Adventures In Overclocking: Which Raspberry Pi 4 Flavor Is Fastest?

There are three different versions of the Raspberry Pi 4 out on the market right now: the “normal” Pi 4 Model B, the Compute Module 4, and the just-released Raspberry Pi 400 computer-in-a-keyboard. They’re all riffing on the same tune, but there are enough differences among them that you might be richer for the choice.

The Pi 4B is easiest to integrate into projects, the CM4 is easiest to break out all the system’s features if you’re designing your own PCB, and the Pi 400 is seemingly aimed at the consumer market, but it has a dark secret: it’s an overclocking monster capable of running full-out at 2.15 GHz indefinitely in its stock configuration.

In retrospect, there were hints dropped everywhere. The system-on-a-chip that runs the show on the Model B is a Broadcom 2711ZPKFSB06B0T, while the SOC on the CM4 and Pi 400 is a 2711ZPKFSB06C0T. If you squint just right, you can make out the revision change from “B” to “C”. And in the CM4 datasheet, there’s a throwaway sentence about it running more efficiently than the Model B. And when I looked inside the Pi 400, there was this giant aluminum heat spreader attached to the SOC, presumably to keep it from overheating within the tight keyboard case. But there was one more clue: the Pi 400 comes clocked by default at 1.8 GHz, instead of 1.5 GHz for the other two, which are sold without a heat-sink.

Can the CM4 keep up with the Pi 400 with a little added aluminum? Will the newer siblings leave the Pi 4 Model B in the dust? Time to play a little overclocking!

Raspberry Overdrive

Overclocking a Raspberry Pi is basically painless. In most cases, it’s as simple as editing your /boot/config.txt file and typing in the desired maximum speed and CPU core voltage. If it doesn’t boot, you pick a lower CPU speed until you get something that works. But that doesn’t mean that you’re going to get the full performance bump — the main CPUs run alongside, or maybe underneath, the GPUs which run the ThreadX RTOS, and throttle the main CPUs when they get hot.

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Die Lapping For Better CPU Performance

CPUs generate their heat in the silicon die that does all those wonderful calculations which make our computers work. But silicon conducts heat fairly poorly, so the thinner your CPU die, the better it will conduct heat out to the heatsink. This theoretically promises better cooling and thus more scope for performance. Thus, it follows that some overclockers have taken to lapping down their CPU dies to try and make a performance gain.

It’s not a simple process, as the team at [Linus Tech Tips] found out. First, the CPU must be decapped, which on the Intel chip in question requires heating to release the intermediate heat spreader. A special jig is also required to do the job accurately. Once the bare CPU is cleaned of all residual glue and heat compounds, it can then be delicately lapped with a second jig designed to avoid over-sanding the CPU.

After much delicate disassembly, lapping, and reassembly, the CPU appears to drop 3-4 degrees C in benchmarks. In overclocking terms, that’s not a whole lot. While the process is risky and complicated for little gain, the underlying premise has merit – Intel thinned things out in later chips to make minor gains themselves. Video after the break.

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Overclocking In An SNES Emulator

The bsnes emulator has a new overclocking mode to eliminate slowdowns in SNES games while keeping the gameplay speed accurate. We’re emulating old SNES hardware on modern machines that are vastly more powerful. Eliminating slowdowns should be trivial, right? For an emulator such as bsnes, which is written to achieve essentially pixel-perfect accuracy when emulating, the problem is decidedly non-trivial. Stick around to learn why.

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Oil-Immersed Raspberry Pi Keeps Its Cool Under Heavy Loads

As a general rule, liquids and electronics don’t mix. One liquid bucks that trend, though, and can contribute greatly to the longevity of certain circuits: oil. Dielectric oil cools and insulates everything from the big mains transformers on the pole to switchgear in the substation. But what about oil for smaller circuits?

[Lord_of_Bone] was curious to see if an oil-cooled Raspberry Pi is possible, and the short answer is: for the most part, yes. The experimental setup seen in the video below is somewhat crude — just a Pi running Quake 3 for an hour to really run up the CPU temperature, which is monitored remotely. With or without heatsinks mounted, in free air the Pi ranges from about 50°C at idle to almost 70°C under load, which is pretty darn hot. Dunking the Pi in a bath of plain vegetable oil, which he admits was a poor choice, changes those numbers dramatically: 37°C at idle and an only warmish 48°C after an hour of gaming. He also tested the Pi post-cleaning, which is where he hit a minor hiccup. The clean machine started fine but suffered from a series of reboots shortly thereafter. Twelve hours later the Pi was fine, though, so he figures a few stray drops of water that hadn’t yet evaporated were to blame.

Is oil immersion a practical way to cool a Pi? Probably not. It doesn’t mean people haven’t tried it before, of course, but we applaud the effort and the careful experimentation.

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Overclock Your Raspberry Pi The Right Way

The Raspberry Pi came upon us as an educational platform. A credit card sized computer capable of running Linux from a micro SD card, the Raspberry Pi has proven useful for far more than just education. It has made its way into every nook and cranny of the hacker world. There are some cases, however, where it might be a bit slow or seem a bit under powered. One way of speeding the Raspi up is to overclock it.

[Dmitry] has written up an excellent overclocking guide based upon Eltech’s write up on the subject. He takes it a bit further and applies the algorithm to both Raspi 2 and Raspi 3. You’ll need a beefier power supply, some heat sinks and fans – all stuff you probably have lying around on your workbench. Now there’s no excuse stopping you from ratcheting up the MHz and pushing your Pi to the limit!

We’ve seen several guides to overclocking the Raspi here on Hackaday, including the current record holder. Be sure to check out [dmitry’s] IO page for the overclocking details, and let us know of any new uses you’ve found by overclocking your Raspi in the comment below.

Liquid Cooling Overclocked Raspberry Pi With Style

[HydroGraphix HeadQuarters] has earned his name with this one. While he is using mineral oil instead of hydro, he’s certainly done a nice job with the graphics of it. The ‘it’ in questions is an overclocked Raspberry Pi 3 in a transparent container filled with mineral oil, and with a circulating fan.

He’s had no problem running the Pi at 1.45 GHz while running a Nintendo 64 emulator, getting between 40 °C and 50 °C. The circulating fan is a five volt computer USB fan. It’s hard to tell if the oil is actually moving, but we’re pretty sure we see some doing so near the end of the video below the break.

Mineral oil is not electrically conductive, and is often used to prevent arcing between components on high voltage multiplier boards, but those components are always soldered together. If you’ve ever worked with mineral oil, you know that it creeps into every nook and cranny, making us wonder if it might work its way between some of the (non-soldered) contacts in the various USB connectors on this Raspberry Pi. Probably not, but those of us with experience with it can attest to it’s insidiousness.

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Pi Keeps Cool At 1.5 GHz

Hackers have a long history of overclocking CPUs ranging from desktop computers to Arduinos. [Jacken] wanted a little more oomph for his Pi Zero-Raspberry Pi-based media center, so he naturally wanted to boost the clock frequency. Like most overclocking though, the biggest limit is how much heat you can dump off the chip.

[Jacken] removed the normal heat sink and built a new one out of inexpensive copper shim, thermal compound, and super glue. The result isn’t very pretty, but it does let him run the Zero Pi at 1.5 GHz reliably. The heat sink is very low profile and doesn’t interfere with plugging other things into the board. Naturally, your results may vary on clock frequency and stability.

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