The CM3+ Compute Module contains the guts of a Raspberry Pi 3 Model B+ (the BCM2837 processor and 1GB RAM) as well as an optional eMMC Flash device of 8GB, 16GB or 32GB (which is the equivalent of the SD card in the Pi).
This is all integrated onto a small (67.6mm × 31mm) board that fits into a standard DDR2 SODIMM connector. The Flash memory is connected directly to the processor on the board, but the remaining processor interfaces are available to the user via the connector pins. You get the full flexibility of the BCM2837 SoC (which means that many more GPIOs and interfaces are available than with a standard Raspberry Pi), and designing the Module into a custom system should be relatively straightforward because we’ve put all the tricky bits onto the Module itself.
To help you get started designing a PCB to use the Module, we provide an open-source breakout board, which is supplied with both a 32GB and Lite version of the CM3+ in an affordable development kit.