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[ih] NCP and TCP implementations
On 10 Mar 2020 at 13:23, Steve Crocker via Internet-hi wrote:
> The TAC was an extension of the IMP. The original IMP was built on
> Honeywell 516 (and later 316) platform, which was a 16 bit twos
> computer. I assume Hinden's reference to 15-bit arithmetic reflected
> fact that the arithmetic was signed.
I honestly cannot remember what the TAC was!! Was that the TIP? Regardless,
yes, the x16s had 16-bit signed arithmetic with 10 bit addressing 9 bits of page
address, 1 bit of "this page" or the 0 page, 16Kwords of memory.
Things got more complicated with the 316 -- it supported 32K words. What we
did for the TIP [and maybe the TAC, whatever that was] was to keep the IMP
*unchanged* in the bottom 16K, and then in the upper 16K we wrote a
self-contained "host". There was some [small!] hack to fake interrupts and
input/output to this host but to the IMP it thought it was just another NCP
connected host. It'd set up a host output buffer and instead of doing a hardware
"send" it'd pass control to the upper 16K. Similarly [at least for the TIP], when it
got something in from a terminal it'd copy it into a host-input buffer and then
issue an "interrupt" down to the IMP. Worked quite well.
bernie at fantasyfarm.com
-- Too many people; too few sheep --