The newest Raspberry Pi has some big architectural changes
The final iteration of the ‘classic’ Raspberry Pi was released at the tail end of last year. An evolution rather than a revolution, both the Raspberry Pi 3 Model B+ and Model A+ boards wrung the last bits of available performance out of the platform, and it was clear that the Foundation would have to do something rather different the next time around.
We were all anticipating that this would take some time, so most people weren’t really expecting a new and updated Raspberry Pi until sometime next year. So the announcement early this morning by the Foundation might well have caught a few people by surprise.
Despite looking on the surface a lot like previous Raspberry Pi models, the new Raspberry Pi 4 is a very different beast, and just as we’d expected, there are some radical architectural changes here from earlier Raspberry Pi boards.
It seems pretty obvious that the hardware team at the Foundation started out with a whiteboard full of all the complaints that people continuously make about the Raspberry Pi, and then set out to fix every one of those complaints.
Personally, I think they might well have succeeded.
The encapsulated processor, which uses the same heat spreader for better thermal control as the last model, may look the same from the outside. But while the Raspberry Pi 3 was built around the Broadcom BCM2837 processor, a quad-core ARM Cortex-A53 clocked at 1.4GHz, the new board is built around the Broadcom BCM2711, a 64-bit quad-core ARM Cortex-A72 clocked at 1.5GHz. While that might not seem significant, there are some big differences between the core architectures of the these two processors.
While the A53 was designed as a mid-range core, and for efficiency, the A72 is a performance core, so despite the apparently small difference in clock speed, the real performance difference between the cores is really rather significant.
“We’ve always seen ourselves as a PC company, and each generation of Raspberry Pi hardware has brought us closer to being a no-compromises platform. With a speedup of 2–4× over its predecessor, and options for up to four times as much memory, Raspberry Pi 4 is the product that finally takes us over the line. For the vast majority of users the subjective experience of using this new product is that of using a PC.” — Eben Upton, Founder, Raspberry Pi Foundation
The new Raspberry Pi 4 runs a lot faster than you’d expect, more than fast enough that it’s a viable desktop replacement for your average user.
USB and Ethernet
However probably the most noticeable difference from previous models is that the Microchip LAN7515, which acted as the USB hub and an Ethernet Controller for the Pi, is missing from the new board. In its place is the VLI VL805 which provides a USB 3.0 Hub over a PCI Express bus.
Using the PCI Express bus provided by the new BCM2711 means that not only do we now have USB 3.0 capability, but the Gigabit Ethernet than was previous provided via the USB bus and the LAN7515 chip—which had a maximum throughput limited to around 300Mbps—is now provided using the Broadcom BCM54213PE on a separate bus to the USB traffic.
That means that, rather than being throttled as we saw with the Raspberry Pi 3, Model B+, the new Raspberry Pi 4 has ‘real’ Gigabit Ethernet.
Yes. You heard that right. The new Raspberry Pi board has both ‘real’ Gigabit Ethernet and two USB 3.0 ports as well as a couple more ‘legacy’ USB 2 ports.
Wireless support is provided in an RF shielded module by the same Cypress CYW43455 chip as we saw on the Raspberry Pi 3, Model B+. Offering dual-band 2.4GHz and 5GHz IEEE 802.11.b/g/n/ac wireless networking, as well as Bluetooth 5.0 and Bluetooth LE.
For completeness the final big bit of silicon—located just to the right of the main processor package—is the LPDDR4 SDRAM for the board which comes in the shape of a Micron FBGA-packaged chip, and this is where another big difference from previous Raspberry Pi models shows its head.
Unlike any previous board, the new Raspberry Pi 4 is available in three different models, each offering a different memory options. The new board can come with either 1GB, 2GB or 4GB of RAM.
The pre-release board I had for review ahead of the launch had 4GB.
Powering the Board
Another big difference is the power jack, gone is the micro-USB jack from previous models, and in its place is a USB-C jack. It’s an understandable change. The tolerances on the power supply for the Raspberry Pi 3, Model B+, were already pretty thin, and the new board can require up to 3 Amps, that’s not something that the previous micro-USB supply could provide.
The board can also be powered via 5V DC supply using the GPIO headers, and like the Raspberry Pi 3, Model B+, before it the new Raspberry Pi 4 can also be powered by Power over Ethernet (PoE) using the official PoE HAT that was released alongside the previous model last year.
A New Official Power Supply
With the switch from micro USB to USB C comes a new official power supply. However while USB C chargers typically retail for anywhere between $10 to $60, the new 15W official supply is priced at just $8, which is sort of market breaking. Because plenty of people that have never even heard of Raspberry Pi will buy it at that price point. Also, like the original micro USB supply, the new USB C power supply has been designed as a power supply, not a charger.
Yes, that makes a big difference.
Like most single-board computers and micro-controllers the Raspberry Pi takes a nominal 5V input supply. However in reality the voltage will bounce around somewhat due to demands made by the board, and most USB supplies actually sit at around +5.1 to +5.2V. So when doing rough calculations to get the power (in Watts) I’d normally take a the voltage of a USB supply to be +5.15V as a good supply will usually try and maintain the supplied voltage around this figure despite rapid fluctuations in current draw.
Those fluctuations in demand is something that happens a lot with when you’re using peripherals with the Raspberry Pi and often cause brown outs, and they are something that a lot of USB chargers — designed to provide consistent current for charging cellphones — usually don’t cope with all that well.
“We’re conscious that by moving to USB-C for power we’re asking people to invest in a new PSU, and that right now even middling-quality USB-C supplies tend to retail for over $10. We’re putting two products in the market to address this. The first is an $8 AC adapter, which we’ve carefully specified to be a good match for our needs. The second is a $1 shim which converts from USB micro-B to USB-C: people who own the official Raspberry Pi 3 PSU, or an equivalent third-party unit, and who don’t want to be able to draw the full 1.2A out of our downstream USB ports, can use this to get started quickly and cheaply.” — Eben Upton, Founder, Raspberry Pi Foundation
However don’t worry if you have a more than a few of the original official micro-USB chargers lying around. Because you can also pick up a micro-USB to USB-C convertor for the original charger, for just $1. I wouldn’t attempt to use it with most micro USB chargers, but the original official supply is pretty robust.
The Board and the Case
If you look carefully at the board there are a few changes, it might take you a few moments to notice, you might not even have noticed yet, but the positions of the Ethernet and USB ports have been swapped left to right. There’s also slightly more overhang on those connectors, and combined with the other changes, that means existing cases won’t fit the new board.
Also changed is the video ports. Gone is the full sized HDMI jack offered by previous generations of Raspberry Pi boards. However in its place are two micro-HDMI ports, and yes that means the new Raspberry Pi 4 has dual monitor support—supporting one 4K screen at 60fps, or two 4K screens at 30fps.
Alongside the two micro-HDMI ports is a 4-pole stereo output, and composite video, jack. The board also has OpenGL ES 1.1, 2.0, and 3.0 graphics support, and supports H.265 decode (4kp60), H.264 decode (1080p60), and H.264 encode (1080p30). Also, and for the first time, the GPU drivers shipping with the board are open source.
Alongside the big changes are some things haven’t changed. Storage is still provided by a micro SD Card, with the connector in the familiar place on the underside of the board. While the new Raspberry Pi 4 still supports an MIPI DSI display port connector, and a MIPI CSI camera connector, along with the now standard 40-pin GPIO header.
However there are some changes for the 40-pin header, although it is still backwards compatible the header block of the new Raspberry Pi has an support for an additional 4× UART, 4× SPI, and 4× I2C connectors.
The Operating System
One big change that isn’t immediately evident on the surface is the operating system. The Foundation’s Raspbian distribution is Debian-based, and with the upcoming release of Debian Buster and support for the new hardware found on the Raspberry Pi 4 being easier under the new release, the Raspberry Pi 4 ships with Raspbian Buster. So while it’s still running Raspbian, there are significant changes so don’t expect everything to be the same, or work out of the box. There will inevitably be some teething troubles as people fix, patch, and port things to Buster after today’s release.
Heating and Cooling
While we saw some initial reports of heat issues after the release of the original Raspberry Pi 3 board in 2017, the Raspberry Pi has always been fairly thermally stable. While there were plenty of heat sinks and fans available, they weren’t really needed unless you intended to run the board flat out inside a confining case, and under normal operating conditions this is still probably going to be the case for the Raspberry Pi 4.
I ran the board for several hours with several 4K video streams playing, while simultaneously browsing the web or playing video games simulating ‘normal’ desktop usage. the CPU temperatures rose and settled around 68°C. This is well below the thermal throttling limit of 80°C, and unlike previous models the Raspberry Pi 4 has no incremental thermal throttling. This means that for most use cases cooling is needed.
However in some extreme cases some measure of passive, or active, cooling will be needed. We saw evidence of this during our benchmarking.
During extended testing using the machine learning frameworks TensorFlow and AI2GO we observed temperatures well above the thermal throttling threshold, around 84°C. However the addition of a small fan, driven from the +5V pin on the GPIO headers, was sufficient to bring the CPU temperature down to 45°C and keep it stable at that point during our testing.
One More Thing…
Finally then, the new Raspberry Pi will be available as part of a Desktop Kit.
“The Desktop Kit, which will retail for $120+tax, is intended as a complete no-compromises package of components, giving you everything apart from the monitor that you need to use the 4GB Raspberry Pi as a desktop computer.” — Eben Upton, Founder, Raspberry Pi Foundation
The desktop kit includes the 4GB version of the new Raspberry Pi 4 along with the official keyboard, mouse, case, and the new USB C power supply. Also included is a getting started guide updated for the new board a micro-HDMI cable, and an SD Card with a pre-burned Raspbian installation.
The new Raspberry Pi 4, Model B, is available in three versions. The lowest priced version has the same 1GB of memory as all the previous models and shares the same $35 price tag. However it is also available is a 2GB model priced at $45, and a high end model with 4GB of RAM priced at $55. But there aren’t any other differences between the three models except the amount of RAM on the board.
Up until now competitors have managed to compete, mostly poorly, with the Raspberry Pi by adding extra memory, or Gigabit Ethernet, or USB 3. All of which the Raspberry Pi now has, so it’s going to be rather interesting to see how the next ‘Raspberry Pi killer’ is pitched, especially since most boards I’ve seen just don’t even try and compete on price.
The new Raspberry Pi 4 is available today; however if instead of placing an order for one, you really want one in your hands today, there is one spot you can do that. The Raspberry Pi store in Cambridge has them in stock.
So if you’re in Cambridge, or at least nearby in London, and you think you can get away with it, maybe take the afternoon off and head to the Grand Arcade in the centre of Cambridge. Pick up one of the first Raspberry Pi 4’s, and tweet me. Because I’m fascinated to see if the launch is going to cause a queue.