Each SIMM consists of 24 each 1 megabit, 20-nSec static RAM chips, along with buffers. The mechanical design is such that they mount at a right angle to the PC board which hosts them (GPS or RUDAK). They are sandwiched with aluminum heat spreaders which also act as additional radiation shields.
The modules are organized so they can serve as 2Mx12 or up to four (4) sections of 1Mx3. This allows their use in the 39-bit-wide GPS memory system or the 12-bit-wide RUDAK memory system.