3 Nov
2005
3 Nov
'05
4:46 p.m.
On 11/3/2005 at 4:31 PM a.carlini at ntlworld.com wrote:
Apparently one of the US three-letter-agencies asked
for some modifications to (IIRC) the proposed PDP-10
instruction so that it would do whatever they wanted
a tad more quickly. counting-1s was (again, IIRC) one
of those requested additions.
...and then there are the machines whose designers freely gave in to such
requests. The CDC Star-100 is one such. You need an instruction, you've
got it. BCD arithmetic (to 65K digits), masked byte key searches,
approximate compare instructions, etc. etc., they were all there. Very few
people knew the entire instruction set (there were modifier bits for many
instructions and the effects of those could range from subtle to downright
bizarre). One of the big changes in the 100C from the original 100 was the
reduction in size of the instruction set--I know of no other machine where
later models actually de-implemented on a wholesale basis whole classes of
instructions. The other improvement was the incorporation of a scalar
arithmetic unit, so that scalar operations weren't effectively executed as
1-element vectors.
Cheers,
Chuck