Atari ST

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The Atari 520 ST

The Atari ST was a home/personal computer system released by Atari in 1985. The "ST" allegedly stood for "Sixteen/Thirty-two" which referred to the Motorola 68000's 32-bit internals with 16-bit external buses. Other theories say that ST really stood for "Sam Tramiel", the son of Atari owner Jack Tramiel. This is a plausible explanation, since the Atari ST also used a bumblebee as the busy mouse pointer image, which might be a reference to Jack's birth name.



The Atari ST was a notable home computer, based on the Motorola 68000 CPU, with 512KB of RAM or more, and 3.5" floppy disks as storage. It was similar to other contemporary machines which used the Motorola 68000, the Apple Macintosh and the Commodore Amiga. Although the Macintosh was the first widely available computer with a graphical user interface (GUI), it was however limited to a monochromatic display. The Atari ST was notable, being the first computer with a fully bit-mapped color GUI. It had an innovative single-chip graphics subsystem (designed by Shiraz Shivji) which shared the full amount of system memory, in alternating clock cycles, with the processor, similar to the earlier BBC Micro and the Unified Memory systems that have become common today. It was also the first home computer with integral MIDI sound support.

The ST was primarily a competitor to the Commodore Amiga systems. This platform rivalry was often reflected by the owners and was most prominent in the Demo Scene. Where the Amiga had custom hardware which gave it the edge in the games and videowork market, the ST was generally cheaper and slightly faster at basic operation. Thanks to its built-in MIDI ports it enjoyed success as a music sequencer and controller of musical instruments among amateurs and professionals alike, being used in concert by bands such as Tangerine Dream. In some markets, particularly Germany, the machine gained a strong foothold as a small business machine for CAD and Desktop publishing work.

The ST was later superseded by the Atari TT and Falcon computers, and ST technology was used in the creation of the Atari Jaguar video game console.

Since Atari pulled out of the computer market there has been a market for powerful TOS-based machines (clones). Like most "retro" computers the Atari enjoys support in the emulator scene.


Atari had created two released machines in the form of the Atari 2600 console (also known as VCS) and the various Atari 8-bit based home computers. Both of these lines were created around the 6502 CPU and included a number of additional chips assisting this rather basic, but cost-effective CPU in providing graphics and sound. In fact the 8-bit machines had originally intended to be the replacement for the 2600, but they were later "re-purposed" as home computers to cash in on that market segment's much higher selling prices.

As Atari grew and the management was shuffled by Warner (their parent company), the creators of the 2600 and 8-bit machines eventually got fed up and left. A group of them led by Jay Miner formed a small think tank called Amiga in 1982 and set about creating the third generation machine, this time based on the much more powerful 68000 CPU.

During this time, the home computer market started to slow down, and the video game market underwent the great video game crash of 1983. Warner management decided to "get out" and started looking to sell Atari outright. Meanwhile many of the same effects were in the process of decimating Commodore International. An argument involving Commodore's chairman Irving Gould, and Jack Tramiel ensued, resulting in Tramiel's immediate departure from Commodore in January of 1984.

Tramiel immediately formed a holding company, Tramiel Technology, and brought in a number of ex-Commodore staff to start a rush project to develop a new, high-performance home computer. While this team, led by Shiraz Shivji, worked on the design, Tramiel started making overtures to buy Atari from Warner. The design team considered "one-upping" the Macintosh by using a full 32-bit chip, namely the NS32032, but in talks National Semiconductor couldn't supply the numbers of price the project needed. In retrospect this proved to be lucky, a prototype built on the NS32032 proved to be slower than the 16-bit 68000.

The basic hardware design quickly "gelled" into a form that was almost identical to the ST that eventually shipped. The design used off-the-shelf parts where possible. Disk drive support was provided by the WD1770, a standard Western Digital chip, and sound from a Yamaha YM2149, a clone of the common but fairly basic General Instruments AY-3-8910. Serial, MIDI, and other I/O functions were provided by standard Motorola chips. The custom chips included a memory controller, the simple "Shifter" graphics chip, a DMA controller, and the "GLUE" interrupt handler.

At about the same time, Amiga were desperate for a buyer or investor, and the "Warner owned" Atari had paid Amiga for development work (see: "TOP SECRET: Confidential Atari-Amiga Agreement" ( In return Atari was to get one-year exclusive use of the design. By May Tramiel had secured his funding, bought the remains of Atari from Warner for a very low price, and set about re-creating his empire.

When Tramiel took over the company he tried to leverage this and take ownership of the Amiga properties. Right under the noses of Atari, and at the 11th hour for Amiga, Commodore purchased Amiga lock, stock, and barrel. Tramiel was furious, and the resulting court case lasted for years. In the meantime this left Atari with an incomplete 16-bit design, while Commodore would soon have the best.

Work thus continued with the design started at Tramiel Technology. With the basic design complete, the team started looking at solutions for the operating system. Soon after the buyout Microsoft approached Tramiel with the suggestion that they port Windows to the platform, but the delivery date was out about two years, far too long for their needs. Another possibility was Digital Research, who were working on a new GUI-based system then known as Crystal, soon to become GEM. A final possibility was to write a new system in-house, but this was eventually rejected due to risk.

DR seemed generally uninterested in porting the system themselves, so a team from Atari was sent to their Monterey headquarters to do it themselves. They were given the latest versions of the Intel 8086 code from their DR counterparts, and would port it to the 68000 as quickly as possible. A version, running on top of CP/M-68K, was available just in time for the January 1985 CES, where the ST was introduced.

TOS 1.0 with the GEM user interface
CP/M-68K was essentially a direct port of CP/M's original, and very old, operating system. By 'modern' standards of 1985, it was rather outdated both in terms of command structure, and that it didn't support hierarchical file systems. DR was also in the process of building a new DOS-like operating system specifically for GEM, GEMDOS, and there was some discussion of whether or not a port of GEMDOS could be complete in time for product delivery in June. The decision was eventually taken to port it, resulting in a GEM/GEMDOS system Atari referred to as TOS. This was beneficial to the system, as it allowed the ST to read and write standard IBM PC disks.

The design shipped in June 1985 as the 520ST. The machine had gone from concept to store shelves in a little under a year. Atari had originally intended to release versions with 128 KB and 256 KB of RAM as the 130ST and 260ST respectively, but the rapidly falling prices of RAM at the time led them to cancel these versions and it was released with 512K only. In 1986 the 1040STF shipped with 1MB of RAM and featured an integral PSU and double sided floppy-disk drive. However the ST remained generally the same internally over the majority of its several-year lifespan. The choice of model numbers was inherited from the model-numbers of the XE series of the Atari 8-bit family of computers.


The 520ST was an all-in-one unit, similar to earlier home computers like the Commodore 64. However by this time the market demanded a "full sized" keyboard, including cursor keys and a numeric keypad. For this reason the 520ST was fairly "boxy", generally oversized for a machine that one had to move around to adjust the keyboard position. Adding to this problem was the number of large cables needed to connect to the peripherals. This problem was addressed to some degree in the follow-on models which included a built-in floppy disk.

Following most machines of the era, and thus differing greatly from earlier Atari designs, the ST used a large number of one-off ports mounted on the rear of the machine. In addition to power and monitor connections, the ST included an RS-232 serial port, a Centronics printer connection, two Atari-standard joystick/mouse ports, a hard drive connector (not SCSI), the floppy disk connector, a cartridge port and the two MIDI ports.

The case followed the Tramiel-Atari design of the era, being basically wedge shaped, with a series of grilles cut into the rear for airflow. Atari machines under the Tramiel rule are marked by infamously "cheap" cases. The original 520 design was quite flimsy, and while the 1040 ST-style case was much stronger, it was also becoming too large and rather unwieldy. In addition the majority of the machines had very poor quality keyboards, so poor that there was a burgeoning third-party market for spring kits to improve the feel. They got the design completely right with the Mega ST series which included a detached high-quality keyboard and stronger case, but this apparently cost too much to produce and the design was not used widely.

An annoying problem concerned the disk drives. Early models were shipped with an external single-sided drive that could store up to 360KB, with an optional double-sided version that stored 720KB for considerably more money. Due to the early sales of so many of the single-sided drives, almost all software would ship on two single-sided disks instead of a single double-sided one, in fear of cutting off all the other owners. This was true even years later, long after the single-sided drives had been taken off the market.

Additionally they had originally intended to include GEM's GDOS hardware abstraction layer, which allowed programs to draw (display, print, etc.) graphics to any supported device with no changes. This allowed developers to write a program for display to the screen, and get high quality printing "for free". However GDOS was not ready at the time the ST started shipping, and while Atari promised to include it as soon as possible, they never did. This left printing support up to the developers, who had to create their own engines for every possible printer.

Similarly the custom "BLiTTER" was to be included to speed the performance of graphics operations on the screen, but this was isolated to their "upscale" machines when it was eventually released years later. As a result, the power of GEM was largely lost on the ST platform, even when GDOS and BLiTTER eventually shipped, it was ignored by developers because it was on so few machines.

On the plus side the ST was less expensive than most machines, including Macintosh Plus, and tended to be faster than most (external link: price comparison ( Largely as a result of the price/performance factor, the ST would go on to be a fairly big seller, notably in markets where the foreign exchange rates amplified prices. For this reason the ST was most popular in Europe, especially in Germany. Also, the very crisp, 640 by 400 pixels picture of its black & white monitor made it popular for small-office applications. In fact, an Atari ST and reasonable terminal emulation software was much cheaper than a Digital VT220 terminal that was normally needed by offices with central computers.

The super STs

For about the first four years, nothing much had changed in the capabilities of the ST platform, except for new machines being released with greater RAM. In late 1989, Atari released the STE — a version of the ST with some improved hardware. Among the new features were 4096 colours to choose from instead of 512, a new digital sound-chip that could play stereo samples in hardware (the Yamaha YM2149 could only be coaxed into playng samples by means of software) and a BLiTTER. Two analogue joystick-ports were added (two normal joystics could be plugged into each port with an adaptor). Despite all this, it still ran at 8MHz.

The STE models initially had serious operating systems conflicts resulting in many applications and games written for the ST line being unusable (sometimes, this could be solved by expanding the RAM). To make matters worse, the built in floppy disk drives could not read as many tracks on a floppy disk as the built in floppy disk drives on older models. While this was not a problem for most users, some games used the extra tracks as a crude form of copy protection (and as a means of cramming more data on the disk). Furthermore, having a joystick plugged in would sometimes cause strange behaviour with a few apps (such as First Word Plus).

Not much use was made of the extra features of the STE, and STE-enhanced and STE-only software was rare. Look in external links for Atari STe fanpage, there you will find what software use special Atari STe abilities.

Atari went on to release the Mega STE (an STE in a Mega-ST case that ran at 16MHz).

At some time during the early '90s, the development of the ST line forked. On one branch was the high-end workstation-oriented TT, and on the other was the entertainment-oriented Falcon — all which were supposed to be ST compatible, but not compatible with eachother. By then, the ATARI ST platform was dying and neither of these two machines took off.

Medusa Computer Systems manufactured some 3rd-party Atari Falcon/TT-compatible machines that used 68040 and 68060 processors.

Future of the Platform

Despite the lack of a hardware supplier and commercial software vendors, there is a small active community dedicated to keeping the ST platform alive. There have been advancements in the operating system, software emulators (For Windows, Mac & Linux), and some hardware developments. There are accelerator cards, such as the CT-60, which is an 68060 based accelerater card for the Falcon, and there is the Atari Coldfire Project, which aims at developing an Atari-clone based on the Coldfire processor.


As the ST was the first home computer with built in MIDI ports, there was plenty of MIDI-related software. Also popular on the ST was Desktop publishing software.

The ST came bundled with a disk that contained amongst other things ST BASIC, the first BASIC for the ST. However, due to it's poor quality, it was eventually replaced by other BASICs.

There was a thriving output of public domain and shareware software which was distributed by public domain software libraries.

The ST was one of the leading platforms for games in the late 1980s, but in the early 1990s, the software houses gradually stopped producing ST versions of the games. See List of Atari ST games and Category:Atari ST games.



Screenshot of GEM (Desktop) Missing image
Screenshot of Neochrome

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Screenshot of 1st Word

Screenshot of STZip
GEM (Desktop) Neochrome 1st Word STZip
Atari/Digital Research (1985) Dave Staugas (1985) GST (1985) Vincent Pomey (1994)
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Screenshot of Dungeon Master

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Screenshot of MIDI Maze

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Screenshot of Populous

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Screenshot of Xenon 2

Dungeon Master MIDI Maze Populous Xenon 2
Mirrorsoft/FTL (1987) Hybrid Arts (1987) EA/Bullfrog (1989) Bitmap Brothers (1989)

More screenshots can be found on the Atari ST Games page.

Technical specifications


As originally released in the 520 ST:

Very early machines included the OS on a floppy disk, but this was quickly replaced with ROM versions of TOS 1.0 instead. The later models also used an upgraded version of TOS - 1.02 (also known as TOS 1.2). Another early addition (after about 6 months) was an RF Modulator that allowed the machine to be hooked to a colour TV when run in its low resolution mode. These models were known as the 520STm. Later f and fm models of the 520 had a built in double-sided disk drive instead of a single sided one.


As originally released in the 520 STe:

  • All of the features of the 520ST
  • Drive: built-in double-sided 3½" floppy disk drive
  • Built in RF Modulator
  • Extended palette of available colours to chose from — 4096.
  • BLiTTER chip.
  • Hardware-support for horizontal and vertical fine scrolling.
  • 2 Channel Stereo 8-bit PCM sound.
  • 30-Pin SIMM memory slots to upgrade memory up to 4Mb.
  • Ability to synchronise the video-timings with an external device so that a video Genlock device can be used without having to make any modifications to computer's hardware.
  • Additional ports: Stereo RCA jacks and two analogue joystick ports (with support for analogue devices such as paddles and light pens. Two normal digital joysticks could be plugged into each analogue port with an adaptor).
  • TOS 1.06 (also known as TOS 1.6) on ROM.

Later STe models had TOS 1.62 that fixed some bugs in TOS 1.6


A number of machines were released in the ST family. Here they are, in rough chronological order after the original 520 ST:

  • 520 ST+ - Name for early 520 STs with 1 MB of RAM, but without floppy disk
  • 260 ST - European name for the 520 ST with 512 KB. Used after the release of the 520 ST+ to differentiate the cheaper 512 KB models from the 1 MB models
  • 520 STm - a 520 ST with a built-in modulator for TV output.
  • 520 STfm - a 520 STm with a newly redesigned motherboard in a larger case with a built-in floppy disk drive
  • 1040 STf - a 520 STfm with 1 MB of RAM and a built-in double-sided floppy disk, but without modulator
  • 1040 STfm - a 520 STfm with 1 MB of RAM and a built-in double-sided floppy disk
  • Mega ST (MEGA2, MEGA4) - 1040 with 2 or 4MB of RAM, respectively, in a much improved "pizza box" case with a detached keyboard. These models included the BLiTTER chip, but the OS ROM was not upgraded and the extra GEM functionality needed to be booted from disk.
  • 520 STe and 1040 STe - enhanced sound, the BLiTTER chip, and a 4096 color palette, in the older 1040 style all-in-one case
  • Mega STE - same hardware as 1040 STe except for a faster 16 MHz processor, in the TT case
  • STacy - A portable (but definitely not laptop) version of the ST. Originally designed to operate on 12 standard C cell flashlight batteries for portability, when Atari finally realized how quickly the machine would use up a set of batteries (the batteries were not rechargeable), they simply glued the lid of the battery compartment shut.
  • ST Book (later version portable ST)

Other models

  • Atari TT030 — new machine based on the Motorola 68030 processor running at 32 Mhz, in yet another new case design with a detached keyboard.
  • Atari Falcon 030 — another '030 based machine like the TT, but in the 1040 style case (yet again) with another upgrade to the graphics, sound, a Motorola 56000 DSP, multitasking OS (on disk) and a LocalTalk port for networking
  • Medusa 040, Medusa 060, Hades 040, Hades 060 — 3rd-party Falcon/TT compatible machines manufactured by Medusa Computer Systems.
  • Atari ABAQ, or Atari Transputer Workstation — A standalone machine containing ST hardware and up to 17 transputers capable of massively parallel operations for tasks such as ray tracing.

There were also some unreleased prototypes: Falcon 040 ( (external link) (based on a Motorola 68040, new case and slots), and STylus (palmtop)

See also

External links



The machines

  • Atari Gallery ( – Descriptions of the various ST models; courtesy of YesCREW (

Free Emulators

(there are also commercial emulators)


3rd-party manufacturers

  • Medusa Computer Systems ( — Manufacturers of the Medusa 040, Medusa 060, Hades 040, Hades 060.

Lists of links

fi:Atari ST fr:Atari ST it:Atari ST sv:Atari ST


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