DOS was originally designed to load an operating system from a floppy disk to a computer with no hard drive (before hard drives were common). Today, any reference to DOS is synonymous with MS-DOS.
The following table provides a version history of MS-DOS.
|1.0||August 1981||Distributed on one floppy disk (required 8 KB of RAM).|
|1.1||May 1982||Added supported for 320-KB double-sided disks.|
|2.0||March 1983||Introduced support for hard disks, directories, background printing, and the ability to add device drivers.|
|3.0||August 1984||Increased support for hard disks larger than 10 MB and 1.2-MB floppy disks.|
|3.1||March 1985||Added networks and file sharing.|
|3.2||January 1986||Included support for 3.5-inch floppy disks.|
|3.3||April 1987||Added new commands and international support.|
|4.0||February 1988||Added support for hard disks greater than 32 MB, the MEM command, and MS-DOS Shell.|
|5.0||May 1991||Added memory management tools, help, undelete, unformat, task swapping. This was the last version to come with a printed manual.|
|6.0||March 1993||Included new features such as MEMMAKER, multiple boot configurations, Windows UNFORMAT and UNDELETE, virus protection, and backup. MEMMAKER is a utility that is used to modify the system's CONFIG.SYS and AUTOEXEC.BAT files, so that device drivers and memory-resident programs take up less conventional memory space.|
|6.2||October 1993||Included ScanDisk, MSD utilities, enhanced diagnostics.|
|7.0||December 1995||Not really a stand-alone product; provided the command-level environment included with Windows 95.|
Some computer manufacturers have produced OEM (original equipment manufacturer) versions of MS-DOS. For the most part, these versions have been cosmetically modified for specific use with their computers (such as a "splash screen" that shows the company logo during boot up). Care should be taken when using any computer with one of these operating systems-some incompatibilities with software written for MS-DOS might exist. You should be careful when substituting a generic DOS for MS-DOS if you are reformatting a hard disk drive or reinstalling the operating system. Make such a substitution only after you have verified that the generic version is compatible with all of the computer's hardware and software; the generic version might not provide the necessary support.
MS-DOS includes three programs that are required to make a drive or floppy disk bootable:
IO.SYS: The interface between the hardware and the operating-system code
MSDOS.SYS: The main operating-system code
COMMAND.COM: The interface between the user and the operating-system code
IO.SYS and MSDOS.SYS are hidden files that are not usually visible when you examine a disk directory.
In addition to the three core files, MS-DOS uses two other startup files. These files are not required to start the machine, but they add any additional startup configuration required by the user or applications. These files are:
CONFIG.SYS: Loads extra hardware and device drivers not built into the IO.SYS.
AUTOEXEC.BAT: Loads terminate-and-stay-resident (TSR) programs selected by the user and sets up the environment variables such as TEMP and PATH.
If a user complains that a machine is not loading MS-DOS, especially after installing new hardware or software, disable these two files as a first diagnostic step. In many cases, drivers or procedure calls are conflicting or corrupting system memory.