<jargon> /moh'bee/ (From MIT, seems to have been in use among model
railroad fans years ago. Derived from Melville's "Moby Dick", some say from
"Moby Pickle") 1. Large, immense, complex, impressive. "A Saturn V rocket is a
truly moby frob." "Some MIT undergrads pulled off a moby hack at the
2. (Obsolete) The maximum address space of a computer (see below). For a
6800 or VAX or most modern 32-bit architectures, it is 4,294,967,296 8-bit
bytes (four 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. In backgammon, doubles on the dice, as in "moby sixes", "moby ones", etc.
Compare this with bignum: double sixes are both bignums and moby sixes, but moby
ones are not bignums (the use of "moby" to describe double ones is sarcastic).
5. The largest available unit of something which is available in discrete
increments. Thus a "moby Coke" is not just large, it's the largest size on sale.
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 time-sharing 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 six mobies" meaning that
the ratio of physical memory to address space is six, 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 (especially 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 one megabyte of nine-bit bytes).
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