The Atari 520ST, saw limited release in April–June 1985 and was widely available in July. The 520ST is the first personal computer to come with a bitmapped color GUI, using a version of Digital Research's GEM released in February 1985. The 1040ST, released in 1986, is the first personal computer to ship with a megabyte of RAM in the base configuration and also the first with a cost-per-kilobyte of less than US$1.

The Atari ST is part of a mid-1980s generation of home computers that have 16 or 32-bit processors, 256 KB or more of RAM, and mouse-controlled graphical user interfaces. This generation includes the Macintosh, Amiga, Apple IIGS, and in some markets the Acorn Archimedes. "ST" officially stands for "Sixteen/Thirty-two", which refers to the Motorola 68000's 16-bit external bus and 32-bit internals. The hardware was so similar to Apple's Macintosh at the time that with the addition of the Spectre GCR the ST was able to run Macintosh software faster than an actual Mac Plus at the time (since the Atari's clock speed was higher) and with a larger and higher resolution display. In fact, the Stacy (the laptop version of the Atari ST) was the first and only way to own a laptop running Mac OS at the time since Apple did not offer one until much later.

The ST was sold with either Atari's color monitor or the less expensive monochrome monitor. The system's two color graphics modes are only available on the former while the highest-resolution mode needs the monochrome monitor.