MEM11 Status Update

Noel Chiappa jnc at
Tue Jan 20 08:09:59 CST 2015

    > From: Guy Sotomayor

    > a multi-function Unibus board that contains all of the more difficult
    > items to allow a PDP-11/20 to run Unix V1 entirely within the CPU
    > chassis. Other than the CPU and the RK11-D controller, everything else
    > will be on the MEM11 board.
    > ...
    > What's on the board is the following:
    > ...
    > RF11 controller with non-volatile memory emulating 8 RS11 drives

What form is the NVM in - an SD card, or just a chip, or what? I assume it's
flash memory of some kind? (What's the limit on the number of write cycles
with current flash memory, I wonder...) BTW, a removable card would be great
- that would provide a way to get bits into the machine, other than loading
them all in over a serial line.

I'm kind of curious about your decision to only have an RF11, given the
capacity of contemporary flash memory chips/cards. Why not an RK11 too? (You
may have plenty of RK controllers/drives, but some of the rest of us aren't so
lucky... :-) Is there not enough room in the 16K code block to do that too?
And how about an RP11 too, for those of us running these cards in later
PDP-11's? :-)

(Oh, speaking of the 16K limit - any way to increase the size? Probably not
without munging the J1 architecture, I would guess - I need to go grab it and
read it. But limited addresses spaces always turn out to bit you where it
hurts... :-)

    > As I was competing the configuration UI, I found that I couldn't have
    > both the configuration UI and the emulation code both fit in 16K
    > (strings take up a lot of space).

I seem to recall this problem from my days of writing packet switches for
PDP-11's... :-) The code was famous for log messages that left out all the
vowels, to save space.. :-)

Please, make the UI as cryptic as needed to make all the features (e.g. more
disk controllers :-) fit - documentation can explain what all the cryptic
names are. (Or perhaps even a front-end running on a PC which is connected to
the MEM11 over the serial line.)

Don't take any of this to mean I don't think this is really, really neat, and
very impressive - it's both! Needless (perhaps) to say, I'll be buying a stack
of these when they are ready! :-)


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