Original PDP-11/10 [was: Re: Origin of 'Straight 8' name]

Paul Koning paulkoning at comcast.net
Fri Dec 21 18:37:29 CST 2018

> On Dec 21, 2018, at 7:15 PM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:
> ...
>> From: Paul Koning
>> I'm curious about that 1 kW read-only memory. What technology is that
>> memory? At that size and that date I suspect core rope, but that would
>> be pretty expensive (due to the labor involved).
> I think that's what it must be. It's the MR11-A, about which I can find very
> little - it's in the 1970 "pdp11 handbook", p. 46, but I can't find anything
> else.
> It says there "2-piece core with wire braid, 256 wires, 64 cores". Reading
> between the lines, it sounds like the customer could 'configure' the contents
> (perhaps using the "2-piece core), DEC didn't do it.
> If anyone knows anything about this memory, that would be really good.
> 	Noel

That description makes it sound like transformer memory (cores operating as linear devices), as opposed to be square hysteresis loop memory such as conventional core RAM as well as Apollo or EL-X1 core ROM.

Brent Hilpert wrote a good explanation of the various kinds.  The "transformer" type he describes is the Wang calculator microcode ROM.

For 1k by 16, core rope memory would use more cores but fewer wires.  And it might be slower because (in the Apollo flavor at least, which is the one DEC would be likely to know about since it came from Lincoln Labs) it takes a two-part cycle to read a word.


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