irwin@uiucdcs.CS.UIUC.EDU (03/11/86)
Core memory as ROM, yes, it will work, but it is a outdated technology.
(I will probably draw some flames here) One might compare it with the
old fashion push type reel lawn mower. There is not much market for
them any more.
One must understand the core memory, and then make a judgement. First,
the core memory takes up a lot of physical space, compared to the latest
and current ROMS. The core is made of ferrite and has a donut shape. It
requires one for each bit, and for however many bits wide the "word" is,
a row of donuts is necessary for each address. When applied, it requires
a "write winding" wound in the core, made up of wire, which requires a
"core driver". Also, there is a "sense lead" which is threaded through
the core. To read the core, one must attempt a write. If the core changes
from it's current magnetic state, the sense wire will sense the change,
so one will know that it's state changed. The sense lead by the way, must
be attached to a "sense amplifier", (one for each sense lead) which will
amplify the tiny pulse induced into the sense lead, to a usable logic level.
If changed on a read, it must be then written back to it's previous state
to preserve the original state.
In other words, to read a core, you actually attempt a write. If it changes
or not tells you what was stored there and if you changed it, you must
then put back what you just altered.
In the "heyday" of core memory, a typical 4096 X 16 bit core plane was
in the order of 6 inches square, not including any electronics.
Core will retain the store when the machine is shut down, so one can think
of it as "ROM". I think however that time required by core and physical
size (added weight in aircraft) and computers no longer the size of a
railroad boxcar, but instead the size of a lunch bucket make it an
outdated memory.
Second, it was a very good memory in it's day, but that day has passed.
P.S. I did NOT cross post this to net.space, we all read both anyway.
Why use up additional disk on everyone's machines?
Ferrite transistors, never heard of them!