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The Atari 520ST and various models. . .

The Atari 520st was officially launched to us by the Atari Corporation in January 1985 at the Winter Consumer Electronics Show in Las Vegas.  The letters “ST” stands for “Sixteen/Thirty-two”, which refers to the Motorola 68000’s 16-bit external bus and 32-bit internals.

Other machines that arrived at a similar time were the Apple Macintosh and the main contender being the Commodore Amiga.  Although the Amiga had custom processors which gave it the edge in the games and video market, the Atari ST was generally cheaper, had a slightly faster CPU, and had a high-resolution monochrome display mode, ideal for business and CAD.

The Atari ST was also to be the first home computer to feature integrated MIDI support.  Thanks to this unique feature the system enjoyed great success for running music-sequencer software and also more importantly as a controller of musical instruments among amateurs and professionals alike.

The members of the ST family are listed below, in rough chronological order:

original model with 512 kB RAM.
intended to be a 128 kB variant. Announced at the 1985 CES alongside the 520ST but never produced.
early 520STs with 1 MB of RAM, but without floppy disk
originally intended to be a 256 kB variant, but actually sold in small quantities in Europe with 512 KB. Used after the release of the 520ST+ to differentiate the cheaper 512 KB models from the 1 MB models
a 520ST with a built-in modulator for TV output.

a 520STM with a newly redesigned motherboard in a larger case with a built-in disk drive.

a 520STFM with 1 MB of RAM and a built-in double-sided floppy disk, but without RF modulator.
a 520STFM with 1 MB of RAM and a built-in double-sided floppy disk with RF modulator.
Mega ST (MEGA2, MEGA4)
had a redesigned motherboard with 2 or 4 MB of RAM, respectively, in a much improved “pizza box” case with a detached keyboard.  Early models did not include the BLiTTER chip; most did.  Also included was a real-time clock and a internal expansion connector.
520STE and 1040STE
a 520STFM/1040STFM with enhanced sound, the BLiTTER chip, and a 4096-color palette, in the older 1040 style all-in-one case.
as 1040STE but with 4 MB of RAM.  This machine was never officially released except a small quantity of development units.  Labels were sent out to dealers so they could affix them to the machines that had been upgraded to 4MB.
Mega STE
same hardware as 1040STE except for a faster 16 MHz processor, an onboard SCSI controller, additional faster RS232 port, VME expansion port, in the TT case
was a portable version of the ST.  Originally designed to operate on 12 batteries for portability, when Atari finally realized how quickly the machine would use up a set of batteries (especially when rechargeable batteries of the time supplied insufficient power compared to the intended alkalines), they simply glued the lid of the battery compartment shut, and funnily enough, this machine was soon discontinued.
was a later version of the portable ST, more portable than the STacy machine, but sacrificing several features in order to achieve this — notably the backlight, and internal floppy disk mainly to save power.  Files were meant to be stored on a small amount (one megabyte) of internal flash memory ‘on the road’ (as it was known) and transferred using serial or parallel links, memory flashcards or external (and externally powered) floppy disk to a desktop ST once back indoors.  The screen is highly reflective for the time, but still hard to use indoors or in low light, it is fixed to the 640×400 1-bit mono mode, and no external video port was provided.  For its limitations, it gained some popularity, particularly amongst musicians of the era.
Here’s a nice little line-up of games that I remember vey well.


As originally released in the 520ST:

  • CPU: Motorola 68000 16-/32-Bit CPU @ 8 MHz. 16 bit data/32 bit internal/24-bit address.
  • RAM: 512 KB or 1 Megabyte
  • Display modes (60 Hz NTSC, 50 Hz PAL, 71.2 Hz monochrome):
    • Low resolution – 320×200 (16 color), palette of 512 colors
    • Medium resolution – 640×200 (4 color), palette of 512 colors
    • High resolution – 640×400 (mono), monochrome
  • Sound: Yamaha YM2149 3-voice squarewave plus 1-voice white noise mono Programmable SoundGenerator
  • Drive: Single-sided 3½” floppy disk drive, 360 KB capacity when formatted to standard 9 sector, 80 track layout.
  • Ports: TV out (on ST-M and ST-FM models, NTSC or PAL standard RF modulated), MIDI in/out (with ‘out-thru’), RS-232 serial, Centronics parallel (printer), monitor (RGB or Composite Video colour and mono, 13-pin DIN), extra disk drive port (15-pin DIN), DMA port (ACSI port, Atari Computer System Interface) for hard disks and Atari Laser Printer (sharing RAM with computer system), joystick and mouse ports (9-pin MSX standard)
  • Operating System: TOS v1.00 (The Operating System) with the Graphical Environment Manager (GEM) WIMP (Windows, Icons, Menus, Pointer) GUI

Very early machines included the OS on a floppy disk due to it not being ready to be burned to ROM (Like the Amiga 1000 had).  This early version of TOS was bootstrapped from a very small core boot ROM, but this was quickly replaced with (expanded capacity) ROM versions of TOS 1.0 when it was ready.  (This change was also greatly welcomed as older ST machines with memory below 512 KB suffered, as GEM loaded its entire 192 KB code into RAM when booting the desktop).

Having the OS loaded from disk was due to Atari trying to rush the machines to market without ironing out all the bugs in the OS.  Soon after this change, most production models became STFs, with an integrated single- (520STF/512 KB RAM) or double-sided (1040STF/1024 KB RAM) double density floppy disk drive built-in, but no other changes.  The next later models 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 or medium resolution (525/625 line 60/50 Hz interlace, even on RGB monitors) modes, greatly enhancing the machine’s saleability and perceived value and saving the cost of having to purchase a monitor for the system.  These models were known as the 520STM (or 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 520STE/1040STE:

  • All of the features of the 520STFM/1040STFM
  • Extended palette of 4,096 available colours to choose from
  • BLiTTER chip for copy/fill/clear large data blocks in memory (fill rate 4 MB/s)
  • Hardware-support for horizontal and vertical fine scrolling and split screen (using the Shifter video chip)
  • DMA sound chip with 2-channels stereo 8-bit PCM sound at 6.25/12.5/25/50 kHz and stereo RCA audio-out jacks (using enhancements to the Shifter video chip to support audio shifting)
  • National LMC 1992 audio controller chip, allowing adjustable left/right/master volume and bass and treble EQ via a “Microwire” (3-bit serial) interface
  • Memory: 30-pin SIMM memory slots (SIPP packages in earliest versions) allowing upgrades up to 4 MB Allowable memory sizes including only 0.5, 1.0, 2.0, 2.5 and 4.0 MB due to configuration restraints (however, 2.5 MB is not officially supported and has compatibility problems). Later 3rd-party upgrade kits allow a maximum of 14MB w/Magnum-ST, bypassing the stock MMU with a replacement unit and the additional chips on a separate board fitting over it.
  • 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
  • Analogue joypad ports (2), with support for devices such as paddles and light pens in addition to joysticks/joypads.  The Atari Jaguar joypads and Power Pad joypads (gray version of Jaguar joypads marketed for the STE and Falcon) can be used without an adapter.  Two standard Atari-style digital joysticks could be plugged into each analogue port with an adapter.
  • TOS 1.06 (also known as TOS 1.6) or TOS 1.62 (which fixed some major backwards-compatibility bugs in TOS 1.6) in two socketed 128 KB ROM chips.
  • Socketed PLCC 68000 CPU

Port connections

The ST featured a large number of ports mounted at the rear of the machine.

  • Standard ports:
    • RS-232c serial port (DB25 male)
    • Centronics printer port (DB25 female)
    • joystick/mouse ports (DE-9 male)
    • 2 MIDI ports (5-pin DIN)
  • ST-specific ports:
    • Monitor port (13-pin DIN)
    • ACSI (similar to SCSI) DMA port (for hard disks and laser printers)
    • Floppy port
    • ST cartridge port (for 128 KB ROM cartridges)

Here is a short atari st commercial for the early eighties featuring Alan Alda (Alphonso Joseph D’Abruzzo) from the tv programme MASH.

I never really got to grips properly with the Atari ST because although i had heard of it, it had somehow passed me by.  Truthfully,  i think it was probably because i was an avid Amiga user and surrounded by hardcore Amiga enthusiasts lol.  Similar to my Sinclair Spectrum experience, once again i purchased a nice boxed version to add to my collection but this time, after using the Atari ST and getting to know it a little better i found that there really wasn’t much difference between the Atari ST and the more expensive and as popular Commodore Amiga.

I firmly believe because of the Atari STs low cost, built-in MIDI ports, and fast, low-latency response times this made it a fantastic piece of Hardware for musicians to play around with.  The following supporting facts really speak for themselves:

  • Atari Teenage Riot named itself after the brand and programmed most of their music on an Atari ST. Including the entire album Is This Hyperreal? (June, 2011)
  • Fatboy Slim album You’ve Come A Long Way, Baby has an Atari ST in the large foldout picture of Fatboy Slim’s studio.
  • Highly acclaimed electronic music artists Mike Paradinas and Luke Vibert started out writing music on Atari STs.
  • Mike Oldfield’s album Earth Moving’s album notes state that it was recorded using an Atari ST and C-Lab MIDI software.
  • In the Paris performance of Jean-Michel Jarré’s album Waiting for Cousteau, musicians have attached Atari ST machines with unidentified MIDI software to their keyboards, as could be seen in the TV live show and video recordings.
  • White Town’s “Your Woman”, which reached #1 in the UK singles charts, was created using an Atari ST.
  • All the drums MIDI files for The Berzerker’s eponymous debut album were written on an Atari.

1 thought on “The Atari 520ST and various models. . .”

  1. I believe the first disk-based 520s included an RF modulator. It was dropped quickly. I remember when I first wanted one it came with an RF modulator but I knew at the time that the newer ones (i.e., with TOS in ROM) did not.

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