The z9 EC MultiChip Module (MCM) contains 16 chips: Eight are processor chips (supporting 12 or 16 PUs), four are System Data cache (SD) chips, one is the Storage Control (SC) chip, two chips carry the Memory Subsystem Control function (MSC), and there is one chip for the clock (CLK) and ETR receiver function. The 95 x 95 mm glass ceramic substrate on which the chips are mounted has 102 interconnect layers in the substrate and 545 meters of internal wiring. The total number of transistors on all chips on the MCM amounts to more than 4.5 billion.

The MCM plugs into a card that is part of the book packaging, as shown in Figure 2-9. The book itself is plugged into the processor board to provide inter connectivity between the books, so that a multibook system appears as a Symmetric Multi Processor (SMP). The MCM is connected to its environment by 5184 Land Grid Arrays (LGA) connectors. Figure 2-10 on page 41 shows the chip locations.