[ih] NCP and TCP implementations

[Alex McKenzie]

 Bernie et al,
I am quite sure that the C/70 never ran the IMP code.
The MBB was probably funded by ARPA and its development was (I think) recorded in BBN QTRs to ARPA and definitely in other BBN Technical Reports.  But I think the C/70 was a BBN internal (self funded) project and (I think) was not in QTRs.  I do think there was at least one technical paper about the C/70 given at a conference but I can't find any reference, so perhaps not.
Alex

    On Monday, March 16, 2020, 1:28:21 PM EDT, Bernie Cosell via Internet-history <internet-history at elists.isoc.org> wrote:  
 
 On 16 Mar 2020 at 12:31, Noel Chiappa via Internet-history wrote:

> Anyway, on to what I wanted to comment on:
> 
> 
>    > From: Geoff Goodfellow
> 
>    > for some reason when the C/70's came along, TIP's were renamed to
> TAC's
> 
> IIRC, the C/70's were timesharing machines (running Unix, IITC); the
> C/
> machines which were packet switches (IMPs), terminal concentators (TACs)
> etc
> were C/30's. I note from the host tables that the TIP's all seem to have
> been
> H316's, and all TAC's were C/30's.

You're correct.  The TIP was a 316 IMP with the terminal handling code in the 
upper 16K of memory.  The C/30 was an implementation of the 316 on the MBB 
[Microprogrammable Building Block] that BBN had developed.  I have no idea 
about why it was "/30".  The MBB was "microprogrammable" and so we built the 
C/70 -- it was called the "C machine" and the idea what that "C" was its assembly 
language.  I have no idea how that project got started but three of us were 
working on it: Al Nemeth was hacking the Unix kernel,  Carl Howe did the 
microcode and I did a crosscompiler from TENEX to the MBB.

I think it was tagged the "C/70" because it was intended to run Unix as well as an 
11/70 [in practice it worked out to be MUCH faster].  the MBB had 20 bit words 
and Al and Carl were designing a hand-tuned, irregular "instruction set".  Such 
things as a built-in indirect index: he figured out the optimal size of the offset 
field so that referencing part of a 'struct' through a pointer could be done in a 
single instruction not using a register.

There was *NO* regularity to the "instruction set" -- each instruction carved up 
the 20 available bits as seemed most efficient.  We added new/strange 
instructions as we saw fit [e.g.,: Al noticed that almost all subroutine calls in the 
kernel were either zero or one argument calls, and so we had two call 
instructions: the normal one [push push push <call>] and one that *always* 
pushed ONE arg and called in a single instruction.  I had the fun task of putting 
together a C cross compiler running on a 36 bit machine for a 20-bit-word 
machine to handle all that irregularity.

We eventually got the kernel working [with the underlying "instruction set" 
constantly evolving as Al looked at the code the compiler was producing and 
figuring ways to tweak things to make it faster.  Carl and I mostly kept up.  The 
big day [for me, at least] was when I ported the C compiler I"d been working on 
to run natively on the MBB [which involved taking out the 36-bit-ness and 
replacing it with 20-bit-ness].  The Unix kernel compiled on the MBB  and was 
bit-for-bit the same as the image produced on TENEX and we cut the strings to 
TENEX and it was now running solo.  That was pretty much when i left the 
project:  I have no idea [at least no memory] what happened after that [some of 
you might have guessed that I was a bit of a vagabond jack-of-all-trades at BBN: I 
worked on one project or another, got it working and "released" and then I went 
onto the next thing].  I don't remember what *we* called it, but shortly after we 
got it all working it went over to BBNCC and was marketed as the "C/70"

I don't remember its ever running the IMP code.  Alex/Dave: was any of the 
development of the C70 written up?  I wasn't much on writing reports :o)

  /Bernie\



            Bernie Cosell
      bernie at fantasyfarm.com
-- Too many people; too few sheep --
  



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