Atari ST

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Atari 520ST.

The Atari ST was the first TOS machine developed by Atari Corporation, being released in 1985. For the time, the ST featured a powerful processor, a large amount of memory, a colourful display, and an easy-to-use GUI operating system, all for a very cheap price. These attributes all contributed to ST representing a significant evolution in the personal computer market, and consequently it was a massive commercial success. Without this success, the TOS Family would not have existed.

The name ‘ST’ is derived from the capabilities of the Motorola 68000 processor upon which the original Atari line was based. The 68000 uses a Sixteen-bit data bus with a Thirty-two bit address bus.


The original ST computers featured the following:

  • Motorola 68000 32-bit Central Processor Unit (CPU) running at 8MHz.
  • Integrated GEM / TOS operating system.
  • RAM memory storage of 256k, 512k, or 1 Mbyte.
512KB in the first signifcant base model, the 520 (early 260 models existed with only 256KB of memory). The 1040ST was equipped with 1MB of RAM.
  • Built-in MIDI, dual joystick, floppy drive, ACSI, serial, and parallel ports.
  • Sophisticated DMA peripheral access.
  • Yamaha 3-voice FM sound generator.
  • External 128k cartridge port.
  • Integrated video controller capable of generating (320x200x16), (640x200x4), and (640x400x2) ST Video Modes from as many as 512 colors.



The original ST released in June 1985, initially only as a 520ST with 512kb of RAM, an external floppy disk, and external power supply


As original ST, but with factory fitted 1MB 'piggyback' upgrade


The M signifying the built in RF modulator for output to television sets. The STM was the last small form factor ST - all subsequent ST's had built in power supplies.


The F signifies a built in floppy drive, as well as internal power supply and floppy drive


Floppy, Modulator

Mega ST

First released in 1986, the Mega ST was aimed more at the professional and business market. Originally called the "ST1", the Mega ST featured a blitter and had a more traditional PC form factor than the ST, with the motherboard in a desktop case with separate keyboard. Initially released in 2mb and 4mb models only, a 1mb model was later released, the Mega 1


The E signifying "enhanced", seen by many as an attempt by Atari to close the gap to the Amiga OCS chipset. The STE had a number of enhancements to the chipset, including:

  • A palette increase from 512 to 4096 colours
  • A blitter chip, previously only included in the Mega ST
  • DMA and other additions to the glue chip
  • Hardware scrolling
  • Stereo PCM sound output, with steroy RCA outputs
  • Analog joystick ports on the left side of the case
  • SIMM slots for easy memory expansion to 4MB

Mega STE

The Mega STE had more significant differences over the STE, compared to the Mega ST over the standard ST. As well as being in a desktop case with a separate keyboard, it featured:

  • 68000 switchable from 8mhz to 16mhz in software, with 16kb of cache
  • A socket for a 68881 or 68882 FPU
  • Internal SCSI hard drive (connected with ACSI -> SCSI adapter board)
  • 1.44MB floppy drive in later revisions
  • VME expansion slot
  • Apple Talk network port
  • TOS 2


  • It was a success, explain why - price, power. Influence, competition with Amiga


  • Discuss development politics, Sam Tramiel leaving Atari, all that stuff