Atari Operating Systems

The Atari 8-bit range of computers came with an operating system built into ROM.

The original Atari 400 and 800 came with:

  • Atari OS Revision A (10K ROM on 3 seperate chips) - early machines only
  • Atari OS Revision B (10K ROM on 3 seperate chips) - contained bug fixes, most 400s and 800s had this Rev. B.

Later, the XL/XE-series got more operating system revisions to support additional onboard hardware and peripherals, although this caused some compatibility issues with older software. To compensate for this incompatibility, Atari made the 'Translator Disk', a floppy disk which loaded the older 400/800 Revision A or B operating system into XL and XE computers.

For the XL/XE-series, the following operating systems were shipped:

  • Atari OS Revision 10 (16K ROM on 2 chips) - came on the 1200XL Revision A
  • Atari OS Revision 11 (16K ROM on 2 chips) - came on the 1200XL Revision B, contained bug fixes
  • Atari OS Revision 1 (16K ROM) - came on the 600XL
  • Atari OS Revision 2 (16K ROM) - came on the 800XL
  • Atari OS Revision 3 (16K ROM) - came on the 800XE and 130XE
  • Atari OS Revision 4 (32K ROM - 16K OS, 8K BASIC, 8K Missile Command) - came on the XEGS



The XL/XE-series came with Atari BASIC built into ROM. Early models were shipped with the notoriously buggy Revision B, while later models came with Revision C.



Atari Disk Operating Systems

Several floppy disk drives were made available for the Atari 8-bit computers. To support disk operations, the built-in operating system contained only very low-level routines. An extra Disk Operating System (DOS) had to be loaded to perform more fundamental tasks with disk access. This Disk Operating System was called "Atari DOS", and this had to be booted from floppy disk every time the computer was switched on. Unlike most other DOSs of the time, Atari DOS was entirely menu-driven.

The different versions of Atari DOS are:

  • Atari DOS 1.0 - the first version.
  • Atari DOS 2.0S/D - improved version over 1.0, 2.0S became the standard for the Atari 810 Floppy Disk Drive. 2.0D was planned for the Atari 815 Floppy Disk Drive, which was never released.
  • Atari DOS 3.0 - came with the Atari 1050 Floppy Disk Drive. Used a different disk format to previous releases, thus incompatible with them.
  • Atari DOS 2.5 - came with later Atari 1050 Floppy Disk Drives, replaced DOS 3.0. Functionally the same but added support for Enhanced Density disks.
  • Atari DOS 4.0 - designed for Atari 1450XLD which was never released.
  • Atari DOS XE - designed for the Atari XF551 Floppy Disk Drive.