Raspberry Pi goes back to the future with the CM4S

SODIMM fans rejoice – the familiar form factor returns with a speedier CPU


The Raspberry Pi gang will soon ship some new hardware in a form factor to delight builders still mourning the Compute Module 3. Behold the Compute Module 4S.

The Compute Module 4 emerged in 2020 and, as well as featuring some beefier hardware courtesy of the Pi 4, also changed the form factor from the SODIMM of old. While memory could reach the dizzying heights of 8GB and dual HDMI interfaces were available, the departure from that SODIMM form factor of old was a headache for some of the industrial customers at which the unit was targeted.

Jeff Geerling blogged about the new arrival last week, although details on availability outside of Revolution Pi are scant at present.

The major changes between the existing Compute Module 3+ and the 4S consist of the new quad-core Cortex-A72, chugging along at 1.5 GHz and a single 4K HDMI 2.0a output. RAM remains at 1GB, although of type LPDDR4 rather than LPDDR2.

Revolution Pi itself is a modular industrial PC platform based on the Raspberry Pi. Base modules can be expanded via I/O modules and gateways to fulfill a variety of industrial needs. Blaming the global chip shortage, the company last week stated that the standard Compute Modules weren't available, but the Raspberry Pi team was going to release a Compute Module 4S, replete with the BCM2711 of the original CM4.

Rumors were circulating for a while now that an alternative to the full-fat CM4 might be on its way, and eagle-eyed Pi fans noted a GitHub commit referencing the CM4S in December 2021.

With shortages continuing to present a challenge, producing something with components not fashioned from unobtainium would seem to be a prudent move.

Sadly, while the form factor looks to be the same as that of the CM3+, Revolution Pi warned that an update to the 5.10 Linux kernel is needed, meaning that simply plugging in the unit and expecting a speed boost is unlikely to be on the cards.

Revolution Pi expects the first units based on the hardware to ship by the end of April. New orders should be delivered in July.

The Register asked Pi supremo, Eben Upton, about the hardware and he told us: "CM4S was designed at the same time as CM4, to support CM1/3/3+ customers who required a performance uplift, but were unable for whatever reason to convert their products to the newer CM4 form factor."

Upton added: "We made the decision to postpone launch because of supply constraints, but with 28nm parts in a better supply situation than 40nm parts we've recently moved a number of high-volume customers across to the platform."

As for when lower volume customers might get their hands on the kit, Upton told us: "Probably only when the supply situation improves somewhat: it doesn't feel sensible to properly launch new products while we should be focusing on improving the supply situation for the ones we've already launched."

Quite. Last week the Raspberry Pi chief wrote a lengthy post concerning the supply chain challenges faced by the company as demand for the diminutive computers ramped up. ®


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