PDP-11/20 in Iowa (x3)

Ethan Dicks ethan.dicks at gmail.com
Mon Mar 27 18:04:49 CDT 2017

On Mon, Mar 27, 2017 at 12:20 PM, Al Kossow via cctalk
<cctalk at classiccmp.org> wrote:
> On 3/27/17 7:37 AM, Systems Glitch via cctalk wrote:
>>> I don't know of MOS memory appearing in 11/20s as built by DEC, but there's no reason against it.
> There were 3rd party cards, Monolithic Systems, for example.
> The problem with the 11/20 is that hex wide cards don't fit, the fans overlap the unibus jumper area.
> If you ever see hex-wide cards with a big notch in one end, they were designed to work in the 11/15 11/20

Exactly.  There are plenty of hex-height cards with MOS memory for
Unibus (I have several for the 11/04 and/or 11/34 of a suitable size)
but they would fit in an external BA11-K or BA11-L w/DD11-DK, not the
CPU's BA11 because of the fans.  That's why I was wondering if DEC
ever made quad-height MOS modules for Unibus or if all DEC-supplied
11/20s and 11/15s had core and only core.


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