On Sun, 14 Mar 1999, Charles Dye <[EMAIL PROTECTED]> wrote:
> (I am told, however, that early space shuttles used core-memory
> computers. I don't know this for a fact, but it's an... intriguing...
> claim.)
They still do. It took 48k of core to reach the moon in 1969.
Today, most military aircraft use core memory for thier weapons
control computers. ( The US F-4E, which I maintained for 17 years,
contained 32k of core in its "target intercept computer". It was/is
about as fast and as capable as a low-end 386; all of the code was
contained in ROMs, written in the processor's own assembly language.
The processor was specially designed for the purpose, and is totally
unlike any CPU for sale to the public.)
The reason is simple: immunity to radiation/EMP.
While some radiation-hardened static ROMs can survive such things
( the kind of ROMs with microscopic fuses that are "blown" - not
the charge-holding variety in your PC ), very few of today's PC
circuits can hold up to hard radiation.
PCs carried on shuttle missions are not only mil-spec "hardened",
they also are completely excluded from mission-critical applications,
because they cannot be made to meet the specs of zero failure rate
for the duration of the mission.
Core memory is VERY reliable; there are no charges to leak off,
and no power is required to keep the data safe. However, core is
a few thousand times more expensive than RAM, much larger, and
very much heavier.
- John T.
-- Arachne V1.49;beta, NON-COMMERCIAL copy, http://home.arachne.cz/
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