DEC M705 vs M7050 in PC05

[Johnny Billquist]

On 2015-07-29 19:08, Jack Rubin wrote:
> If you were following Joerg Hoppe's recent PC05 auction on eBay, you might have noticed that his system had an M705 in the backplane where I would have expected an M7050. This is the way he received it and the restored unit works as it should.
>
> Clearly the cards are similar but different but are they interchangeable? Would the backplane wiring be different and if so where would this be recorded?
>
> My copy of the PC04/05 maintenance manual (DEC-00-PCOA-D(1)) makes no mention of the M705 in this location. The PC04/05 print set on Bitsavers has the M705 on the module utilization list (p45) but crossed out with no reference notes. There is an ECO list on the sheet, showing PC05 ECO's 3, 16 and 30 but no specifics. Is there an available ECO log that would cover these notes?
>
> Then there's the K303, but that's another story...

Don't know any specifics here, but I know that DEC made improved cards 
in many cases, where they added a 0 at the end of the improved card.

Examples:
M454 - M4540
M596 - M5960
M930 - M9300

There are also examples where the zero was added, and the new module 
replace a set of modules that combine to implement a device.

These are PDP-11 examples, you can find even more of this on the PDP-8 
side of things.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
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