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The Atari ST is a family of computers introduced in 1985, built around Motorola‘s 68000 processor. It combined a graphical desktop, color graphics, floppy storage and built-in MIDI ports. The original ST and the later STE look related, but their graphics and sound hardware are not identical.
Atari ST hardware at a glance
| Part | Original ST basics |
|---|---|
| Processor | Motorola MC68000 at about 8 MHz; 16-bit external data bus and 32-bit registers |
| Typical named configurations | 520ST: 512 KB RAM; 1040ST: 1 MB RAM |
| Low-resolution color mode | 320 × 200 pixels, 16 colors chosen from 512 |
| Medium-resolution color mode | 640 × 200 pixels, 4 colors chosen from 512 |
| High-resolution mode | 640 × 400 monochrome, requiring a compatible monochrome display |
| Sound | Yamaha YM2149 programmable sound generator, with three tone channels |
| Music connections | Built-in MIDI In and Out |
| Software environment | TOS operating system and GEM graphical desktop |
These are baseline ST characteristics, not specifications for every machine carrying an Atari name. Atari Corporation’s January 1986 engineering hardware specification describes the processor, display modes, memory organization and music interfaces.
Why the 68000 is described as 16/32-bit
The ST name refers to Sixteen/Thirty-two. The 68000 moves data over a 16-bit external bus and has 32-bit registers and programming features. Its external address bus is 24 bits wide. These are different properties: neither “32-bit” nor the ST name means the original machine had 32 MB of RAM or a 32 MHz processor.
The CPU runs programs, while other chips handle timing, memory access, display output and I/O. A clock-speed comparison alone cannot explain how two different computers perform in a game, a desktop program or a music sequencer.
How the motherboard shares work
| Chip or subsystem | Main job |
|---|---|
| GLUE | Coordinates important system timing and address decoding |
| MMU / memory controller | Organizes RAM access and supplies video-memory addressing |
| SHIFTER | Turns the stored display bitplanes into the pixel stream used for video output |
| DMA controller | Supports transfers between memory and storage interfaces |
| MFP and keyboard controller | Handle tasks such as interrupts, timers and keyboard/mouse communication |
The ST’s chip called an MMU is a memory-control device; it should not be confused with the virtual-memory and process-isolation MMU in a modern CPU. Display memory is part of main RAM. The hardware schedules access between the processor and video system, so “the CPU is blocked whenever video is displayed” is not an accurate description.
Graphics: the palette is larger than the colors on screen
In low resolution, a normal screen selects 16 colors from the ST’s 512-color palette. In medium resolution it uses four. The 640 × 400 mode is monochrome, rather than a higher-resolution 16-color mode. Special software techniques can go beyond a simple static screen, but they are not the baseline mode specifications.
Check the monitor and connection when using original hardware. Color and monochrome modes have different display requirements; an adapter cable does not guarantee compatibility. Our NTSC versus PAL guide also explains why regional video timing needs to be considered separately from a game’s software version.
What changed with the Atari STE?
The STE adds a 4,096-color palette, fine hardware scrolling and stereo DMA sample sound, alongside the existing PSG. It also includes a BLiTTER for certain graphics operations. The BLiTTER was already present in the Mega ST line, so it was not an STE-only invention. A 4,096-color palette means that many selectable colors, not a “4,096-bit” display.
ST and STE software overlap, but an STE-enhanced game or demo can depend on features absent from a plain ST. The later TT and Falcon are different hardware families, not just original ST computers with more RAM. The Hatari project manual separates these machine types and their emulated features.
Why musicians used its MIDI ports
MIDI lets sequencer software exchange note and control messages with synthesizers and other music equipment. It does not send a recorded audio track through the MIDI cable. The original ST’s built-in ports made that connection convenient, while its own YM2149 produced a separate kind of sound. Do not attribute the STE’s stereo DMA audio hardware to every original ST.
Frequently asked questions (FAQ)
Is the Atari ST a 16-bit or 32-bit computer?
It is commonly described as 16/32-bit. Its Motorola 68000 has a 16-bit external data bus and 32-bit registers. The ST name means Sixteen/Thirty-two, rather than its clock speed or amount of RAM.
What is the difference between the Atari ST and STE?
The STE adds features such as a 4,096-color palette, fine hardware scrolling and stereo DMA sample sound. Software that uses those additions may not work the same way on a plain ST. Check the machine type required by the program.
Can you try Atari ST software today?
Hatari emulates ST-family hardware. Select the machine type required by the software rather than assuming the newest model is always the most compatible. Its documentation also describes EmuTOS, an open-source replacement operating system. Original TOS ROMs are not freely bundled with Hatari, and some software depends on a particular TOS version.