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.