The Raspberry Pi Compute Module line of products are small computers designed to act as the brains of larger devices. Up until a few years ago, they were little boards that basically looked like sticks of laptop memory that you could slide into a larger board using a SODIMM connector. But that changed with the launch of the Raspberry Pi Compute Module 4 in 2020, which featured a new design, a faster processor, and support for features like Gigabit Ethernet, PCI Express, and multiple displays.

Now it looks like Raspberry Pi has a new model that combines the form SODIMM factor of older Compute Modules with some of the features of a Compute Module 4, including the newer, more powerful processor.

Raspberry Pi Compute Module 3+ and Compute Module 4S
Revolution Pi

The new computer-on-a-module is called the Raspberry Pi Compute Module 4S, and it looks a lot like older Compute Modules like the Compute Module 3+ which launched in 2019. But while the CM3+ has a 1.2 GHz ARM Cortex-A53 quad-core processor, the CM4 and CM4+ have the same 1.5 GHz ARM Cortex-A72 quad-core chip found in the Raspberry Pi 4 single-board computer.

Interestingly, the Raspberry Pi Foundation hasn’t officially announced the new CM4S yet, but blogger and YouTuber Jeff Geerling found a description of the new module on the website of Revolution Pi, a company that makes products powered by Raspberry Pi Compute Modules.

The company explains that the new module is a “special alternative” to the Compute Module 3+ that not only has the newer processor, but also has another significant advantage: it’s available.

Raspberry Pi hardware has been in short supply recently, and it’s not just because of the global supply chain issues that have been affecting nearly all aspects of technology manufacturing over the past two years. Raspberry Pi founder Eben Upton explained this week that the organization has also seen a significant increase in demand for its products since 2021, and when you combine increased demand and decreased supply, it’s unsurprising that stores have had a hard time keeping Raspberry Pi computers in stock.

Upton notes that the 28nm BCM2711 processor used in Raspberry Pi 4 series products is easier to source than the 40nm BCM2837B0 used in the Raspberry Pi Compute Module 3+.

Reading between the lines, that means that companies like Revolution Pi, which have already built a line of products designed around the older SODIMM-style Raspberry Pi Compute Modules would be out of luck if Raspberry Pi didn’t release something like the CM4S, which uses the same 200-pin SODIMM connector as older models, making it a drop-in solution.

Because of the connection type, you don’t get all of the advantages of a CM4 in the form factor of a CM3 device though. There’s no PCIe support. You’re limited to USB 2.0 speeds. Ethernet speeds top out at 350 Mbit/s. There’s no WiFi or Bluetooth option. And it’s unclear if you’ll be able to get more than 1GB of RAM.

But the new module has a newer, faster processor, speedier RAM, and support for HDMI 2.0a, even if there’s only support for a single display rather than several.

Here’s a run-down of some key specs for the Raspberry Pi CM3+, CM4S, and CM4:

ModelRaspberry Pi Compute Module 3+Raspberry Pi Compute Module 4SRaspberry Pi Compute Module 4
ProcessorBroadcom BCM2837B0
4 x Cortex-A53 CPU cores @ 1.2 GHz
Broadcom BCM2711
4 x Cortex-A72 CPU cores @ 1.5 GHz
Broadcom BCM2711
4 x Cortex-A72 CPU cores @ 1.5 GHz
RAM1GB LPDDR21GB LPDDR41GB, 2GB, 4GB, or 8GB LPDDR4-3200
StorageUp to 32GB eMMCUp to 32GB eMMC(Optional) 8GB, 16GB, 32GB eMMC
USBUSB 2.0USB 2.0USB 3.0
WirelessN/AN/A(Optional) WiFi 6 and Bluetooth 5.0
EthernetUp to 350 Mbit/sUp to 350 Mbit/sGigabit Ethernet support
Video I/O1 x HDMI 1.3a1 x HDMI 2.0a2 x HDMI interfaces (up to 4K)
2 x MIPI DSI display interfaces
2 x MIPI CSI-2 camera interfaces
PCIeN/AN/APCI Express 2.0 interface
Connector200-pin SODIMM200-pin SODIMM2 x 100-pin mezzanine connectors

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