Skylake is the codename used by Intel for a processor microarchitecture which was launched in August 2015 succeeding the Broadwell microarchitecture. Skylake is a microarchitecture redesign using the same 14 nm manufacturing process technology as its predecessor Broadwell, serving as a "tock" in Intel's "tick-tock" manufacturing and design model. According to Intel, the redesign brings greater CPU and GPU performance and reduced power consumption. It has been succeeded by Kaby Lake.
Skylake is the last Intel platform on which Windows earlier than Windows 10 will be officially supported by Microsoft, although enthusiast-created modifications exist which allow Windows 8.1 and earlier to continue to receive updates on later platforms.
Some of the processors based on the Broadwell microarchitecture are marketed as "6th-generation Core".
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Development history
Skylake's development, as with processors such as Banias, Dothan, Conroe, Sandy Bridge and Ivy Bridge, was primarily undertaken by Intel Israel at its engineering research center in Haifa, Israel. The Haifa development team worked on the project for four years, and faced many challenges: "But by re-writing the microarchitecture and developing new concepts such as the Speed Shift Technology, we created a processor for 4.5 W to 45 W mobile devices, and up to 91 W for desktop devices." The Skylake processors will be used to power a wide range of devices, from smartphones and tablets, all the way to desktops. "Because of Skylake's features, companies will be able to release laptop PCs that are half as thick and half as heavy as those from five years ago," according to Intel.
In September 2014, Intel announced the Skylake microarchitecture at the Intel Developer Forum in San Francisco, and that volume shipments of Skylake CPUs were scheduled for the second half of 2015. Also, the Skylake development platform was announced to be available in Q1 2015. During the announcement, Intel also demonstrated two computers with desktop and mobile Skylake prototypes: the first was a desktop testbed system, running the latest version of 3DMark, while the second computer was a fully functional laptop, playing 4K video.
An initial batch of Skylake CPU models (6600K and 6700K) was announced for immediate availability during the Gamescom on August 5, 2015, unusually soon after the release of its predecessor, Broadwell, which had suffered from launch delays. Intel acknowledged in 2014 that moving from 22 nm (Haswell) to 14 nm (Broadwell) had been its most difficult process to develop yet, causing Broadwell's planned launch to slip by several months; yet, the 14 nm production was back on track and in full production as of Q3 2014. Industry observers had initially believed that the issues impacting Broadwell would also cause Skylake to slip to 2016, but Intel was able to bring forward Skylake's release and shorten Broadwell's release cycle instead. As a result, the Broadwell architecture had an unusually short run.
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Overclocking of unsupported processors
Officially Intel supported overclocking of only the "K" and "X" versions of Skylake processors. However, it was later discovered that other "non-K" chips could be overclocked by modifying the base clock value - a process made feasible by the base clock only applying to the CPU, RAM, and integrated graphics on Skylake. Through beta UEFI firmware updates, some motherboard vendors, such as ASRock (which prominently promoted it under the name "Sky OC") allowed the base clock to be modified in this manner.
In February 2016, however, an ASRock firmware update removed the feature. On February 9, 2016, Intel announced that it would no longer allow such overclocking of non-K processors, and that it had issued a CPU microcode update which removes the function. In April 2016 ASRock started selling motherboards which allow overclocking of unsupported CPUs using an external clock generator.
Operating system support
In January 2016, Microsoft announced that it would end support of Windows 7 and Windows 8.1 on Skylake processors effective July 17, 2017; after this date, only the "most critical" updates for the two operating systems would be released for Skylake users if they have been judged not to affect the reliability of the OS on older hardware, and Windows 10 would be the only Microsoft Windows platform officially supported on Skylake, as well as all future Intel CPU microarchitectures beginning with Skylake's successor Kaby Lake. Terry Myerson stated that Microsoft had to make a "large investment" in order to reliably support Skylake on older versions of Windows, and that future generations of processors would require further investments. Microsoft also stated that due to the age of the platform, it would be "challenging" for newer hardware, firmware, and device driver combinations to properly run under Windows 7.
On March 18, 2016, in response to criticism over the move, primarily from enterprise customers, Microsoft announced revisions to the support policy, changing the cutoff for support and non-critical updates to July 17, 2018 and stating that Skylake users would receive all critical security updates for Windows 7 and 8.1 through the end of extended support. In August 2016, citing a "strong partnership with our OEM partners and Intel", Microsoft stated that it would continue to fully support 7 and 8.1 on Skylake through the end of their respective lifecycles. In addition, an enthusiast-created modification was released that disabled the Windows Update check and allowed Windows 8.1 and earlier to continue to be updated on this and later platforms.
As of Linux kernel 4.10, Skylake mobile power management is in reasonably good shape with most Package C states supported seeing some use. If this is not the case, then the cause is likely bugs in the system firmware of the particular computer, which might be resolved by updating the BIOS. The user can easily optimize power management beyond the Linux default settings with the powertop utility and its systemd service, which will start up with the computer and auto-tune various settings to reduce power usage. Linux 4.11 enables Frame-Buffer Compression for the integrated graphics chipset by default, which lowers power consumption. Battery runtime should be similar to Windows 10 and possibly better, but further improvements can still be made.
As of OpenBSD version 6.1, Skylake is not supported, missing support for video acceleration amongst other things. In development versions leading up to version 6.2, at least initial support for Skylake-specific features is present.
Features
Like its predecessor, Broadwell, Skylake is available in five variants, identified by the suffixes "S" (SKL-S), "X" (SKL-X), "H" (SKL-H), "U" (SKL-U), and "Y" (SKL-Y). SKL-S and SKL-X contains an overclockable "K" and "X" variant with unlocked multipliers. The H, U and Y variants are manufactured in ball grid array (BGA) packaging, while the S variant is manufactured in land grid array (LGA) packaging using a new socket, LGA 1151 (LGA 2066 for Skylake X). Skylake is used in conjunction with Intel 100 Series chipsets, also known as Sunrise Point.
The major changes between the Haswell and Skylake architectures include the removal of the fully integrated voltage regulator (FIVR) introduced with Haswell. On the variants that will use a discrete Platform Controller Hub (PCH), Direct Media Interface (DMI) 2.0 is replaced by DMI 3.0, which allows speeds of up to 8 GT/s.
Skylake's U and Y variants support one DIMM slot per channel, while H and S variants support two DIMM slots per channel. Skylake's launch and sales lifespan occur at the same time as the ongoing SDRAM market transition, with DDR3 SDRAM memory gradually being replaced by DDR4 memory. Rather than working exclusively with DDR4, the Skylake microarchitecture remains backward compatible by interoperating with both types of memory. Accompanying the microarchitecture's support for both memory standards, a new SO-DIMM type capable of carrying either DDR3 or DDR4 memory chips, called UniDIMM, was also announced.
Skylake's few P variants have a reduced on-die graphics unit (12 exections units enabled instead of 24 execution units) over their direct counterparts, see the table below. In contrast, with Ivy Bridge CPUs the P suffix was used for CPUs with completely disabled on-die video chipset.
Other enhancements include Thunderbolt 3.0, SATA Express, Iris Pro graphics with Direct3D feature level 12_1 with up to 128 MB of L4 eDRAM cache on certain SKUs. The Skylake line of processors retires VGA support, while supporting up to five monitors connected via HDMI 1.4, DisplayPort 1.2 or Embedded DisplayPort (eDP) interfaces. HDMI 2.0 (4K@60 Hz) is only supported on motherboards equipped with Intel's Alpine Ridge Thunderbolt controller.
The Skylake instruction set changes include Intel MPX (Memory Protection Extensions) and Intel SGX (Software Guard Extensions). Future Xeon variants will also have Advanced Vector Extensions 3.2 ("AVX-512F").
Skylake-based laptops may use wireless technology called Rezence for charging, and other wireless technologies for communication with peripherals. Many major PC vendors have agreed to use this technology in Skylake-based laptops, which should be released by the end of 2015.
The integrated GPU of Skylake's S variant supports on Windows DirectX 12 Feature Level 12_1, OpenGL 4.5 with latest Windows 10 driver update (OpenGL 4.5 on Linux) and OpenCL 2.0 standards, as well as some modern hardware video encoding/decoding formats such as VP9 (GPU accelerated decode only), VP8 and HEVC (hardware accelerated 8-bit encode/decode and GPU accelerated 10-bit decode).
Intel also released unlocked (capable of overclocking) mobile Skylake CPUs.
Unlike previous generations, Skylake-based Xeon E3 no longer works with a desktop chipset that supports the same socket, and requires either the C232 or the C236 chipset to operate.
Known issues
Skylake has a critical flaw where some short loops may cause unpredictable system behavior on CPUs with hyperthreading. A microcode update was issued to fix the issue.
Architecture
- Improved front-end, deeper out-of-order buffers, improved execution units, more execution units (third vector integer ALU(VALU)) for five ALUs in total, more load/store bandwidth, improved hyper-threading (wider retirement), speedup of AES-GCM and AES-CBC by 17% and 33% accordingly.
- 14 nm manufacturing process
- LGA 1151 socket for mainstream desktop processors and LGA 2066 socket for enthusiast gaming/workstation "X-Series" processors
- 100 Series chipset (Sunrise Point)
- "X" Series uses X299 series chipset
- Thermal design power (TDP) up to 95 W (LGA 1151); up to 160 W (LGA 2066)
- Support for both DDR3L SDRAM and DDR4 SDRAM in mainstream variants, using custom UniDIMM SO-DIMM form factor with up to 64 GB of RAM on LGA 1151 variants. Usual DDR3 memory is also supported by certain motherboard vendors even though Intel doesn't officially support it.
- Support for 16 PCI Express 3.0 lanes from CPU, 20 PCI Express 3.0 lanes from PCH (LGA 1151), 44 PCI Express 3.0 lanes for Skylake-X
- Support for Thunderbolt 3 (Alpine Ridge)
- 64 to 128 MB L4 eDRAM cache on certain SKUs
- Up to four cores as the default mainstream configuration and up to 18 cores for X-series
- AVX-512: F, CD, VL, BW, and DQ for some future Xeon variants, but not Xeon E3
- Intel MPX (Memory Protection Extensions)
- Intel SGX (Software Guard Extensions)
- Intel Speed Shift
- Skylake's integrated Gen9 GPU supports Direct3D 12 at the feature level 12_1
- Full fixed function HEVC Main/8bit encoding/decoding acceleration. Hybrid/Partial HEVC Main10/10bit decoding acceleration. JPEG encoding acceleration for resolutions up to 16,000×16,000 pixels. Partial VP9 encoding/decoding acceleration.
- The L1 cache for all Skylake CPUs consists of two parts: data and instructions, whereas the former is equal to 32KB times the number of cores, and the latter is calculated the same way. So, e.g. for a six core model it will be equal to 32*6 + 32*6 = 384KB.
Configurations
Skylake processors are produced in five main families: Y, U, H, S, and X. Multiple configurations are available within each family:
List of Skylake processors
Mainstream and high-end desktop processors
Common features of the mainstream desktop Skylake CPUs:
- DMI 3.0 and PCIe 3.0 interfaces
- Dual channel memory support in the following configurations: DDR3L-1600 1.35 V (32GiB maximum) or DDR4-2133 1.2 V (64GiB maximum). DDR3 is unofficially supported through some motherboard vendors
- >=16 PCI-E 3.0 lanes
- The Core-branded processors support the AVX2 instruction set. The Celeron and Pentium-branded ones support only SSE4.1/4.2
- 350 MHz base graphics clock rate
Common features of the high performance Skylake-X CPUs:
- Quad channel memory support for DDR4-2400 or DDR4-2666 up to 128GiB
- 28 to 44 PCI-E 3.0 lanes
- In addition to the AVX2 instruction set, they also support the AVX-512 instructions
- No built-in iGPU (integrated graphics processor)
- Turbo Boost Max Technology 3.0 for up to 2/4 threads workloads for CPUs which have 8 cores and more (7820X, 7900X, 7920X, 7940X, 7960X, 7980XE)
- A different cache hierarchy (in comparison to mainstream Skylake CPUs)
Mobile processors
See also "Server, Mobile" below for mobile workstation processors.
Workstation processors
- All models support: MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, AVX, AVX2, AVX-512, FMA3, MPX, Enhanced Intel SpeedStep Technology (EIST), Intel 64, XD bit (an NX bit implementation), Intel VT-x, Intel VT-d, Turbo Boost (excluding W-2102 and W-2104), Hyper-threading (excluding W-2102 and W-2104), AES-NI, Intel TSX-NI, Smart Cache.
- PCI Express lanes: 48
- Supports up to 8 DIMMs of DDR4 memory, maximum 512 GB.
Server processors
E3 series server chips all consist of System Bus 9 GT/s, max. memory bandwidth of 34.1 GB/s dual channel memory. Unlike its predecessor, the Skylake Xeon CPUs require either a C232 or a C236 chipset to operate.
"Skylake-SP" (14 nm) Scalable Performance
- Xeon Platinum supports up to 8 sockets. Xeon Gold supports up to 4 sockets. Xeon Silver and Bronze support up to 2 sockets.
- -M: 1.5TB RAM per socket vs 768 GB for non-M SKUs, -F: integrated OmniPath fabric, -T: High thermal-case and extended reliability
- Support for up to 12 DIMMs of DDR4 memory per CPU socket.
- Xeon Platinum, Gold 61XX, and Gold 5122 have two AVX-512 FMA units per core. Xeon Gold 51XX (except 5122), Silver, and Bronze have a single AVX-512 FMA unit per core.
Xeon Bronze and Silver (dual processor)
- Xeon Bronze 31XX has no HT or Turbo Boost support.
- Xeon Bronze 31XX supports DDR4-2133 MHz RAM. Xeon Silver 41XX supports DDR4-2400 MHz RAM.
- Xeon Bronze 31XX and Xeon Silver 41XX support two UPI links at 9.6 GT/s.
Xeon Gold (quad processor)
- Xeon Gold 51XX has two UPIs at 10.4 GT/s. Xeon Gold 61XX has three UPIs at 10.4 GT/s.
- Xeon Gold 51XX support DDR4-2400 MHz RAM (except 5122). Xeon Gold 5122 and 61XX support DDR4-2666 MHz RAM.
Xeon Platinum (octa processor)
- Xeon Platinum has three UPIs at 10.4 GT/s.
- Xeon Platinum supports DDR4-2666 MHz RAM.
Source of the article : Wikipedia
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