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The Operating System (TOS)[1] is the operating system of the Atari ST range of computers. This range includes the 520ST, 1040ST and the F, FM and E variations (e.g.1040STE). Later, 32-bit machines (TT, Falcon030) were developed using a new version of TOS, called MultiTOS, which allowed multitasking. More recently, users have developed TOS further into FreeMiNT.



The Atari TOS debuted with the Atari 520ST in 1985. TOS combines Digital Research's GEM GUI running on top of the DOS-like GEMDOS. Features include a flat memory model, MS-DOS-compatible disk format, support for MIDI, and a variant of SCSI called ACSI in later versions. Atari's TOS is run from ROM chips contained in the computer, thus before local hard drives were available in home computers it was an almost instant-running OS. TOS originally booted off floppy disks but later ST models came with the latest version of TOS in ROM.[2]

TOS consisted of the following:

  • Desktop - The main interface loaded after bootup.
  • GEM - Graphical Environment Manager
    • AES - Application Environment Service
    • VDI - Virtual Device Interface (screen drivers only, other drivers loaded using GDOS)
  • GEMDOS - GEM Disk Operating System
  • BIOS - Basic Input/Output System
  • XBIOS - Xtended BIOS
  • Line-A - Low-level high-speed graphics calls. Obsolete

The following were extensions to TOS (loaded separately):

  • GDOS - Graphics Device Operation System
  • AHDI - Atari Hard Disk Interface (driver for Hard Drive)

True multitasking was not directly supported, TOS allows desk accessories to be loaded into the system which are similar to TSRs (Terminate and Stay Resident) on PCs (up to a maximum of six) and could co-operatively multitask. MultiTOS was developed to allow TOS to preemptively multitask.



Atari TOS/GEM - Monochrome screen

The TOS desktop uses icons to represent files and devices, windows and dialog boxes to display info. The desktop file "DESKTOP.INF" was read to determine window settings, icon placements and drive icons, otherwise the standard default desktop of two floppy icons and the trash icon was used.

Later versions use "NEWDESK.INF" for saving and reading the desktop configuration.

Executable files are identified by their extensions:

  • *.ACC - Desktop accessory. Automatically loaded.
  • *.APP - Application (not common).
  • *.PRG - Executable program. Can be GEM programs.
  • *.TOS - "TOS" program that doesn't use GEM. The desktop clears the screen, turns on the text cursor and hides the mouse cursor.
  • *.TTP - "TOS takes parameters". This opens a dialog box where arguments can be added for the program. However, it converts characters to uppercase.

TOS programs (but not GEM programs) can auto boot by placing them in a folder named "AUTO". TOS 1.4 allows GEM programs to be set to load automatically from the "Install Application" dialog. Programs with *.TTP extensions and environments can not be used for auto boot. Desktop accessories were placed in the root directory of the default drive and loaded automatically.



  • 1.0 (ROM TOS) Earliest version released on disk. First ROM release of TOS.
    • Formats: floppy, 2 chip and 6 chip ROMs (192 KB)
    • Rom date: 20 Nov 1985
    • Machines: 520ST, 1040ST
  • 1.02 (MEGA TOS) fixed bugs, supported Blitter co-processor and real-time clock.
    • Formats: 2 chip and 6 chip ROMs (192 KB)
    • Rom date: 22 Apr 1987
    • Machines: 520ST, 1040ST, Mega 2, Mega 4
  • 1.04 (RAINBOW TOS) Many bug fixes, file selector changed, DOS-compatible disk formatting, much improved performance. However, compatibility problems with older software.
    • Formats: 2 chip and 6 chip ROMs (192 KB)
    • Rom date: 6 Apr 1989
    • Machines: 520ST, 1040ST, Mega 2, Mega 4, Stacy
  • 1.06 (STE TOS, Revision 1) Support for STe machines only. Needed STE_FIX.PRG to patch bugs.
    • Format: 2 chip ROMs (256 KB)
    • Rom date: 29 Jul 1989
    • Machines: 520STE, 1040 STE
  • 1.62 (STE TOS, Revision 2) bug fixes for the previous 1.06 STE TOS.
    • Format: 2 chip ROMs (256 KB)
    • Rom date: 1 Jan 1990
    • Machines: 520STE, 1040 STE


  • 2.02 Early TOS release for Mega STE.
  • 2.05 (Mega STE TOS) Only found in the Mega STE with 720K floppy drive.
    • Format: 2 chip ROMs (256 KB)
    • Rom date: 5 Dec 1990
    • Machines: Mega STE
  • 2.06 (ST/STE TOS) Last TOS version for ST/STE computers. Bug fixes, 1.44 MB disk support, memory test. Adds GTP program support (GEM-Takes-Parameters). Greatly enhanced GEM GUI. IDE hard disk booting. Atari logo display at boot-up. Automatic cold boot memory test. Supports higher resolutions.
    • Format: 2 chip ROMs (256 KB)
    • Rom date: 14 Nov 1991
    • Machines: 520ST, 1040ST, 520STE, 1040STE
  • 2.07 used on the Falcon prototype "FX-1"
  • 2.08 used in notebook ST. ROM also contains some notebook-specific utilities: STTRANS (null-modem/ parallel-cable data transfer), power management tools, hard disk drive tools and drivers (AHDI, XHDI, BOOKINST and BOOKFMT) and a RAMdisk installer.


  • 3.01, 3.05, 3.06 (TT TOS) Primarily for 68030 TT support only. Supports fast "TT RAM", special TT screen resolutions etc. ST-hardware-compatible "Line-A" API dropped for extended TT functionality, forcing programmers to use GEM-compliant VDI calls etc. and thus encouraging GEM-compatible (as opposed to ST-compatible) development.
    • Format: 4 chip ROMs (512 KB)


TOS 4.92 (with German language selected)
  • 4.00, 4.01, 4.02, 4.04 (512 KB) Update for Falcon 030 machines only. 68030 only. Adds support for DSP, 16MHz blitter and video overlay. New v3.40 AES (last single-tasking version, but MiNT/MultiTOS-multitasking-aware) supports: pop-up menus, 3D window and dialog objects (later modified to use more compatible ob_state flags instead of extended type), 256-colour "animated" icons, soft-loaded fonts, inter-app drag&drop, background window manipulation, extensible filesystems. New CPX module for international localisation configuration. V4.04 was the last official Atari version of TOS.
  • 4.9x (4.92, 4.98) Were developed by Atari as bug-ridden internal developer version, but never officially released. Though sometimes are offered for download, the distribution is illegal.

TOS 4 ROM contains five, user-selectable language versions.

See also


  1. ^ About the meaning of TOS According to a wide-spread rumour, TOS initially meant "Tramiel Operating System" from the name of Atari Corp. President Jack Tramiel.
  2. ^ The Unofficial XaAES Page

External links


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