The weird stuff I keep finding: 19 bit core memory?

Eric Smith spacewar at
Tue Oct 20 22:39:47 CDT 2020

On Tue, Oct 20, 2020 at 8:06 PM Chris Zach via cctalk <cctalk at>

> The real weird one is a quad board H216. I thought it was a Unibus core
> memory board,

Most of the DEC core plane boards were not specific to any particular bus.
though there are some exceptions.

> but it's 8k*19 bits, which means it came from one place:
> An MA10 memory box. The only one I may have been exposed to was AI (the
> original KA10).

I'm pretty sure the H216 was too new to have been used in an MA10 or MB10,
but I don't know which core planes or other modules were used. They might
have still been using core modules made by external vendors like Ferroxcube.

The much later MF10 does use the H216, while the MG10 uses the H217 and the
MH10 uses the H224.

The H216 also might have been used in memory systems for a PDP-9 (late in
its life) or the PDP-15. The ME15 normally used the H215 18-bit core
planes, but I think there was a parity option, which would have used the

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