MS11-P MOS memory

The MS11-P (M8743) is a Extended UNIBUS DRAM main memory card. As an EUB card, it can therefore only be plugged into the EUB slots on the PDP-11/24 or PDP-11/44 backplane.

It has ECC which automagically corrects single-bit errors, and detects double-bit errors.

It is a hex-height card, and holds 1 Mbyte when fully populated with 64Kx1 DRAM chips. The memory is arranged as 8 banks, each 16 data bits wide, with 6 additional bits for the ECC.

On power-on, the system is frozen (via negation of the ACLO UNIBUS signal) while the entire memory is cleared, to prevent spurious ECC errors. For diagnostic purposes, the ECC can be disabled, and there are also means for the CPU to read/write the ECC bits directly.