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moby
(foldoc) | moby
/moh'bee/ (From MIT, model railroad fans. From
Melville's "Moby Dick", some say from "Moby Pickle") 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."
The maximum address space of a computer. For example, a
32-bit address register can address 4,294,967,296 different
locations or four gigabytes if each location is a byte.
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).
[Jargon File]
(1997-10-01)
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moby
(jargon) | 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).
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high moby
(foldoc) | 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]
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high moby
(jargon) | 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.
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