Intel Skylake bug causes PCs to freeze during complex workloads
Bug discovered while using Prime95 to find Mersenne primes.

by Mark Walton (UK) - Jan 11, 2016
arstechnica.com



Intel has confirmed that its Skylake processors suffer from a bug that can cause a system to freeze when performing complex workloads. Discovered by mathematicians at the Great Internet Mersenne Prime Search (GIMPS), the bug occurs when using the GIMPS Prime95 application to find Mersenne primes.

"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 behaviour."

Intel has developed a fix, and is working with hardware partners to distribute it via a BIOS update.

No reason has been given as to why the bug occurs, but it's confirmed to affect both Linux and Windows-based systems. Prime95, which has historically been used to benchmark and stress-test computers, uses Fast Fourier Transforms to multiply extremely large numbers. A particular exponent size, 14,942,209, has been found to cause the system crashes.

While the bug was discovered using Prime95, it could affect other industries that rely on complex computational workloads, such as scientific and financial institutions. GIMPS noted that its Prime95 software "works perfectly normal" on all other Intel processors of past generations.

While this particular bug can be fixed via a BIOS update, we are reminded of another famous bug that plagued Intel's original Pentium processor that couldn't be so easily rectified. The Pentium FDIV bug—discovered by Thomas Nicely, a professor of mathematics, on October 19, 1994—was a floating-point divide problem caused by a circuit design error.

While the flaw would rarely have been encountered by average users, extensive media coverage ultimately led to Intel recalling the defective processors.

Mostly recently, Intel's Haswell and early Broadwell processors suffered from a TSX ( Transactional Synchronization Extensions) bug. Rather than recall the parts, Intel disabled the TSX instructions via a microcode update delivered via new motherboard firmware.