The Compute Module 4 (CM4) is a the latest addition to Raspberry Pi family.

Essentially it's a Raspberry Pi 4B without the physical LAN and USB I/O as shown on the right. You can see it's smaller and uses a new form-factor but the set of chips look familiar.

CM4 is not intended as a stand-alone product. Instead, it is a System on Module (SoM) containing processor, memory, eMMC Flash and supporting power circuitry. It is designed to be embedded into custom systems and as such it's a perfect fit for bespoke designs BitScope creates for its customers.

Compute Module is available in two version one with (CM4) and one without (CM4Lite) eMMC.

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 new modules have extra IO interfaces over and above what is available on the Raspberry Pi boards, opening up more options for the designer.

The connectors for these new interfaces located on the under-side of the module via two 100-pin high density connectors. The new physical form factor has a smaller footprint overall when the connectors are taken into account. This change has enabled the addition of the second HDMI a single lane PCIe and Ethernet, all on the module. The addition of these new interfaces, especially PCIe, would not have been possible while preserving the previous form factor.

To make designing with CM4 easier Raspberry Pi have created Compute Module 4 IO Board (CM4IO) It contains many of the interfaces that the Raspberry Pi 4B has and for general usage you should refer to Raspberry Pi 4B documentation.

The most significant difference between CM4IO and Raspberry Pi 4B is the addition of a single PCIe socket. The CM4IO has been designed as both a reference design for CM4 or to be used directly as a product with the possible addition of PCIe Cards and Raspberry Pi HATs.

Raspberry Pi have produced these neat videos about the product:

They have also published the following datasheets that describe the modules and the I/O board in detail.

CM4 BRIEF	CM4 I/O BRIEF
CM4 DATA SHEET	CM4 I/O DATA SHEET

You may be wondering how does this new Raspberry Pi relate to BitScope?

CM4 enables us to spin custom designs for our commercial customers that combine the best of what Raspberry Pi has to offer with BitScope's embedded data acquisition and analysis solutions. We are also reviewing it for use at the core of some new edge compute products.

Bottom Line: when it comes to an off-the-shelf and complete embedded computing solution, that's low cost, easy to use, available everywhere and very well supported Raspberry Pi 4B retains the title of industry's best solution.

However, for designs that are deeply embedded for which direct access to PCIe is vital CM4 is the ideal choice.

JK42A