Operating systems
for Atari computers

The TOS is the native Atari operating system, which comes together with each Atari computer. The first version, 1.0, also known as RAM TOS was loaded from disk, each next version is burned into system ROM at the factory.

Each TOS version Atari has developed, apart from the official number, is also known under an unofficial name:

• TOS 1.0 - RAM TOS, since it was loaded from disk and resided in the system RAM.
• TOS 1.02 - Blitter TOS was introduced with the Mega ST computer and contained routines supporting the Blitter, a graphic co-processor.
• TOS 1.04 - Rainbow TOS, since it displays a rainbow Atari logo in the info box.
• TOS 1.62 - STE TOS was introduced with STE computer series.
• TOS 2.0x - Mega TOS was developed for Mega STE computer.
• TOS 3.0x - TT TOS was developed for the Atari TT030.
• TOS 4.0x - Falcon TOS also known as 3D TOS is present in the Falcon030 computer and provides 3D-looking window elements.
• TOS 5.0 - the real Falcon030 TOS was supposed to become the native system of Falcon computers, but has never been officially released. The only available version is a beta release known as TOS 4.92.

System structure

The TOS consists of four main parts, each one can be replaced by a RAM-based substitute:

• BIOS, Basic Input/Output System, provides several hardware dependent functions and is basically compatible with PC BIOS. Additionally, the ST-BIOS contains an enhancement, known as XBIOS (Extended BIOS). The XBIOS functions are strictly platform dependent and aren't compatible with any other computer, but ST.
• GEMDOS, is the main file management subsystem. The GEMDOS has been developed by the Digital Research, Inc. and is compatible with DR-DOS. The GEMDOS may be replaced with MiNT kernel in order to use MiNT networking software.
• VDI, Virtual Device Interface, is a library of hardware dependent graphic functions. Generally, it is responsible for drawing basic screen elements (points, lines, filled and empty objects, fill textures, fonts etc.) and controlling the mouse. The VDI has also an optional, loadable extension called GDOS, mainly responsible for font management. Latest GDOS versions support Bitstream and True Type character sets. The VDI may be replaced with NVDI, which is much faster and provides some additional functions.
• AES, Application Environment Manager, is a fully hardware independent window and application manager. The AES and the VDI, both developed by the Digital Research, Inc., are known as GEM, Graphic Environment Manager. The standard AES (version 3.40 in Falcon TOS) may be replaced with the MultiAES (AES 4.10), a part of MultiTOS 1.08 or with the Geneva, which converts the TOS to a co-operative multitasking system.

Besides of that, the system ROM contains also the GEM Desktop, i.e. an application program directly responsible for user interaction with the TOS.
This structure, in order to keep compatibility with the TOS, is present in some other operating systems.

Short characteristic

The main advantage of the TOS is that it is fast, stable and not memory hungry - if you don't load many TSRs, it gives you about 3,7 MB of TPA on a 4 MB machine, since it doesn't utilize the system RAM to keep it's own code into. But even considering that the system resides in ROM, you must prove that the TOS code is generally compact: the latest version, Falcon TOS, fits in a 512k chip together with the desktop and five resource files for five different nationalities. Also notice, that the TOS will work fine even if there is no hard drive connected - you can run the system from a floppy and have a serious chance, that all necessary system files won't take more than 1% of the capacity on a standard 1,44M diskette.

The main disadvantage of the TOS is that it doesn't support true multitasking: only one application can be used at once together with up to six so called accessories, which have to be loaded at startup and must be present in the memory all the time the system is running. The accessories may run in parallel with the main application using some sort of cooperative multitasking - the system switches the CPU time between those seven tasks if they interact with the GEM. If the application or one of the accessories executes an operation which runs without any system call, task switching is impossible and the rest is stopped.

Additionally, the TOS doesn't support big logical drives. You can have up to 16 logical drives, 14 of them can be hard disk partitions. Each one is limited to 32766 data clusters, up to 16384 bytes each. It means, that the maximum capacity of a partition is about 512 MB.

Summa summarum, the TOS cannot be currently considered as a modern operating system, but one has to remember that the latest version of the system has been released four years ago. That time big hard drives were rather rarely used in home computers and only one of popular operating systems supported true pre-emptive multitasking, namely the AmigaOS. Now the TOS is a bit out of date and has few devotees in the Atari community. Majority has moved to systems mentioned below.

The MultiTOS has been developed by Atari Corp. to be a TOS replacement for those who would like to have a true multitasking system. Unlike the TOS, the MultiTOS is a fully RAM-based system and in fact consist of the MiNT kernel (that is described in one of the further sections) and a new, multitasking version of the AES (MultiAES). Due to this reason, the MultiTOS can theoretically support all of the MiNT possibilities, since in fact it is nothing else than the MiNT configured to be TOS and GEM compatible.

The MultiTOS provides the true, pre-emptive multitasking and supports many additional functions which are needed in such a system, e.g. memory protection, multiple filesystems, startup sequence scripts, standardized system enhacements, easy task selection, window iconification, loadable accessories, unlimited number of concurrent applications and many more. Additionally, it is much more configurable than the TOS and follows the general trend in programming of a modern operating system.

Unfortunately, bad financial condition in 1993. has enforced the Atari Corp. to drop all ST-line support. MultiTOS was one of the victims of that decision. The latest official version, 1.04, was not perfect and has been quickly forgotten by the Atari community. Interestingly, the latest unofficial beta, MultiTOS 1.08, was way better and has began a general guideline for programmers developing software and replacement operating systems. In fact, the MultiTOS 1.08, never officially released, never officially supported and used only by a few heroical devotees - has become a standard.

The MagiC has been introduced to the market about two years ago by a German company called Application Systems Heidelberg, previously known as the developer of a C compiler (Pure C) and has become popular very quickly, breaking the Atari community into Magic's devotees and enemies.

The MagiC is a modern operating system without any doubt. It is probably also the only and unique complete TOS replacement, which doesn't use any of the TOS components. It follows the main MultiTOS guidelines (though some of the MultiAES, or even Falcon AES, functions are missing) and, furthermore, tries to enforce a new standard for software developers by supporting many of Digital Research GEM/2 functions (which are missing in the Atari GEM) as well as several own enhancements.

Besides of the multitasking (both pre-emptive or co-operative, depending on a user selection), the MagiC supports a new filesystem in order to allow you to use long filenames and really big disks, easy task management, background DMA transfers, fast GEMDOS, fast AES, fast VDI and many more features. Additionally, although it is a RAM-based system, it is compact and not memory hungry - the whole system takes less than 300 kilobytes. Furthermore, it opens a way for the Atari community a way to use GEM applications with newer hardware - since there's no hope to see new products of the Atari Corp. as the company is dead, the Application Systems Heidelberg released the MagiC versions for Apple computers and PCs. They are claimed to be GEM compatible and are supposed to allow you to use GEM applications on these platforms.

The MiNT is a system originally based on the BSD package ported to ST computers by Eric R. Smith. It was supposed to be a backdoor for the Atari community to the Unix world with loads of BSD based network applications. A short (1992-94) romance of the MiNT and Atari Corp., which decided to convert the system to the MultiTOS kernel, has caused a birth of an unique TOS/Unix hybrid, which gives you simultaneous access to both GEM and BSD application libraries.

Since the MiNT is the MultiTOS's kernel, it has kept all the features described above and, if an AES replacement is installed, it can show you a new face of the MultiTOS. Unlike the MultiTOS however, the Unix-like MiNT is based on a different filesystem, which is much faster and more flexible than the TOS FS. Furthermore, thanks to the excellent network support, the MiNT gives you an unique possibility to convert your Atari to a true Internet server, which will still be able to run GEM and TOS applications! Thanks to this feature, the MiNT has a lot of devotees in the Atari community(they're recently considered as MiNTquisitors) and is the main competitor for ASH's MagiC.

Unlike the Linux, the MiNT contents itself with Motorola 68000 without an FPU, but similarly to other Unix systems it requires much more memory to work in a decent setup. A 4 MB is an absolute minimum, if you want to have a multiuser configuration however, and to run GEM applications at the same time, it will require at least 8 MB or more.

To be continued...

Operating system summaries

System component replacements