Atari 520ST & 1040ST Series

The Atari 520ST and 1040ST were the backbone of the Atari 16-bit line.  These machines made up the bulk of the 16-bit systems produced by Atari.

The name of the Atari ST derives from the nature of its microprocessor, the Motorola 68000.  It is a so-called "sixteen bit /thirty-two bit" processor, hence the name "ST".  It has a 16-bit-wide data bus and 32-bit-wide internal registers.  Though capable of exceptional performance and sporting a rich instruction set, the 68000's 16-bit-wide data path imposes certain restrictions. Most important among these, the chip cannot read a 32-bit quantity from memory in fewer than two bus cycles.  Thus, although the chip's internal data registers and operations accommodate 32-bit numbers, filling them with such numbers requires twice the time it should.  Most 68000 assembly-language instructions are four bytes (32 bits) in length, meaning that the processor requires two bus cycles to read the majority of steps in its own software.  The 68000 also suffers somewhat from the fact that although its address registers and program counter are theoretically 32 bits wide, only 24 of these 32 bits are actually used. The chip is thus limited to addressing a total of 16mb of RAM.

Early 520ST systems did not have the built-in floppy drive, or the operating system (TOS) in ROM.  Those systems would use an external floppy drive, with the OS on disk.  The majority of the ST systems that are out there do have the built-in floppy drive, and some flavor of TOS on the motherboard.  

For the most part, these systems were pretty reliable.  The most common problems that I know of were usually with the mouse.   The Atari mice weren't that sturdy.  They usually had problems with the mouse cable, or the buttons.

Atari ST/STm/STf/STfm System Features:

CPU: Motorola MC68000 16-bit running at 8MHz.

FPU: None

DSP: None

TOS Version: 0.98 on disk (early models only), 1.00 in ROM, 1.02 in ROM or 1.04 in ROM (later models).

RAM: 256kb (very early models only), 512kb or 1Mb, expandable up to 4Mb.

Graphics: 320x200x16 or 640x200x4 using RGB monitor or TV (modulator equipt models only), 640x400x2 using mono monitor. Palette of 512 colors. TV modulator in STm and STfm models. Blitter chip in later STfm models.

Sound: 8-bit mono.

Disk Drives: 360kb external floppy drive (early models only), 360kb internal floppy drive or 720kb internal floppy
drive (later models only).

Ports: Cartridge (ROM) port, MIDI In and Out/Thru, DMA/ACSI port, parallel (printer) port, serial (modem) port running at 19.2 kbps, external floppy drive port, mouse and joystick ports.

Case: One piece standard-style.

Release Date: 1985.