DEC Pro 350/380 Memory Cards - Interchangeability?

Paul Koning paulkoning at
Mon Aug 29 12:10:25 CDT 2016

> On Aug 29, 2016, at 12:33 PM, Rob Jarratt <robert.jarratt at> wrote:
>> -----Original Message-----
>> From: Paul Koning [mailto:paulkoning at]
>> Sent: 29 August 2016 15:08
>> To: rob at; General Discussion: On-Topic and Off-Topic Posts
>> <cctalk at>
>> Subject: Re: DEC Pro 350/380 Memory Cards - Interchangeability?
>>> On Aug 28, 2016, at 5:11 PM, Rob Jarratt <robert.jarratt at>
>> wrote:
>>> I have a 350 and 380. Neither work. The 380 is reporting a possible
>>> memory error on the LEDs. Will the 350's memory work in a 380 (or vice
>> versa)?
>> The 380 has memory on the motherboard, and a model-specific
>> daughtercard for expansion memory.
>> It seems reasonable that the Pro bus (I/O card) expansion memory should
>> work in both models, but I don't have any to try that.
>> If you have a 380 complaining about memory and it has a Pro bus memory
>> card installed, I'd suggest removing that card to see if it's happy with
> just the
>> stock motherboard memory.
>> 	paul
> Just reading your reply again. Are you saying it has enough memory on the
> board, without using a daughter board? I did see lots of memory on the main
> board, but assumed it was video memory. I did try removing the daughter
> board altogether at one point, but it still didn't work. :-(
> I wish I had a logic analyser.

You should get the Pro 300 technical manual (two volumes) from Bitsavers.  It contains a great deal of relevant detail.

From Volume 1, page 4-4 summarizes the system memory for both models. Page 5-129 describes the memory daughter cards of the Pro-350.  Page 6-125 describes the memory daughter cards for the Pro-380.

I misremembered the 350 (I don't have one): it can have memory in the I/O card cage, but it also has memory daughter cards, two of them, with 40 pin connectors.

The Pro-380 has main memory on the motherboard.  It also supports an optional expansion card, just one, with a 48 pin connector.  The pinouts shown for the two types of daughtercards make it very clear that they are entirely incompatible. 

The Pro-380 also has graphics on the motherboard (though EBO is an option, via a daughtercard).  So a Pro-380 with nothing in the I/O card cage should power up and give you a display on the screen (presumably one complaining about not having a bootable device controller...).

On the other hand, the Pro 350 uses a graphics card in the I/O cage, and EBO is a second I/O card connected to the main one via a jumper cable.  Neither of these is compatible with the Pro-380.

I have somewhere a printout (on 11x17 size paper, roughly A3) of the Pro 380 motherboard schematics.  I haven't seen those elsewhere.  I haven't tried to scan them but try if there's interest.


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