MM11-E and MM1-F core memories

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The MM11-E and MM11-F core memories were UNIBUS main memory units; the first UNIBUS memories produced by DEC. They came out with/for the first PDP-11, the PDP-11/20.

They were very similar - both 4K word (8K bytes), and with most of their boards in common. The MM11-F was capable of interleaving (although this capability was then made available to the MM11-E as well); it also had a parity version available, the MM11-FP (which used a 4Kx18 core plane, instead of the 4Kx16 used in the MM11-E and MM11-F).

The MM11-F was also slightly faster: the MM11-E had an access time of 500 nsec and a cycle time of 1.2 μsec; the MM11-F had an access time of 400 nsec and a cycle time of 980 nsec.

Both consisted of a quad-width H207 (non-parity) or H210 (parity) core plane board, along with a number of dual- and single-width cards (all extended-length), plugged into a custom-wired quad system unit. The MM11-F and MM11-FP used the same backplane; only the board set was slightly different

Board locations

These are the board locations for the MM11-E, -F and -FP (as seen from the board side of the backplane):

Connector Slot 4 Slot 3 Slot 2 Slot 1
A UNIBUS
Out
Power   UNIBUS
In
B G225% M109!
C H207
or
H210
G226 G226 M729@
or
M7290%
D G102 G102
E G102 G102 ++
F G226 G226 G103

++ = G225 (MM11-E) or G108 (MM11-FP)
@ = MM11-E only
% = MM11-F and -FP only
! = Possibly the later M1091

The M1091 could be used in the MM11-E as well as the MM11-F; it appears that later units of the MM11-E shipped with the M1091. The difference between the M109 and M1091 is the addition of additional jumpers to allow interleaving.