[ih] when did APRANET -TIPs become known as -TACs

[Steve Crocker]

Jack,

You wrote:

The C/30 microcode was designed to make an MBB look
> exactly like a Honeywell 316.  So the same code that had been developed  for
> the 316-based IMPs (or TIPs) would also run on a C/30.   Effectively, a
> C/30 looked exactly like a Honeywell 316 to the software that ran on it.


Well, almost.

I ran a program verification project for several years.  We used actual
code, i.e. code written by professionals without regard to formal methods,
for our case studies.  For our work on microcode verification, we wrote
formal descriptions of both the micromachine and the macromachine, and then
we attempted to show the microcode implemented the macromachine's
instructions set.

The microcode implementation of the 516 instruction set on the C/30 was one
of our cases.  We found a small set of relatively minor discrepancies.  My
favorite discrepancies for the C/30 were the implementations of the Reset
Overflow Bit and Set Overflow Bit instructions.  The implementations were
reversed.

When we shared our results with the BBN crew, they said they had discovered
the microcode was backwards.  But rather than changing the microcode, they
had changed the assembler.  Big smile.  That's ok if the code for that
machine is guaranteed to be created by the modified assembler.  In the
pantheon of practical solutions that occur in real life, I have no
criticism.

What I hadn't thought about until reading your note is the code for the
Honeywell machines and the C/30 would have been compatible at the assembly
language level but not at the object code level.  Alternatively, I have no
idea if those instructions were actually used in the IMP software.

Steve