21 Aug
2002
21 Aug
'02
10:01 a.m.
Dennis Ritchie said:
The 7, 9, 15 were very compatible. I think the -15
had some scheme for using an index register, which
the earlier ones didn't have, but it was otherwise
pretty much identical in IS architecture.
According to Gordon Bell's "Computer Engineering", the primary differences
from the -4 to the -7 were switching from 6-bit to ASCII I/O devices and
the addition of a trap mechanism. The -9 primarily changed the memory
system, going to 2-1/2D core; it was also microcoded. The -15 went to
TTL ICs and added index registers and memory relocation. He says
"The PDP-9 instruction compatibility was acheived with three minor
exceptions about which no complaints were received", although I don't
see an explanation of the exceptions.
http://research.microsoft.com/users/GBell/Computer_Engineering/
--
Roger Ivie
ivie(a)cc.usu.edu