moby /moh'bee/
[MIT: seems to have been in use among model railroad fans
years ago. Derived from Melville's "Moby Dick" (some say from
`Moby Pickle'). Now common.] 1. adj. Large, immense, complex,
impressive. "A Saturn V rocket is a truly moby frob." "Some MIT
undergrads pulled off a moby hack at the Harvard-Yale game." (See
Appendix A for discussion.) 2.
n. obs. The maximum address space of a machine (see below). For a
680[234]0 or VAX or most modern 32-bit architectures, it is
4,294,967,296 8-bit bytes (4 gigabytes). 3. A title of address
(never of third-person reference), usually used to show
admiration, respect, and/or friendliness to a competent hacker.
"Greetings, moby Dave. How's that address-book thing for the Mac
going?" 4. adj. In backgammon, doubles on the dice, as in `moby
sixes', `moby ones', etc. Compare this with bignum (sense 3): double sixes are both bignums
and moby sixes, but moby ones are not bignums (the use of `moby'
to describe double ones is sarcastic). Standard emphatic forms:
`Moby foo', `moby win', `moby loss'. `Foby moo': a spoonerism due
to Richard Greenblatt. 5. The largest available unit of something
which is available in discrete increments. Thus, ordering a "moby
Coke" at the local fast-food joint is not just a request for a
large Coke, it's an explicit request for the largest size they
sell.
This term entered hackerdom with the Fabritek 256K memory
added to the MIT AI PDP-6 machine, which was considered
unimaginably huge when it was installed in the 1960s (at a time
when a more typical memory size for a timesharing system was 72
kilobytes). Thus, a moby is classically 256K 36-bit words, the
size of a PDP-6 or PDP-10 moby. Back when address registers were
narrow the term was more generally useful, because when a
computer had virtual memory mapping, it might actually have more
physical memory attached to it than any one program could access
directly. One could then say "This computer has 6 mobies" meaning
that the ratio of physical memory to address space is 6, without
having to say specifically how much memory there actually is.
That in turn implied that the computer could timeshare six
`full-sized' programs without having to swap programs between
memory and disk.
Nowadays the low cost of processor logic means that address
spaces are usually larger than the most physical memory you can
cram onto a machine, so most systems have much less than
one theoretical `native' moby of core.
Also, more modern memory-management techniques (esp. paging) make
the `moby count' less significant. However, there is one series
of widely-used chips for which the term could stand to be revived
-- the Intel 8088 and 80286 with their incredibly brain-damaged segmented-memory designs.
On these, a `moby' would be the 1-megabyte address span of a
segment/offset pair (by coincidence, a PDP-10 moby was exactly 1
megabyte of 9-bit bytes).