19 Dec
2005
19 Dec
'05
6:37 a.m.
William Donzelli wrote:
The original run of Crays (Cray-1, -1M and 1S) were
made from a very small
number of types. I think the original was made with just four different
chips in very large numbers: some simple gates, some more simple gates, a
flipflop, and a memory cell.
Pretty dumb idea, but Cray often "had to be different". I think the
original machines could have benefitted by using a wider range of parts
(like MECL III) - certainly the chip count would have gone way down.
I recall reading that the Cray-1 used balanced logic circuits, in which
a complementary pair of a signal and its complement were always
generated, and each fed a terminated transmission line. The idea was
that the machine drew essentially constant current regardless of its
logic state. Perhaps this placed constraints on the chips that could be
used, as most MSI functions are not implemented in such a perfectly
symmetric fashion.
--Bill