[ih] Intel 4004 vs the IMP

[Jack Haverty]

IIRC, another of the important criteria for selecting the Honeywell 516 
was the I/O performance characteristics, since much of what the IMP did 
was transmit and receive over multiple interfaces (to hosts as well as 
modems) simultaneously.   The interrupt scheme was part of the larger 
issue of I/O capability.

So in looking for the earliest "comparable" microprocessor, in addition 
to comparing metrics such as CPU speed and memory, I think you have to 
look at I/O characteristics, and how good the processor was at moving 
data in and out of multiple serial interfaces simultaneously.

/Jack Haverty


On 11/15/21 12:21 PM, Alex McKenzie via Internet-history wrote:
>   BBN chose the 516 because of its interrupt structure (as you remember) and because it came in a ruggedized cabinet.  We chose the 316 as a follow-on version because it was program-compatible and cheaper.  The fact that the manufacturer was close to BBN and willing to build interfaces to BBN's design (and provide field service for them) was also a factor.
>
> Cheers,Alex
>
>      On Monday, November 15, 2021, 03:09:02 PM EST, John Levine via Internet-history <internet-history at elists.isoc.org> wrote:
>   
>   It appears that Clem Cole via Internet-history <clemc at ccc.com> said:
>> The instruction set <https://en.wikipedia.org/wiki/Instruction_set> had 72
>> arithmetic, logic, I/O and flow-control instructions.
>>
>> What I don't remember is the clock frequency, but I think it was in the
>> order of .5-1Mz.  It used core which teneded to be slower than
>> semiconductor memory at the time.
> Here's a handy programmer's reference that tells us that the memory cycle time, which tended
> to be the limit on performance in that era, was 1.6us on the 316 and 960ns on the 516:
>
> http://bitsavers.org/pdf/computerControlCompany/series16/h316/70130072156_316_516_PgmrRef_Nov70.pdf
>
> I was under the impression that they chose the 316 because it had a multi-level priority interrupt
> which was unusual at the time.  There were a lot of 16 bit minis available in 1969 such as the HP2100,
> DG Nova, and Lockheed Mac16, and the 316 was otherwise quite a me-too machine.
>
> R's,
> John