Difference between revisions of "Ms technology vocabulary DOS"

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'Wainaina' Wanguri

January 2009

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http://wiki.sjs.org/wiki/index.php/MS_Technology_Vocabulary

DOS, short for "Disk Operating System",[1] is a shorthand term for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions Windows 95, 98, and Me.

All DOS-type operating systems run on machines with the Intel x86 or compatible CPUs, mainly the IBM PC and compatibles. Initially, DOS was not restricted to these, and machine-dependent versions of DOS and similar operating systems were produced for many non-IBM-compatible x86-based machines.[2]

DOS is a single-user, single-task operating system with basic kernel functions that are non-reentrant: only one program at a time can use them. There is an exception with Terminate and Stay Resident (TSR) programs, and some TSRs can allow multitasking. However, there is still a problem with the non-reentrant kernel: once a process calls a service inside of operating system kernel (system call), it must not be interrupted with another process calling system call, until the first call is finished.[3]

The DOS kernel provides various functions for programs, like displaying characters on-screen, reading a character from the keyboard, accessing disk files and more.

In DOS, 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.[8]

Because DOS applications use these drive letters directly (unlike the /dev directory 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.[8]

While DOS was the primary PC-compatible platform, several notable programs were written for it. These included:

   * Lotus 1-2-3; a spreadsheet program that saw heavy use in corporate markets, and has been credited with the success of the IBM PC[27]
   * WordPerfect; a word processor that is currently produced for the Windows platform
   * dBase; one of the earliest database programs
   * Telix; a modem communication program
   * Arachne; a DOS web browser
   * DJGPP, the DOS port of gcc
   * 4DOS, a replacement shell
   * Borland's integrated development environment, which included Turbo Pascal, Turbo BASIC, Turbo C, and Turbo Assembler
   * BBS hosting software RemoteAccess, Spitfire, Maximus, McBBS, and TAG
   * BASIC-language utilities BASICA and GW-BASIC
   * Numerous first-person shooter games: Wolfenstein 3D, a joint venture between ID Software and Apogee Software (later 3D Realms); ID Software's Doom and Quake; and 3D Realms' Duke Nukem 3D, Shadow Warrior, and Rise of the Triad. All three 3D Realms' titles were built with the DOS-based Build engine, written by Ken Silverman and used for Silverman's Ken's Labyrinth.

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