Desktop PC Component Advantage: Sustained Performance

A few weeks ago I decommissioned Luggable PC Mark II and the components were installed into a standard desktop tower case. Heeding Hackaday’s call for donating computing power to Folding@Home, I enlisted my machines into the effort and set up my own little folding farm. This activity highlighted a big difference between desktop and laptop components: their ability to sustain peak performance.

My direct comparison is between my ex-Luggable PC Mark II and the Dell laptop that replaced it for my mobile computing needs. Working all out folding proteins, both of those computers heated up. Cooling fans of my ex-Luggable sped up to a mild whir, the volume and pitch of the sound roughly analogous to my microwave oven. The laptop fans, however, spun up to a piercing screech whose volume and pitch is roughly analogous to a handheld vacuum cleaner. The resemblance is probably not a coincidence, as both move a lot of air through a small space.

The reasoning is quite obvious when we compare the cooling solution of a desktop Intel processor against one for a mobile Intel processor. (Since my active-duty machines are busy working, I pulled out some old dead parts for the comparison picture above.) Laptop engineers are very clever with their use of heat pipes and other tricks of heat management, but at the end of the day we’re dealing with the laws of physics. We need surface area to transfer heat to air, and a desktop processor HSF (heat sink + fan) has tremendously more of it. When workload is light, laptops keep their fans off for silent operation whereas desktop fans tend to run even when lightly loaded. However, when the going gets rough, the smaller physical volume and surface area of laptop cooling solutions struggle.

This is also the reason why different laptop computers with nearly identical technical specifications can perform wildly differently. When I bought my Inspiron 7577, I noticed that there was a close relative in Dell’s Alienware line that has the same CPU and GPU. I decided against it as it cost a lot more money. Some of that is branding, I’m sure, but I expect part of it goes to more effective heat removal designs.

Since I didn’t buy the Alienware, I will never know if it would have been quieter running Folding@Home. To the credit of this Inspiron, that noisy cooling did keep its i5-7300HQ CPU at a consistent 3.08GHz with all four cores running full tilt. I had expected thermal throttling to force the CPU to drop to a lower speed, as is typical of laptops, so the fact this machine can sustain such performance was a pleasant surprise. I appreciate the capability but that noise got to be too much… when I’m working on my computer I need to be able to hear myself think! So while the ex-Luggable continued to crunch through protein simulations, the 7577 had to drop out. I switched my laptop to the “Finish” option where it completed the given work unit overnight (when I’m not sitting next to it) and fetched no more work.

This experience taught me one point in favor of a potential future Luggable PC Mark III: the ability to run high performance workloads on a sustained basis without punishing hearing of everyone nearby. But this doesn’t mean mobile oriented processors are hopeless. They are actually a lot of fun to hack, especially if an old retired laptop doesn’t need to be mobile anymore.

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