moby

(jargon)/moh'bee/ (From MIT, seems to have been in useamong 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 mobyfrob." "Some MIT undergrads pulled off a moby hack at theHarvard-Yale game."

2. (Obsolete) The maximum address space of a computer (seebelow). For a 680[234]0 or VAX or most modern 32-bitarchitectures, it is 4,294,967,296 8-bit bytes (fourgigabytes).

3. A title of address (never of third-person reference),usually used to show admiration, respect, and/or friendlinessto a competent hacker. "Greetings, moby Dave. How's thataddress-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 sixesare 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 availablein 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 memoryadded to the MIT AI PDP-6 machine, which was consideredunimaginably huge when it was installed in the 1960s (at atime when a more typical memory size for a time-sharingsystem was 72 kilobytes). Thus, a moby is classically 256K36-bit words, the size of a PDP-6 or PDP-10 moby. Back whenaddress registers were narrow the term was more generallyuseful, because when a computer had virtual memory mapping,it might actually have more physical memory attached to itthan any one program could access directly. One could thensay "This computer has six mobies" meaning that the ratio ofphysical memory to address space is six, without having to sayspecifically how much memory there actually is. That in turnimplied that the computer could timeshare six "full-sized"programs without having to swap programs between memory anddisk.

Nowadays the low cost of processor logic means that addressspaces are usually larger than the most physical memory youcan cram onto a machine, so most systems have much *less* thanone theoretical "native" moby of core. Also, more modernmemory-management techniques (especially paging) make the"moby count" less significant. However, there is one seriesof widely-used chips for which the term could stand to berevived --- the Intel 8088 and 80286 with their incrediblybrain-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 ofnine-bit bytes).

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