Raspberry Pi CM3E joins CM4S in the old SO-DIMM form factor

Last week this Tweet crossed my timeline:

If you look closely, that's a "Raspberry Pi Compute Module 3E"—which is so far not listed on Raspberry Pi's website.

New Raspberry Pi: Compute Module 4S

Update: The Compute Module 4S is now listed on Raspberry Pi's website. But they state it "is not for general sale."

Strange times beget strange things.

And that's an apt description of the new Raspberry Pi Compute Module 4S:

Raspberry Pi Compute Module 3+ to 4S Differences

The above chart is from Revolution Pi's page announcing the RevPi S and SE, which are updates to their popular CM3+-based industrial DIN rail computers.

Pine64 and Radxa's new Pi CM4-compatible boards

Since the Raspberry Pi was introduced, hundreds of clones have adopted the Pi's form factor (from the diminutive Zero to the 'full size' model B). Often they have better hardware specs, and yet they remain a more obscure also-ran in that generation of Single Board Computer (SBC).

Pine64 SOQuartz and Radxa CM3 in front of Raspberry Pi Compute Module 4

So when I saw Radxa's CM3 and Pine64's SOQuartz, I wanted to see if either would be—as they advertised—'drop in, pin-compatible replacements' for the Raspberry Pi Compute Module 4.

tl;dr: They're not. At least not yet.

Hardware and Specs

Both boards are technically pin-compatible. And both will boot and run (to some extent) on pre-existing Compute Module 4 carrier boards, including Raspberry Pi's official IO Board: