Just a little bit more about CORE memory...
The actual cores were tiny ferrite rings, strung on extremely
thin wire. ( Think of the small grain-of-wheat plastic beads
that kids used to string onto #30AWG wire as part of an "arts
and crafts" project; these were just a bit bigger than memory
cores.)
The things would be physically laid out in an X/Y (or row-and-
column) pattern. In one type, a wire would be passed through
every core on a single row. Another wire would be passed through
the column. This would be repeated for each row and column,
forming the address lines. By passing HALF the current necessary
( to "change" a core's magnetic field ) through both of these
row and column address lines, only the one core which received
both "halves" of the current would switch magnetic fields.
The change was sensed by a single wire which ran through every
core on the (core) plane. It usually was routed down one column,
up the next, down the third column, etc....
One very high-security access system I maintained in 1972 used
a core plane about the same size and shape as an AT motherboard.
It was 1024x1 ram - and the system had 16 of them. A year later,
these were replaced by four 1024x4 cores, each of which was housed
in a metal box about the size of a parallel Zip drive.
By 1976, the airborne ones in the F-4E/G aircraft ( where size and
weight is always a consideration ) packed 32k x 12 into a metal-
encased card about the same dimensions as a "baby AT" motherboard,
but 3/4 in. (2 cm) thick. These are still flying today ( as QF-4s)
and were the "unsung heroes" of the 1990/91 Gulf War. ( F-4G "Wild
Weasel" SAM-killers preceeded the F-117 Stealths into Baghdad.)
BTW - estimates for how long a core retains its "memory" are in
excess of ten thousand years, if undisturbed. ( The sense wires
would probably oxidize to dust by then...)
- John T.
J
-- Arachne V1.49;beta, NON-COMMERCIAL copy, http://home.arachne.cz/
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