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

compute server

    A kind of parallel processor where the
   parallel processors have no I/O except via a bus or other
   connection to a front-end processor which handles all I/O to
   disks, terminals and network.

   In some antiquated IBM mainframes, a second CPU was
   provided that could not access I/O devices, known as the slave
   or attached processor, while the CPU having access to all
   devices was known as the master processor.

   (1995-03-19)