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

GE-645

    A computer built by General Electric, the
   successor to the GE-635, designed to provide the extra CPU
   features required by the Multics project.

   The GE-645 was designed in 1965 by John Couleur and Edward
   Glaser at MIT.  It had several security levels and
   instructions for handling virtual memory.  Addressing used
   an 18-bit segment in addition to the 18-bit address,
   dramatically increasing the theoretical memory size and making
   virtual memory easier to support.

   Design of the GE-645's successor, the GE-655, started in 1967.

   (2006-09-24)