The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The “ST” officially stands for “Sixteen/Thirty-two”, which referred to the Motorola 68000’s 16-bit external bus and 32-bit internals. Due to its graphical user inferface, it was known as the “Jackintosh”, a reference to Jack Tramiel.
The Atari ST was part of the 16/32 bit generation of home computers, based on the Motorola 68000 CPU noted for 128 kB of RAM or more, a graphical user interface, and 3½” microfloppy disks as storage. It was similar to the Apple Macintosh, but lacked many additional features of the Commodore Amiga, though the simpler design did allow the ST to precede the Amiga’s commercial release by almost two months. The Atari ST was also one of the first computers to come with a bit-mapped color GUI, using a version of Digital Research’s GEM released that February.
Info gleaned from Wikipedia