TOS: The Atari ST Operating System Explained
TOS (The Operating System, sometimes called Tramiel Operating System) is the operating system that powers every Atari ST, STE, TT and Falcon computer.
What TOS actually is
TOS combines a compact kernel (GEMDOS, providing file and process handling similar to CP/M and MS-DOS) with GEM (Graphical Environment Manager), the graphical desktop and windowing system that gives the Atari ST its familiar look with icons, windows and drop-down menus.
TOS vs. GEM
TOS and GEM are often mentioned together, but they're two distinct layers. TOS is the whole operating system, and it has two main parts: GEMDOS, the low-level kernel handling files, disks and processes, and GEM, the graphical environment. GEM (Graphical Environment Manager) is the desktop and windowing layer itself, providing the icons, windows and drop-down menus, plus its application programming interface. So GEM is a component of TOS, not a separate system. Its origins go back to Digital Research's GEM for the PC, which Atari adapted for the ST.
The official Atari TOS versions
The official Atari TOS versions are proprietary and were developed over the years for successive hardware generations. The most important ones:
| Version | Year | Highlights and target hardware |
|---|---|---|
| TOS 1.00 / 1.02 | 1985/86 | The original versions for the first ST models (192 KB ROM), still with many bugs and simple file handling. TOS 1.02 added Blitter and clock support. |
| TOS 1.04 | 1989 | The legendary "Rainbow TOS" with massive bug fixes, an improved file selector, real file moving on the desktop, and a faster GEM. |
| TOS 1.62 | 1991 | Adapted to the new STe hardware (sound DMA, hardware scrolling), fixing bugs of the problematic TOS 1.6. |
| TOS 2.06 | 1991 | A big step (512 KB ROM) for Mega STE/STe: built-in hard disk boot, scrolling file windows, optimised design and extended keyboard mappings. |
| TOS 3.06 | 1990 | Developed specifically for the Motorola 68030-based Atari TT030 (uses TT-RAM and higher resolutions). |
| TOS 4.04 | 1992 | The last official Atari version, for the Falcon030 with True-Color graphics modes and DSP support. |
EmuTOS: a modern replacement
EmuTOS is a modern, free, open-source replacement operating system, in contrast to the proprietary official Atari TOS versions. It's a complete reimplementation that in many ways goes beyond what the original Atari ROMs can do:
- Built-in hard disk driver, unlike the original TOS, which often needed external driver software in the AUTO folder, EmuTOS ships with universal drivers for ACSI, SCSI and IDE devices.
- Built-in command interpreter (EmuCon), the larger ROM variants include a command line for entering DOS-like text commands directly.
- Wide language and keyboard support, EmuTOS supports noticeably more languages and keyboard layouts than most regionally limited original TOS ROMs.
- Modern filesystem compatibility, optimised support for DOS-compatible FAT16 partitions, which makes data exchange with modern PCs very easy.
- Flexibility and updates, it can be run on real hardware as a ROM replacement, from floppy, or even as a program from within a running original TOS, without having to burn the physical chips.
PP's improved iTOS 1.04
The versions of TOS 1.04 modified by Pera Putnik ("PPera") add deep, unofficial system extensions that were never part of the original Atari TOS. While the original TOS 1.04 mainly fixed bugs, PPeras version breaks through the old Atari ST's hardware limits. This is the TOS I use on the "Low" machine. The main additions:
- Built-in IDE and ACSI hard disk driver (autoboot), normal TOS 1.04 can't boot directly from IDE drives or modern SD-card adapters without first loading a driver (like HDDRIVER) from floppy. PPeras version has universal hard disk drivers built directly into the TOS ROM, so the ST boots immediately and very fast from modern storage like an UltraSatan or IDE modification.
- FAT32 support and huge partitions, the original TOS 1.04 only supports the old FAT16 filesystem and is limited to small partitions (roughly 16 to 32 MB per drive). With PPeras patches, TOS 1.04 handles much larger partitions, making data exchange with modern PCs via SD card very easy.
- "Chimera" versions (TOS 1.04 with the TOS 2.06 desktop), these combine the stable, highly compatible core of TOS 1.04 with the more modern desktop of TOS 2.06. You get the comfort of TOS 2.06 (better file windows, desktop shortcuts) while keeping the near-100% game compatibility of the old TOS 1.04.
- RAM optimisation for games (Raw Image Access / RIA), special code in the ROM can stream games directly from hard disk or SD card as an image, so even large 1 MB games run on machines that would otherwise have too little memory for hard disk loaders.
KAOS TOS
KAOS TOS is a comprehensive software patch for the Atari ST's TOS, developed from 1990 to fix bugs and boost performance. It's not a standalone operating system but a patch for the original Atari TOS, mainly based on TOS 1.02 and TOS 1.04. The developers corrected over 80 known programming errors in the original system. KAOS 1.2 was published in the c't magazine, while the later KAOS 1.4.2 was sold commercially.
It ran noticeably faster, and although critics claimed this was only from disabling visual effects, re-enabling them disproved that. Since the Atari ST keeps its operating system in ROM, KAOS was often burned onto EPROM chips and physically installed in the machine. Most cleanly written applications ran without problems, with special helper patches for the few incompatible ones. Atari never officially licensed the project but tolerated it on the market. It was shaped by Andreas Kromke and Normen Kowalewski, among others, and became well known in the Atari community through coverage in the ST-Magazin.
KAOS TOS is also installed on my "Low" machine, though I rarely use it. Theoretically it's there and available if needed.
Adding multitasking: Geneva and MiNT
Plain Atari TOS is a single-tasking system: only one main program runs at a time. Two well-known add-ons change that.
Geneva
Geneva is a resource-friendly, self-contained multitasking environment for the Atari ST. It runs on top of normal TOS and replaces or extends GEM, letting several GEM programs and accessories run in parallel, even on older and weaker Atari models without a big performance hit. It needs little memory and stays very compatible with older software that was never written for multitasking, which is why I run it on the "High" workstation.
MiNT
MiNT (originally "MiNT is Not TOS", later "MiNT is Now TOS") is a much more powerful, Unix-like replacement kernel. It swaps GEMDOS for a Unix-style memory and process management layer, and together with a graphical shell like XaAES or N.AES it enables true, modern multitasking, today usually known as FreeMiNT. The catch is that it often needs stronger hardware, ideally a processor with a memory-management unit (PMMU) such as the Motorola 68030 in the TT or Falcon, and tends to run slowly on a bare old ST. I haven't managed to get MiNT running reliably on any of my machines, which is exactly why the "High" machine uses Geneva instead.