The Free On-line Dictionary of Computing (30 December 2018):

Atari ST

    A personal computer released by Atari in 1985.
   The "ST" stands for "Sixteen/Thirty-two", from the Motorola
   68000's 16-bit external bus and 32-bit processor.  The
   original 520ST model had an external floppy drive and power
   supply whereas the 1040ST had them built-in.  The 520 and
   later 520STFM came with 512 KB of RAM, the 1040 had 1 MB.
   Several upgraded models followed, up to the 1993 Motorola
   68030 based Falcon.

   The ST was the first home computer with built-in MIDI ports
   and plenty of MIDI software.  A wide range of other software
   from office to games was also available.

   (2006-10-30)