IBM Disk BASIC 1.10
Appeared in 1981
Developer Microsoft (for IBM)
Influenced by IBM Cassette BASIC

IBM Disk BASIC was a version of the Microsoft BASIC programming language licensed by IBM for the IBM PC DOS. It was included in the original IBM PC DOS and required the original IBM PC BIOS to run. The name Disk BASIC came from its use of floppy disks rather than cassette tapes to store programs and data. GW BASIC is a standalone compatible successor of IBM Disk BASIC that doesn't require the original IBM PC BIOS to run. A later version IBM BASICA (short for "Advanced BASIC") added features to support graphics, sound (on the built-in speaker), and event handling for communications and joystick presses. Neither version of IBM BASIC would run on on non-IBM computers or later IBM models, since those lack the needed ROM BASIC; the equivalent to BASICA for non-IBM MS DOS compatible computers was GW-BASIC.


BASIC was loaded when its name was typed at a command prompt, with some optional parameters to control allocation of memory. When loaded, it displayed a sign-on identification message and started a full-screen text editor. The function keys were assigned common commands, which were displayed at the bottom of the screen. Commands could be typed in to load and save programs, and expressions could be typed in and executed in immediate mode. If a line of input started with a number, the language system stored the following line of text as part of program source. When listed on screen, lines were displayed in order of increasing line number. Changes could be made to a displayed line of program source code by moving the cursor to the line with the cursor keys, and typing over the on-screen text. Program source was stored internally in a tokenized form, where keywords were replaced with a single byte token, to save space and save execution time. Programs could be saved in compact tokenized form, or optionally saved as DOS text ASCII files that could be viewed and edited with other programs. Like most other MS DOS applications, BASICA was a text-mode program and had no features for windows, icons, mouse support, or cut and paste editing.


IBM personal computers came with several versions of BASIC. Cassette BASIC was built into the BIOS ROMs of the original PC and XT, and early models in the PS/2 line. It only supported a cassette tape interface for loading and saving programs, which was unavailable on models after the original Model 5150. Disk BASIC (BASIC.COM) added functions to use files on diskette, and also supported the serial port. It made use of the cassette BASIC ROM software and so would not run on machines not equipped with the IBM ROMs. Advanced BASIC (BASICA.COM) provided event trapping, extended support for monophonic sound (using the PC's built-in speaker), and graphics functions to set and clear pixels, draw lines and circles, and set colors. Advanced BASIC also required the casssette ROMs to function. A cartridge version of BASIC was only available on the IBM PCjr and supported the additional graphics modes and sounds possible on that platform.[1]

GW-BASIC was a Microsoft product distributed with non-IBM MS DOS computers, and supported all the graphics modes and features of BASICA on computers that did not have the IBM cassette BASIC.

The successor to BASICA for MS-DOS and PC-DOS versions was QBasic, which was a stripped-down version of the Microsoft QuickBASIC compiler that could not save executable files.


  1. ^ Computer! Magazine, No. 78, November 1986 p. 8, retrieved February 23, 2011

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