, released in April 1987, featured logical disks. A physical disk could be divided into several partitions, considered as independent disks by the operating system. Support was also added for 1.44 MB 3.5" floppy disks.

The first version of DR DOS was released in May of 1988, and was compatible with MS/PC-DOS 3.3. Later versions of DR DOS would continue to identify as "DOS 3.31." to applications, despite using newer version numbers.

MS-DOS 4.0, released in July 1988, supported disks up to 2 GB (disk sizes were typically 40-60 MB in 1988), and added a full-screen shell called DOS Shell. Other shells, like Norton Commander and PCShell, already existed in the market. In November of 1988, Microsoft addressed many bugs in a service release, MS-DOS 4.01.

DR DOS skipped version 4 due to perceived unpopularity of MS-DOS 4.x. Wishing to get a jump on Microsoft, Digital Research released DR DOS 5 in May 1990, which included much more powerful utilities that previous DOS versions.

MS-DOS 5.0 was released in April 1991, mainly as a follow-up to DR DOS 5. It included the full-screen BASIC interpreter QBasic, which also provided a full-screen text editor (previously, MS-DOS had only a line-based text editor, edlin). A disk cache utility SmartDrive, undelete capabilities, and other improvements were also included. It had severe problems with some disk utilities, fixed later in MS-DOS 5.01, released later in the same year.

DR DOS 6.0 was released in 1991.

In March 1992, Microsoft released Windows 3.1, which became the first popular version of Microsoft Windows, with more than 1,000,000 purchasing the graphical user interface. A section of the Windows 3.1 beta installer (the "AARD code") caused the installation to fail on non-Microsoft DOS systems, including DR DOS. This led to a decline in the use of DR DOS.

MS-DOS 6.0 was released in March 1993. Following competition from Digital Research's SuperStor, Microsoft added a disk compression utility called DoubleSpace. At the time, typical hard disk sizes were about 200-400 MB, and many users badly needed more disk space. It turned out that DoubleSpace contained stolen code from another compression utility, Stacker, which led to later legal problems. MS-DOS 6.0 also featured the disk defragmenter DEFRAG, backup program MSBACKUP, memory optimization with List of DOS commands#memmaker, and rudimentary virus protection via MSAV.

As with versions 4.0 and 5.0, MS-DOS 6.0 turned out to be buggy. Due to complaints about loss of data, Microsoft released an updated version, MS-DOS 6.2, with an improved DoubleSpace utility, a new disk check utility, SCANDISK (similar to fsck from Unix), and other improvements.

December 1993 saw the release of Novell DOS 7, which was DR DOS under a new name. Its multiple bugs, as well as DR DOS' already declining market share and Windows 95 looming on the horizon, led to low sales.http://www.ug.bcc.bilkent.edu.tr/~farukg/yazilar/histwindows.htm By this time, PC DOS was at version 6.1, and IBM split its development from Microsoft. From this point, the two developed independently.

The next version of MS-DOS, 6.21 (released March 1994), appeared due to legal problems. Stac Electronics sued Microsoft due to stolen source code from their utility, Stacker, and forced them to remove DoubleSpace from their operating system.

In May 1994, Microsoft released MS-DOS 6.22, with another disk compression package, DriveSpace, licensed from VertiSoft Systems.

MS-DOS 6.22 was the last stand-alone version of MS-DOS available to the general public. MS-DOS was removed from marketing by Microsoft on November 30, 2001. http://www.microsoft.com/windows/lifecycle/default.mspx Microsoft Licensing Roadmap

Microsoft also released versions 6.23 to 6.25 for banks and American military organizations. These versions introduced File Allocation Table support. Microsoft Windows 95 incorporated MS-DOS version 7.0, but only as the kernel (as Windows became the full operating system). Windows 98 also used MS-DOS 7. At this point, Microsoft announced abandonment of the DOS kernel and released Windows 2000 on the NT kernel, but following its commercial failure, released one more DOS kernel Windows, Windows ME. The next system, Windows XP, was based on the NT kernel. Windows ME used MS-DOS 8; Windows XP and Vista continue to use MS-DOS 8 on emergency startup disks.

IBM released PC-DOS 7.0 in early 1995. It incorporated many new utilities such as anti-virus software, comprehensive backup programs, PCMCIA support, and DOS Pen extensions. Also added were new features to enhance available memory and disk space. The last version of PC DOS was PC DOS 2000, released in 1998. Its major feature was Y2K compatibility.

Following Novell DOS 7, Novell sold DR DOS to Caldera, who released it as the open sourced "OpenDOS". It would later be transferred to a branch company, Lineo, who released another version as DR DOS 7. Lineo sold DR DOS to another company, DeviceLogics, who has not released any newer versions. The source of OpenDos is developed separately, and is called "Enhanced DR DOS."

Accessing hardware under DOS The operating system offers a hardware abstraction layer that allows development of character-based applications, but not for accessing most of the computer hardware, such as Video cards, computer printers, or computer mouse. This required programmers to access the hardware directly, resulting in each application having its own set of device drivers for each hardware peripheral. Hardware manufacturers would release specifications to ensure device drivers for popular applications were available.

DOS and other PC operating systems Early versions of Microsoft Windows were shell programs that ran in DOS. Windows 3.11 extended the shell by going into protected mode and added 32-bit support. These were 16-bit/32-bit hybrids. Microsoft Windows 95 further reduced DOS to the role of the bootloader. Windows 98 and Windows Me were the last Microsoft OS to run on DOS. The DOS-based branch was eventually abandoned in favor of Windows NT, the first true 32-bit system that was the foundation for Windows XP and Windows Vista.

Windows NT, initially NT OS/2 3.0, was the result of a collaboration between Microsoft and IBM to develop a 32-bit operating system that had high hardware and software portability. Because of the success of Windows 3.0, Microsoft changed the application programming interface to the extended Windows API, which caused a split between the two companies and a branch in the operating system. IBM would continue to work on OS/2 and OS/2 API, while Microsoft renamed its operating system Windows NT.

Reserved device names under DOS There are reserved device names in DOS that cannot be used as filenames regardless of extension; these restrictions also affect several Windows versions, in some cases causing crashes and security vulnerabilities.

A partial list of these reserved names is: NUL:, COM1: or AUX:, COM2:, COM3:, COM4:, CON:, LPT1: or PRN:, LPT2:, LPT3:, and CLOCK$.

More recent versions of both MS-DOS and IBM-DOS allow reserved device names without the trailing colon; e.g., PRN refers to PRN:.

The NUL filename redirects to a null file, similar in function to the UNIX device /dev/null. It is best suited for being used in batch command files to discard unneeded output. If NUL is copied to a file that already exists, it will truncate the target file; otherwise, a zero byte file will be created. (Thus, copy NUL foo is functionally similar to the UNIX commands cat foo and cp /dev/null foo.) Naming a file as NUL, regardless of extension, could cause unpredictable behavior in most applications. Well-designed applications will generate an error stating that NUL is a DOS reserved filename; others generate the file but whatever the program saves is lost; finally, some applications may hang or leave the computer in an inconsistent state, requiring a Reboot (computer).

Drive naming scheme Under Microsoft's DOS operating system and its derivatives drives are referred to by identifying letters. Standard practice is to reserve "A" and "B" for floppy drives. On systems with only one floppy drive DOS permits the use of both letters for one drive, and DOS will ask to swap disks. This permits copying from floppy to floppy or having a program run from one floppy while having its data on another. Hard drives were originally assigned the letters "C" and "D". DOS could only support one active partition per drive. As support for more hard drives became available, this developed into assigning the active primary partition on each drive letters first, then making a second pass over the drives to allocate letters to logical drives in the extended partition, then making a third, which gives the other non-active primary partitions their names. (Always assumed, they exist and contain a DOS-readable file system.) Lastly, DOS allocate letters for optical disc drives, RAM disks and other hardware. Letter assignments usually occur in the order of the drivers loaded, but the drivers can instruct DOS to assign a different letter. An example is network drives, for which the driver will assign letters nearer the end of the alphabets.

Because DOS applications use these drive letters directly (unlike the /dev folder in Unix-like systems), they can be disrupted by adding new hardware that needs a drive letter. An example is the addition of a new hard drive with a primary partition to an original hard drive that contains logical drives in extended partitions. As primary partitions have higher priority than the logical drives, it will change drive letters in the configuration. Moreover, attempts to add a new hard drive with only logical drives in an extended partition would still disrupt the letters of RAM disks and optical drives. This problem persisted through the 9x versions of Windows until NT, which preserves the letters of existing drives until the user changes it.

The DOS boot sequence The boot information for PC-compatible computers is located at track zero. In DOS, this code will read the DOS BIOS into memory and execute it. The BIOS is located in IBMBIO.COM on DR DOS and PC DOS, and IO.SYS on MS DOS. The BIOS will then load the DOS kernel, located in IBMDOS.COM (PC DOS or DR DOS) or MSDOS.SYS (MS DOS). In the Windows DOS versions (MS DOS 7 and 8), the BIOS and kernel are combined in IO.SYS, and MSDOS.SYS is a text configuration file.

The kernel then executes the CONFIG.SYS file. In CONFIG.SYS, the SHELL command specifies the location of the shell (typically COMMAND.COM). The shell will then launch, and open a startup batch file (typically AUTOEXEC.BAT)

DOS emulators Under Linux it is possible to run copies of DOS and many of its clones under DOSEMU, a Linux-native virtual machine for running real mode programs. There are a number of other emulators for running DOS under various versions of UNIX, even on non-x86 platforms, such as DOSBox

DOS emulators are gaining popularity among Windows XP users because Windows XP system is incompatible with pure DOS. They are used to play 'abandonware' made for DOS. One of the most famous emulators is DOSBox, designed for game-playing on modern operating systems. Another emulator ExDOS is designed for business. VDMSound is also popular on Windows XP for its GUI and sound support.

See also

References External links

command.DOS (from Disk Operating System) commonly refers to the family of closely related operating systems which dominated the IBM PC compatible market between 1981 and 1995 (or until about 2000, if Windows 9x systems are included): DR-DOS, FreeDOS, MS-DOS, Novell-DOS, OpenDOS, PC-DOS, PTS-DOS, ROM-DOS and several others. They are single user, single task systems. MS-DOS from Microsoft was the most widely used. These operating systems ran on IBM PC type hardware using the Intel x86 CPUs or their compatible cousins from other makers. MS-DOS, inspired by CP/M, is still common today and was the foundation for many of Microsoft's operating systems (from Windows 1.0 through Windows Me). MS-DOS was later used as the foundation for their operating systems.

History MS-DOS (and the IBM PC-DOS which was licensed therefrom), and its predecessor, 86-DOS, was inspired by CP/M (Control Program /(for) Microcomputers) — which was the dominant disk operating system for 8-bit Intel 8080 and Zilog Zilog Z-80 based microcomputers. Tim Paterson at Seattle Computer Products developed a variant of CP/M-80, intended as an internal product for testing the SCP's new 8086 Central processing unit card for the S-100 bus. It did not run on the 8080 CPU needed for CP/M-80. The system was named 86-DOS (it had initially been called QDOS, which stood for Quick and Dirty Operating System).

A full time operating system was needed for IBM's 8086 line of computers, but negotiations for the use of CP/M on these broke down. IBM approached Microsoft's CEO, Bill Gates, who purchased QDOS from SCP allegedly for $50,000. This became Microsoft Disk Operating System, MS-DOS. Microsoft also licensed their system to multiple computer companies, who used their own names. Eventually, Microsoft would require the use of the MS -DOS name, with the exception of the IBM variant, which would continue to be developed concurrently and sold as PC-DOS (this was for IBM's new 'PC' using the 8088 CPU (internally the same as the 8086)).http://inventors.about.com/library/weekly/aa033099.htm

Digital Research would attempt to regain the market with DR-DOS, an MS-DOS and CP/M hybrid. Digital Research would later be bought out by Novell, and DR DOS became Novell DOS 7. DR DOS would later be part of Caldera (as OpenDOS), Lineo (as DR DOS), and DeviceLogics.

Early versions of Microsoft Windows were little more than a graphical Operating system shell for DOS, and later versions of Windows were tightly integrated with MS-DOS. It is also possible to run DOS programs under OS/2 and Linux using virtual-machine emulators. Because of the long existence and ubiquity of DOS in the world of the PC-compatible platform, DOS was often considered to be the native operating system of the PC compatible platform.

There are alternative versions of DOS, such as FreeDOS and OpenDOS. FreeDOS appeared in 1994 due to Microsoft Windows 95, which differed from Windows 3.11 by being not a shell and dispensing with MS-DOS.

Timeline Microsoft bought non-exclusive rights for marketing 86-DOS in October 1980. In July 1981, Microsoft bought exclusive rights for 86-DOS (by now up to version 1.14) and renamed the operating system MS-DOS.

The first IBM branded version, PC-DOS 1.0, was released in August, 1981. It supported up to 640 Kibibyte of RAM and four 160 kB 5.25" single sided floppy disks.

In May 1982, PC-DOS 1.1 added support for 320 kB double-sided floppy disks.

PC-DOS 2.0 and MS-DOS 2.0, released in March 1983, were the first versions to support the PC/XT and fixed disk drives (commonly referred to as hard disk drives). Floppy disk capacity was increased to 180 kB (single sided) and 360 kB (double sided) by using nine Disk sectors per track instead of eight.

At the same time, Microsoft announced its intention to create a GUI for DOS. Its first version, Windows 1.0, was announced on November 1983, but was unfinished and did not interest IBM. By November 1985, the first finished version, Microsoft Windows 1.01, was released.

MS-DOS 3.0, released in September 1984, first supported 1.2Mb floppy disks and 32Mb hard disks. MS-DOS 3.1, released November that year, introduced network support.

MS-DOS 3.2, released in April 1986, was the first retail release of MS-DOS. It added support of 720 kB 3.5" floppy disks. Previous versions had been sold only to computer manufacturers who pre-loaded them on their computers, because operating systems were considered part of a computer, not an independent product.

MS-DOS 3.3, released in April 1987, featured logical disks. A physical disk could be divided into several partitions, considered as independent disks by the operating system. Support was also added for 1.44 MB 3.5" floppy disks.

The first version of DR DOS was released in May of 1988, and was compatible with MS/PC-DOS 3.3. Later versions of DR DOS would continue to identify as "DOS 3.31." to applications, despite using newer version numbers.

MS-DOS 4.0, released in July 1988, supported disks up to 2 GB (disk sizes were typically 40-60 MB in 1988), and added a full-screen shell called DOS Shell. Other shells, like Norton Commander and PCShell, already existed in the market. In November of 1988, Microsoft addressed many bugs in a service release, MS-DOS 4.01.

DR DOS skipped version 4 due to perceived unpopularity of MS-DOS 4.x. Wishing to get a jump on Microsoft, Digital Research released DR DOS 5 in May 1990, which included much more powerful utilities that previous DOS versions.

MS-DOS 5.0 was released in April 1991, mainly as a follow-up to DR DOS 5. It included the full-screen BASIC interpreter QBasic, which also provided a full-screen text editor (previously, MS-DOS had only a line-based text editor, edlin). A disk cache utility SmartDrive, undelete capabilities, and other improvements were also included. It had severe problems with some disk utilities, fixed later in MS-DOS 5.01, released later in the same year.

DR DOS 6.0 was released in 1991.

In March 1992, Microsoft released Windows 3.1, which became the first popular version of Microsoft Windows, with more than 1,000,000 purchasing the graphical user interface. A section of the Windows 3.1 beta installer (the "AARD code") caused the installation to fail on non-Microsoft DOS systems, including DR DOS. This led to a decline in the use of DR DOS.

MS-DOS 6.0 was released in March 1993. Following competition from Digital Research's SuperStor, Microsoft added a disk compression utility called DoubleSpace. At the time, typical hard disk sizes were about 200-400 MB, and many users badly needed more disk space. It turned out that DoubleSpace contained stolen code from another compression utility, Stacker, which led to later legal problems. MS-DOS 6.0 also featured the disk defragmenter DEFRAG, backup program MSBACKUP, memory optimization with List of DOS commands#memmaker, and rudimentary virus protection via MSAV.

As with versions 4.0 and 5.0, MS-DOS 6.0 turned out to be buggy. Due to complaints about loss of data, Microsoft released an updated version, MS-DOS 6.2, with an improved DoubleSpace utility, a new disk check utility, SCANDISK (similar to fsck from Unix), and other improvements.

December 1993 saw the release of Novell DOS 7, which was DR DOS under a new name. Its multiple bugs, as well as DR DOS' already declining market share and Windows 95 looming on the horizon, led to low sales.http://www.ug.bcc.bilkent.edu.tr/~farukg/yazilar/histwindows.htm By this time, PC DOS was at version 6.1, and IBM split its development from Microsoft. From this point, the two developed independently.

The next version of MS-DOS, 6.21 (released March 1994), appeared due to legal problems. Stac Electronics sued Microsoft due to stolen source code from their utility, Stacker, and forced them to remove DoubleSpace from their operating system.

In May 1994, Microsoft released MS-DOS 6.22, with another disk compression package, DriveSpace, licensed from VertiSoft Systems.

MS-DOS 6.22 was the last stand-alone version of MS-DOS available to the general public. MS-DOS was removed from marketing by Microsoft on November 30, 2001. http://www.microsoft.com/windows/lifecycle/default.mspx Microsoft Licensing Roadmap

Microsoft also released versions 6.23 to 6.25 for banks and American military organizations. These versions introduced File Allocation Table support. Microsoft Windows 95 incorporated MS-DOS version 7.0, but only as the kernel (as Windows became the full operating system). Windows 98 also used MS-DOS 7. At this point, Microsoft announced abandonment of the DOS kernel and released Windows 2000 on the NT kernel, but following its commercial failure, released one more DOS kernel Windows, Windows ME. The next system, Windows XP, was based on the NT kernel. Windows ME used MS-DOS 8; Windows XP and Vista continue to use MS-DOS 8 on emergency startup disks.

IBM released PC-DOS 7.0 in early 1995. It incorporated many new utilities such as anti-virus software, comprehensive backup programs, PCMCIA support, and DOS Pen extensions. Also added were new features to enhance available memory and disk space. The last version of PC DOS was PC DOS 2000, released in 1998. Its major feature was Y2K compatibility.

Following Novell DOS 7, Novell sold DR DOS to Caldera, who released it as the open sourced "OpenDOS". It would later be transferred to a branch company, Lineo, who released another version as DR DOS 7. Lineo sold DR DOS to another company, DeviceLogics, who has not released any newer versions. The source of OpenDos is developed separately, and is called "Enhanced DR DOS."

Accessing hardware under DOS The operating system offers a hardware abstraction layer that allows development of character-based applications, but not for accessing most of the computer hardware, such as Video cards, computer printers, or computer mouse. This required programmers to access the hardware directly, resulting in each application having its own set of device drivers for each hardware peripheral. Hardware manufacturers would release specifications to ensure device drivers for popular applications were available.

DOS and other PC operating systems Early versions of Microsoft Windows were shell programs that ran in DOS. Windows 3.11 extended the shell by going into protected mode and added 32-bit support. These were 16-bit/32-bit hybrids. Microsoft Windows 95 further reduced DOS to the role of the bootloader. Windows 98 and Windows Me were the last Microsoft OS to run on DOS. The DOS-based branch was eventually abandoned in favor of Windows NT, the first true 32-bit system that was the foundation for Windows XP and Windows Vista.

Windows NT, initially NT OS/2 3.0, was the result of a collaboration between Microsoft and IBM to develop a 32-bit operating system that had high hardware and software portability. Because of the success of Windows 3.0, Microsoft changed the application programming interface to the extended Windows API, which caused a split between the two companies and a branch in the operating system. IBM would continue to work on OS/2 and OS/2 API, while Microsoft renamed its operating system Windows NT.

Reserved device names under DOS There are reserved device names in DOS that cannot be used as filenames regardless of extension; these restrictions also affect several Windows versions, in some cases causing crashes and security vulnerabilities.

A partial list of these reserved names is: NUL:, COM1: or AUX:, COM2:, COM3:, COM4:, CON:, LPT1: or PRN:, LPT2:, LPT3:, and CLOCK$.

More recent versions of both MS-DOS and IBM-DOS allow reserved device names without the trailing colon; e.g., PRN refers to PRN:.

The NUL filename redirects to a null file, similar in function to the UNIX device /dev/null. It is best suited for being used in batch command files to discard unneeded output. If NUL is copied to a file that already exists, it will truncate the target file; otherwise, a zero byte file will be created. (Thus, copy NUL foo is functionally similar to the UNIX commands cat foo and cp /dev/null foo.) Naming a file as NUL, regardless of extension, could cause unpredictable behavior in most applications. Well-designed applications will generate an error stating that NUL is a DOS reserved filename; others generate the file but whatever the program saves is lost; finally, some applications may hang or leave the computer in an inconsistent state, requiring a Reboot (computer).

Drive naming scheme Under Microsoft's DOS operating system and its derivatives drives are referred to by identifying letters. Standard practice is to reserve "A" and "B" for floppy drives. On systems with only one floppy drive DOS permits the use of both letters for one drive, and DOS will ask to swap disks. This permits copying from floppy to floppy or having a program run from one floppy while having its data on another. Hard drives were originally assigned the letters "C" and "D". DOS could only support one active partition per drive. As support for more hard drives became available, this developed into assigning the active primary partition on each drive letters first, then making a second pass over the drives to allocate letters to logical drives in the extended partition, then making a third, which gives the other non-active primary partitions their names. (Always assumed, they exist and contain a DOS-readable file system.) Lastly, DOS allocate letters for optical disc drives, RAM disks and other hardware. Letter assignments usually occur in the order of the drivers loaded, but the drivers can instruct DOS to assign a different letter. An example is network drives, for which the driver will assign letters nearer the end of the alphabets.

Because DOS applications use these drive letters directly (unlike the /dev folder in Unix-like systems), they can be disrupted by adding new hardware that needs a drive letter. An example is the addition of a new hard drive with a primary partition to an original hard drive that contains logical drives in extended partitions. As primary partitions have higher priority than the logical drives, it will change drive letters in the configuration. Moreover, attempts to add a new hard drive with only logical drives in an extended partition would still disrupt the letters of RAM disks and optical drives. This problem persisted through the 9x versions of Windows until NT, which preserves the letters of existing drives until the user changes it.

The DOS boot sequence The boot information for PC-compatible computers is located at track zero. In DOS, this code will read the DOS BIOS into memory and execute it. The BIOS is located in IBMBIO.COM on DR DOS and PC DOS, and IO.SYS on MS DOS. The BIOS will then load the DOS kernel, located in IBMDOS.COM (PC DOS or DR DOS) or MSDOS.SYS (MS DOS). In the Windows DOS versions (MS DOS 7 and 8), the BIOS and kernel are combined in IO.SYS, and MSDOS.SYS is a text configuration file.

The kernel then executes the CONFIG.SYS file. In CONFIG.SYS, the SHELL command specifies the location of the shell (typically COMMAND.COM). The shell will then launch, and open a startup batch file (typically AUTOEXEC.BAT)

DOS emulators Under Linux it is possible to run copies of DOS and many of its clones under DOSEMU, a Linux-native virtual machine for running real mode programs. There are a number of other emulators for running DOS under various versions of UNIX, even on non-x86 platforms, such as DOSBox

DOS emulators are gaining popularity among Windows XP users because Windows XP system is incompatible with pure DOS. They are used to play 'abandonware' made for DOS. One of the most famous emulators is DOSBox, designed for game-playing on modern operating systems. Another emulator ExDOS is designed for business. VDMSound is also popular on Windows XP for its GUI and sound support.

See also

References External links



DOS from FOLDOC
DOS < operating system > 1. The common abbreviation for MS-DOS. 2. IBM 's Disk Operating System. 3. Any disk operating system. (2001-03-16) Try this search on Wikipedia, OneLook ...

Microsoft Disk Operating System from FOLDOC
MS-DOS ==> Microsoft Disk Operating System < operating system > /M S doss/ (Or "MS-DOS", "PC-DOS", "MS-DOG", "mess-dos") Microsoft Corporation 's clone of the CP/M disk operating ...

dos.co.uk
Ingram Micro Launches Service Identifying Green Computer Products Aug. 5, 2008. Ingram Micro Appoints John Soumbasakis to Senior Vice ...

dos.co.uk

DOS - Wikipedia, the free encyclopedia
DOS is a family of closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995 (or until about 2000, if one includes DOS-based Microsoft ...

MS-DOS - Wikipedia, the free encyclopedia
MS-DOS (short for M icro s oft D isk O perating S ystem) is an operating system commercialized by Microsoft. It was the most commonly used member of the DOS family of operating ...

DOS Solutions
DOS Solutions, information, links, downloads, programs, utilities, networking, internet, lans, ethernet, progamming, vbdos, embedded DOS, thinclient, eznos, etc for DOS(disk ...

NukeSoft MS-DOS Reference
Contains information about using commands included with DOS and a detailed history of DOS.

MS-DOS History
MS-DOS History. Home >> MS-DOS Reference >> MS-DOS Versions. The history of MS-DOS is surprisingly long. It started off as QDOS (Quick and Dirty Operating System) which was ...

DOS Emulation on Linux (PreshWeb)
Using DOSEMU to run classic DOS games under Linux - a simple guide. ... DOS Emulation Under Linux . With just a little work, it's possible to get your Linux system to run DOS ...

 

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