Make water cooling great again

Although I'm sure there are one-offs, the last and most powerful Power architecture workstation to ship liquid-cooled from the factory was the Power Mac Quad G5. It's nice and quiet compared to the air-cooled G5s and allowed Apple to get that extra edge out of the PowerPC 970, though I did have to replace my cooling system a few years ago and you always have to watch for leaks. While I don't find this dual-8 Raptor Talos II to be particularly loud with the stock HSFs, it might be nice to get my 4-core HTPC Blackbird a little quieter when I'm watching a movie and I think that would be worth having to do a little service on it now and then.

While Raptor has no known plans to ship liquid-cooled machines, Vikings has your back (note that their store is down as of this writing for "spring cleaning"). The key with the IBM HSFs is that they get good, high-pressure contact between the heat spreader and the fan heatsink such that you can run 4 and 8-core parts without thermal compound or indium pads. While the custom mount Vikings developed doesn't achieve that level presently, with MX5 thermal compound they demonstrated over a 10 degree C reduction in core temperatures under load compared to the stock HSFs on a single 22-core POWER9. The custom CPU fitting then connects to an off-the-shelf Laing DC pump and a 120mm radiator.

There are of course problems to be solved before this becomes a workable product even though this prototype is very promising. Vikings is still trying to figure out how much pressure should be applied by the CPU clamp; while the use of thermal compound allows a bit of wiggle room here, clamp down too much and you'll crack the chip but too little and it won't cool. (The IBM HSFs are very user-friendly in this regard: turn until it stops.) There are also concerns the compression fittings may be too tight and a manufacturing issue with the mechanism's upper plate. For my money, since I already have one expensive liquid-cooled computer under this desk, I'd also want easy serviceability to drain fluids and replace tubing, and I'd want high quality components and fittings to reduce evaporative loss and the chance of any dreaded leaks. Like anything else, pay now for quality or pay later for damage.

Still, additional cooling options would be great for getting OpenPOWER machines in more places they haven't been before, and while the little 4-cores run very cool with just passive heatsinks, running dual-8s or higher core counts might really benefit from a liquid cooling system (especially you nuts out there trying to cram 18-core parts into Blackbirds). No ETA on a saleable product yet but I'm looking forward to seeing it develop.


  1. This is awesome. I've always wanted to see more cooling options on the OpenPower boxes.

  2. I know this isn't germane to the topic, but it looks like some PPC64 reinvigoration is happening. Where should I donate a G4 PowerBook to that end?

    1. I'm sure the kind thought is appreciated, but unfortunately the G4 PowerBook is 32-bit ...

    2. Gah, it's been a long day - meant PPC32...

  3. WAIT. They did that with a *single* 120mm rad????? OMGGGGG. You could probably see a whole 10c drop from there on a bigger, thicker radiator.


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