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The design of the CM4 is loosely based on the Raspberry Pi 4, Model B, and for cost sensitive applications it can be supplied without the eMMC fitted; this version is called the Raspberry Pi Compute Module 4 Lite (CM4Lite).
While previous generations of the Compute Module have all shared the same DDR2-SODIMM-mechanically-compatible form factor, the new CM4 and CM4Lite are different.
The electrical interface of the CM4 is via two 100-pin high density connectors, and the new physical form factor has a smaller footprint overall when the connectors are taken into account.
This change is due to the addition of new interfaces; an additional second HDMI, PCIe, and Ethernet. The addition of these new interfaces, especially PCIe, would not have been possible while preserving the previous form factor.
