Raspberry Pi Compute Module 4S Mysteriously Revealed?

Mock up of the Compute Module 4S
(Image credit: Raspberry Pi / Karolina Grabowska)

A new version of the Raspberry Pi Compute Module 4 may be on the horizon, and it could be returning to the SO-DIMM form factor of its forebears. Known as the Raspberry Pi Compute Module 4S, the possible new board was announced on Twitter (opens in new tab) not by Raspberry Pi itself, but by Nicolai Buchwitz of German industrial control unit manufacturer Revolution Pi, having appeared silently in the Raspberry Pi Github (opens in new tab) back in December.

Apparently a 200 pin SO-DIMM board like the Compute Module 3+, but containing at least some of the uprated components of the Compute Module 4 (opens in new tab), the CM4S was immediately the subject of discussion (opens in new tab) on the Raspberry Pi forum, with a thread started by Pi-watcher and friend of the Tom’s Hardware The Pi Cast (opens in new tab), Jeff Geerling, who also made a video about it.

Revolution Pi’s claim is that the 4S board is at the heart of its new S and SE series products, used in industry to control, monitor, and automate processes. It gives the specs of the CM4S as broadly in line with what we’d expect, with a Broadcom quad-core Cortex-A72 CPU at 1.5GHz, 1GB of RAM, up to 32GB of eMMC flash, HDMI 2.0a and Ethernet up to 350Mbit/s in a 68 x 31 x 4.7mm package with a single SO-DIMM edge connector. Using the SO-DIMM connector over the Compute Module 4's dual 100 pin board-to-board connectors means that the Compute Module 4S will not have access to PCIe or Gigabit Ethernet, but it could be a drop in replacement for industrial customers wishing to upgrade their existing kit.

On its web page, Revolution Pi makes much of the global chip shortage as to why its products, based on the Compute Module 3+, have not been available. It claims that “The Raspberry Pi organization has therefore offered us a special alternative to the Compute Module 3+: The Compute Module 4S. This is a Compute Module in the form factor of the CM3+, on which the more powerful Arm Cortex-A72 processor of the CM4 is installed”.

The news comes on the back of a statement (opens in new tab) by Raspberry Pi co-founder Eben Upton on stock issues among the various iterations of the popular single-board computer, with the recommendation that prospective purchasers consider the Raspberry Pi 400 (opens in new tab) and Pi Pico (opens in new tab) packages, as these have the most availability. As stock of the older Raspberry Pi models dwindles, and Raspberry Pi also prioritizing industrial and commercial customers, now could be the time for those customers to upgrade to a newer Pi. The Compute Module 4S could be a cost effective alternative, requiring no re-work of any bespoke PCBs or carrier boards. There have been other attempts to use SO-DIMM form factors with the Compute Module 4, most notably Gumstix's range of adaptors. As Geerling mentions in the video, these boards are often have hit-or-miss compatibility. 

We have reached out to Raspberry Pi Ltd for confirmation and details of the new board, and will update this story when we get new information.

Ian Evenden
Freelance News Writer

Ian Evenden is a UK-based news writer for Tom’s Hardware US. He’ll write about anything, but stories about Raspberry Pi and DIY robots seem to find their way to him.