[ih] NCP and TCP implementations
steve at shinkuro.com
Tue Mar 10 11:06:45 PDT 2020
To create the TIP, a second bank of memory was added to the 316 and some
interrupts and modes were added to enable switching back and forth between
banks. It was a bit of a kludge with some unexpected interactions. The
BBN crew finally sorted out the details and wrote a delightful titled "It's
Amazing That it Works at all."
On Tue, Mar 10, 2020 at 1:55 PM Bernie Cosell via Internet-history <
internet-history at elists.isoc.org> wrote:
> 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
> > the
> > Honeywell 516 (and later 316) platform, which was a 16 bit twos
> > complement
> > computer. I assume Hinden's reference to 15-bit arithmetic reflected
> > the
> > fact that the arithmetic was signed.
> I honestly cannot remember what the TAC was!! Was that the TIP?
> 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
> 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
> connected host. It'd set up a host output buffer and instead of doing a
> "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
> issue an "interrupt" down to the IMP. Worked quite well.
> Bernie Cosell
> bernie at fantasyfarm.com
> -- Too many people; too few sheep --
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