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Raspberry Pi 4A Could Skip USB 3, Have PCIe Port

Comparison of Raspberry Pi 4 Model B, Raspberry Pi 3A+ and Compute Module 4
(Image credit: Future)

The Raspberry Pi 4 B has been on the market for more than two years and, during that time, we've seen a number of new, related models hit the shelves, including an 8GB Raspberry Pi 4, a Compute Module 4 and the Raspberry Pi 400, which is basically a Pi 4 inside a keyboard. However, there's still been no Raspberry Pi 4 A to displace the Pi 3A+.

However, according to Raspberry Pi CEO and Founder Eben Upton, the company has a lot of ideas for a 4 Model A (aka 4A) and might even have built one already, if not for ongoing chip shortages. Upton joined us on the latest episode of our weekly Pi-centric podcast, the Tom’s Hardware: The Pi Cast and gave us some clues about what a Raspberry Pi 4 A could include and exclude, along with the price point he's looking to hit.

For all three previous generations of Raspberry Pi, there are both B and A models. The more popular Raspberry Pi Model B units have a full suite of four USB ports and up to the maximum amount of RAM. The A units are slightly smaller, have fewer ports and features, and cost a bit less. For example, the Raspberry Pi 3A+ goes for $25 and has just one USB port, along with 512MB of RAM while the $35 Raspberry Pi 3B+ has 1GB of RAM, four USB ports and Ethernet. Putting price aside, some users prefer the smaller form factor and lower power consumption of the 3A+.

“I think it’s something that we might have looked at if we weren’t throwing all the chips we made into (Model) Bs.”, Upton said when we asked about the future of the A line. He later explained that we might have seen a 4A if not for the chip shortage, remakring "I think it’s something that we might have looked at if we weren’t throwing all the chips we made into (Model) Bs."

Upton also spoke about the trade-offs he and his team would have to make to in order to deliver a similar experience to the $35 Raspberry Pi 4 B while hitting a targeted $25 price point.

"If you can't get it to $25 there's not much point in a $30 product, you really have to open up $10 gap," he said, noting that the A models just don't sell as well the B models -- hundreds of thousands versus millions of units -- and that those numbers would be far worse if the scaled-down board wasn't significantly cheaper.

But what could a Raspberry Pi 4 A feature and what could be trimmed from the Bill of Materials (BOM) to keep the cost low? USB 3 is likely at the top of the chopping block. 

Upton explained that “You kind of have to throw out USB 3, right, to get the costs down. You really can’t afford the PCI Express to USB 3 bridge.” The PCI Express to USB 3 in question is the VL805 USB 3.0 controller which provides all of the USB 3 ports for the Pi 4. The removal of this chip would see the Raspberry Pi 4A reduced to USB 2.0 speeds, likely via the previous models LAN9512 / LAN9514 combined USB 2.0 and Ethernet chip. 

The BCM2711 SoC of the Raspberry Pi 4 has a PCI Express lane which is broken out for use on the Compute Module 4 and can be used with 1x PCIe cards via the official IO board. Could this be integrated into the 4A? Upton was unsure if this feature would make it to the 4A “Does it (4A) look like a 3A+ or a 1A+ but it has some sort of PCI Express connector," he asked rhetorically. He also noted that going with one full-size HDMI port over the two micro HDMI ports on the model B could save money and space.

Ideas for the Raspberry Pi 4A were “kicked around” in 2020 / 2021 but sales of other products such as the Raspberry Pi 4 have been at historic highs. As Upton reiterated, “this year literally every single chip that we have is being used to build either Raspberry Pi 4, Pi 400 and Compute Module 4. It would be irresponsible to rob that."

However, should chip shortages ease in 2022, we wouldn't be surprised to see a Raspberry Pi 4A that keeps the same CPU as the Pi 4B, but offers less RAM, USB 2.0 and the possibility of an onboard PCIe port.

Another product that could be coming in 2022 is an updated version of the official Raspberry Pi, 7-inch touch screen. The current model has been on the market for 6 or 7 years and maxes out at a rather-low resolution of 800 x 480 and Upton remarked that it is due for a refresh.

When asked about a potential Raspberry Pi 5, Upton said that his organization isn't working on one right now and is instead prioritizing making improvements to the Raspberry Pi 4 by doing things like updating software. He noted that, when it comes time for a Raspberry Pi 5, it would likely have updated specs such as a faster processor, the ability to have more than 8GB of RAM, quicker USB connectivity, more powerful Wi-Fi and 2.5 Gb Ethernet. 

You can catch new episodes of the Tom's Hardware Pi Cast live every Tuesday at 7:30 pm UK time / 2:30 pm ET on YouTube or Facebook. You can also find all of our previous episodes on YouTube.

Les Pounder

Les Pounder (Associate Editor) is a creative technologist and for seven years has created projects to educate and inspire minds both young and old. He has worked with the Raspberry Pi Foundation to write and deliver their teacher training programme "Picademy".