IBM 4381 Manual page 26

700 by 600 millimeters (27.6 by 23.6 inches) in size and 4.6 millimeters (about
1/4 of an inch) thick (the same size as the TCM board in a 308X Processor Unit).
The MCM board has 22 module positions and is shown in Figure 4 on page 18.
Figure 5 on page 18 shows how MCMs are mounted on the MCM board.
Figure 3. A 64-mm MCM being hand held
The instruction processing logic for 4381 Processor Model Groups 11, 12, and 13
(exclusive of that for the support processor subsystem and some channel functions)
is contained in 22 MCMs and these modules are mounted on one MCM board.
The 4381 Processor Model Group 14 contains two MCM boards. The fully loaded
MCM board weighs 37 kilograms (81.4 pounds). The MCM board has 8 layers for
interconnecting the circuits on the MCMs and contains 1435 meters (about 4707
feet) of wiring for circuit interconnections. Figure 6 on page 19 shows the MCM
board as it is mounted on its side within the frame of a 4381 Processor.
Since all instruction processing logic is contained on one board in a 4381 Processor
Model Group 11, 12, or 13, interboard cabling for logic is eliminated, which
increases logic speed and reliability. In the 4341 Processor, two boards are
required for logic and 400 cables are used for circuit connections between the two
boards. For a 4381 Model Group 14, some cabling between the two MCM boards
is required for communication between the two instruction processing functions.
The standard card-on-board approach (a 22-card board) is used for other
functional components of the 4381 Processor. There is one processor storage
board, one board to support certain channel functions, and two boards for support
processor components.
Section 10: Technology and Architecture
1 7