Skylake (microarchitecture)

Lore & Background

Skylake's development was primarily undertaken by Intel Israel at its engineering research center in Haifa, Israel. The final design was largely an evolution of Haswell, with minor improvements to performance and several power-saving features. A major priority was designing a microarchitecture for envelopes as low as 4.5W for tablets and notebooks, as well as higher-power desktop computers and servers. In September 2014, Intel announced the Skylake microarchitecture at the Intel Developer Forum in San Francisco, with volume shipments scheduled for the second half of 2015. An initial batch of CPU models (i5-6600K and i7-6700K) was announced for immediate availability during Gamescom on August 5, 2015, unusually soon after the release of its predecessor Broadwell, which had suffered from launch delays. Intel acknowledged that moving from 22 nm to 14 nm had been its most difficult process to develop, causing Broadwell's planned launch to slip, but 14 nm production was back on track as of Q3 2014. Industry observers had believed Broadwell's issues would cause Skylake to slip to 2016, but Intel brought forward Skylake's release and shortened Broadwell's release cycle instead.

Skylake is available in five variants: S (SKL-S), X (SKL-X), H (SKL-H), U (SKL-U), and Y (SKL-Y). The H, U, and Y variants are manufactured in ball grid array (BGA) packaging, while S and X variants use land grid array (LGA) packaging with new sockets LGA 1151 and LGA 2066. Major changes from Haswell include the removal of the fully integrated voltage regulator (FIVR) and the replacement of DMI 2.0 with DMI 3.0, allowing speeds up to 8 GT/s. Skylake remains backward compatible with both DDR3 and DDR4 memory.

Reader's Guide

Skylake's significance lies in its role as a major tock in Intel's tick-tock model, delivering a microarchitecture redesign that improved CPU and GPU performance while reducing power consumption. It was the last Intel platform to officially support Windows 7 and Windows 8.1, with Microsoft initially planning to end support in July 2017, later revising the cutoff to July 2018, and finally stating it would fully support those OSes through the end of their lifecycles. For Windows 11, only high-end Skylake-X processors are officially listed as compatible; other Skylake processors are not officially supported due to security concerns, though manual upgrades are possible with TPM 2.0. Skylake also saw controversy over overclocking: Intel officially supported overclocking only on K and X variants, but motherboard vendors like ASRock allowed base clock overclocking of non-K chips via beta UEFI firmware updates, which caused issues such as disabled C-states, disabled Turbo Boost, disabled integrated graphics, poor AVX2 performance, and incorrect temperature readings. Intel later issued a microcode update removing this function, and ASRock began selling motherboards using an external clock generator. Skylake's UEFI firmware implementations mostly no longer support Windows XP and Windows Server 2003 due to incompatible ACPI versions.

Did You Know?

• Overclocking of non-K Skylake processors via base clock modification caused C-states, Turbo Boost, and integrated graphics to be disabled.
• Intel officially declared end of life for Skylake LGA 1151 CPUs (except i3-6100, i5-6500, and Xeon E3 v5) on March 4, 2019.