MS11-K MOS memory
The MS11-K MOS memory modules were the first generation of memory array modules used in the MK11 memory system for the PDP-11/70. (The functional difference between the 256KB version of the MS11-K, and the later M8728, is currently unknown.)
Each MS11-K module was a hex board, the M7984. Fully populated, the board holds a total of 156 DRAM chips, including 28 to hold the ECC. According to the prints, it could be used with 4Kx1 chips, giving 64KB total storage; or 16Kx1, giving 256KB.
Per the prints, these are the configurations and board types:
|M7984-Ax||MS11-KA||64KB||156 x 4K chips|
|M7984-Bx||MS11-KB||32KB||78 x 4K chips|
|M7984-Cx||MS11-KC||256KB||156 x 16K chips|
|M7984-Dx||MS11-KD||64KB||39 x 16K chips|
|M7984-Ex||MS11-KE||64KB||156 x 4K chips|
|M7984-Fx||MS11-KF||128KB||78 x 16K chips|
(The 'x' in the board number is one of a number of letters, starting with 'A', which indicates the manufacturer of the DRAM chips used.)
It is not confirmed exactly what the difference is between the -KA and the -KE; the prints show the latter as a replacement for the former, and describe the latter's RAM chips as "fast RAM" (200nsec versus 75nsec).