Hand-wired core for ROM?

[Noel Chiappa]

    > From: Brent Hilpert

    > Core rope ROM has one magnetic core per the word-width of the memory.
    > That is, a memory of (say) 1024 16-bit words would have 16 cores.

Not always (although your basic point, that in core ROM, a single core is
often/usually used for more than one bit, is a very key point to note); the
Apollo rope ROM had one core per 192 bits, or 12 words of 16 bits each,
"thousands of ... cores" per memory rope. See:

  http://web.mit.edu/digitalapollo/Digital%20Apollo%20Annotated.doc

and there's a picture of one here:

  http://klabs.org/mapld04/presentations/session_g/g1007_hall_s.ppt

(see slide #15).

Those notes do contain an interesting aside: "rearrange the program's
fixed-memory allocations to avoid cases where such sets of 12 words contained
too many ones to fit in their cores", which implies that the cores were
fairly small, physically (since a one involved running the wire _through_ the
core, not around it).

I don't know why they didn't make the cores larger, and have fewer of them;
my suspicion is that in manufacturing terms, it was easier to have more of
them, with less wires through each one. (I can't think of an _electrical_
reason to do so; unlike with RAM cores, where smaller cores are faster to
switch, and take less power to do so.)

	Noel