The Jargon File (version 4.4.7, 29 Dec 2003):

high moby
 /hi:' mohb?ee/, n.

    The high half of a 512K PDP-10's physical address space; the other half
    was of course the low moby. This usage has been generalized in a way that
    has outlasted the PDP-10; for example, at the 1990 Washington D.C. Area
    Science Fiction Conclave (Disclave), when a miscommunication resulted in
    two separate wakes being held in commemoration of the shutdown of MIT's
    last ITS machines, the one on the upper floor was dubbed the ?high moby?
    and the other the ?low moby?. All parties involved grokked this
    instantly. See moby.


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

high moby

   /hi:' mohb'ee/ The high half of a 512K PDP-10's physical
   address space; the other half was of course the low moby.
   This usage has been generalised in a way that has outlasted
   the PDP-10; for example, at the 1990 Washington D.C.  Area
   Science Fiction Conclave (Disclave), when a miscommunication
   resulted in two separate wakes being held in commemoration of
   the shutdown of MIT's last ITS machines, the one on the
   upper floor was dubbed the "high moby" and the other the "low
   moby".  All parties involved grokked this instantly.  See
   moby.

   [Jargon File]