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

System/360
IBM 360

    The generic name for the CPUs and architecture
   released by IBM on 1964-04-07.  The 360 was marketed as a
   general purpose computer with 'all round' functionality -
   hence 360 (degrees).

   Models ranged from the 360/20 to the 360/65 and later the
   360/95, with typical memory configurations from 16K to 1024K.

   Elements of the architecture, such as the basic instruction
   set are still in use on IBM mainframes today.  Operating
   System/360 (OS/360) was developed for System/360.  Other
   associated operating systems included DOS, OS/MFT and
   OS/MVT.

   The 360 architecture was based on an 8-bit byte, 16 general
   purpose registers, 24-bit addressing, and a PSW (Program
   Status Word) including a location counter.

   Gene Amdahl, then an IBM employee, is generally acknowledged
   as the 360's chief architect.  He later went on to found
   Amdahl Corporaton, a manufacture of PCM mainframe
   equipment.

   The 360's predecessors were the smaller IBM 1401 and the
   large IBM 7090 series.  If was followed by the IBM 370.

   See also ABEND, ALC, BAL, Big Red Switch, HCF, mode
   bit, PL360, PL/S.

   (2004-06-06)