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How to test your PC for the Skylake bug

Gordon Mah Ung | Jan. 12, 2016
Intel confirms there's a bug that could crash Skylake CPUs, under specific and somewhat uncommon circumstances.

skylake cpu
Credit: Gordon Mah Ung

Intel has confirmed a bug in some Skylake CPUs could cause them to lock up under “complex workload conditions” but noted that a fix is on the way.

The bug initially was reported only with the Core i7-6700K desktop CPU with Hyper-Threading enabled, but Intel’s confirmation seems to indicates it impacts more CPUs in the lineup.

In a post on Intel’s forums, an Intel community manager wrote: “Intel has identified an issue that potentially affects the 6th Gen Intel Core family of products. This issue only occurs under certain complex workload conditions, like those that may be encountered when running applications like Prime95. In those cases, the processor may hang or cause unpredictable system behavior. Intel has identified and released a fix and is working with external business partners to get the fix deployed through BIOS.”

The bug has apparently been stewing for weeks on forums at and then which created the software, Prime95, that is used to induce the bug. Prime95 is used to find prime numbers and is also very popular with performance and the overclocking community as a stress and performance test.

Intel said some Skylake chips might lock up under a “complex workload conditions” but most people can relax on this one. Credit: Gordon Mah Ung

Besides the community post, Intel also confirmed to PCWorld the existence of the bug but placed an emphasis on the word “might” because there’s no guarantee you’ll hit the bug.

“Under some complex workload conditions, like those encountered when running applications such as Prime95, the processor may hang or cause unpredictable system behavior. Intel has released a fix that resolves the issue and we are working with external business partners to deploy this fix through BIOS updates,” an Intel official told PCWorld.

This may seem like Intel's sugar-coating it, but the bug is truly sporadic. Some people have run into it, while others can’t reproduce it. The hang sometimes occurs after minutes, sometimes hours, and others never experience the lockup.

In my own testing, I used a Skylake-based laptop with a quad-core Core i7-6820HK and didn’t experience the hangup in a few hours of testing. Many of the people who've reported hitting the bug are doing so with the desktop Core i7-6700K chip, though.

Why this matters: In the grand scheme of CPU “errata” or bugs, this one is fairly esoteric and really not worthy of being mentioned in the same paragraph as Intel’s infamous 1994 FDIV bug. The FDIV bug would manifest itself in Microsoft Excel spreadsheets and was serious enough that Intel recalled the CPUs to the tune of millions of dollars. The bigger bummer for PC users was when Intel couldn't resolve a bug in its new TSX instructions, so it simply switched it off for many people. The Skylake bug can apparently be patched with a microcode fix.


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