Still, it's hard to believe the fault lies completely with the speed of the M.2 inside the Spectre x360. My gut still says the problem might be the culprit I often see: CPU throttling from heat.
I subjected the Spectre x360 to several runs of Futuremark's 3DMark Sky Diver test. Rather than just run the overall benchmark, I left on the "demo" mode, which includes several minutes of "cool" graphics sequences. Most reviewers, including myself, usually uncheck this mode to save time. The result I saw for the Spectre x360 when I first tested it some weeks ago, for example, was 2,751--a little faster than the Dell XPS 13 2015 QHD+, which scored 2,650.
I know from previous reviews, however, that leaving the demo mode on heats up some laptops with borderline thermal solutions, or those that choose temperature or acoustics over performance, only to see their scores fall off. The first run of 3DMark on the Spectre x360 gave me 2,385. The second run: 2,327, and the third run hit 2,215. I then let the Spectre x360 sit for five minutes to cool down. I ran the same test but with the demo mode turned off. The result? 2,721.
Surely we'd see this with any Ultrabook pushed this hard, right? As a control, I broke out Dell's XPS 13 2015 QHD+ model and ran 3DMark three times with the demo mode on, barely giving it time to recover between runs. The first score: 2,707. The second: 2,708, and the final run: 2,715. I then let it sit for five minutes and ran it again with the demo mode switched off: 2,715.
This is a very roundabout way of saying the Spectre x360 exhibits some thermal throttling. Perhaps there's also some SSD sensitivity in Handbrake as HP says, but that's about a 14- to 15-percent difference in performance I'm seeing from heating up the CPU in 3DMark, and that does not touch the SSD.
This isn't a gaming test necessarily, it's a thermal load test. Any lengthy CPU or GPU load on the Spectre x360 would likely see performance fall off. How far down it'll throttle I didn't test, but Handbrake saw about an 18-percent difference between the XPS 13 and Spectre x360 during its 2-hour-plus encode.
To be fair, the XPS 13 is slightly thicker than the Spectre x360, and its fan curve is borderline obnoxious at times with its original BIOS. But it's pretty obvious there's no throttling issue on the XPS 13--Dell simply chose flat-out performance all the time. When you also consider that the XPS 13 is smaller, that puts it more in perspective.
Keep in mind, laptop designs are all about balancing fan noise, shell thermals, and performance. Like the old saying goes, you can't have it all, especially in a thin laptop.
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