[Simh] pdp11 and unix

[Paul Koning]

> On Feb 27, 2016, at 5:49 PM, Dave Wade <dave.g4ugm at gmail.com> wrote:
> 
>> 
>> BTW, I think that plugboard programming, other than for some business
>> applications with IBM "accounting machines", disappeared rather quickly as
>> Von Neumann machines appeared.  That too would be interesting to look
>> for.
> 
> I am not so sure about that. Older technology often continued in use long after it was produced. In the 50's, 60's and 70's they took the "if it ain't broke don't fix it" paradigm seriously.
> 
> So IBM punch card accounting machines, complete with plug boards were still in use in 1974 when I did my "Industrial placement" at a Life Insurance Company. I was taught Analog Computer programming, using of course plug boards. Some not so early mini computers used "ferrite core rom" where you dropped a ferrite core into a coil to set a bit.

What I meant by "disappeared" is that they weren't used in newer designs any longer.  Yes, some people kept using old computers for a long time.

One category of core ROM has cores for each bit, with address lines either threaded through the hole for one, or around it for zero.  Presumably you'd do this for fairly modest ROM sizes, otherwise the wire mess would get out of hand.  The EL-X1 had its loader and "BIOS" in that kind of ROM, about 900 words.

	paul