Kaby Lake-X and Skylake-X processors

Core i9 and Core X series processors

Intel has Skylake-X processors to offer. Where the previous and current Broadwell-E platform had up-to 10-core processors (Core i7 6950X), Intel expanded on that with many-core proc offerings. Intel markets the new series as the Core X series, and is also adding a denominator, the Core i9 series. The new processors are paired with a new chipset, X299 and socket LGA2066.
 

Architecture changes

The new Core i9 series processors are based upon the Skylake architecture that you know from the socket 1151 parts, but scaled upwards. The processor series is fabbed at 14nm. Despite being based upon the Skylake architecture, there are some changes to address. IPC has been improved meaning the number of instructions per clock-cycle has been improved. Skylake-X offers an up-to 8% performance increase in IPC. It’s always hard to tell how correct that number is, as Intel in the past simply increased clock frequencies and called that an IPC increase. That, opposed to expensive architecture changes in caches and so on. However, Intel did change its caches, the L2 cache, for example, has been increased from 256 kB to 1 MB per core, which really is significant. However, relative to that the L3 cache was 2.5 MB and these days is 1.375 MB per core, which thus is smaller compared to Broadwell-E. Intel thus tweaked and balanced out the L2 and L3 caches. With the new processors, you will also see two Turbo modes dubbed 2.0 and 3.0. We’ll keep it simple, but basically, with Turbo mode 3.0 fewer threads will clock higher. E.g. for a low threaded application a processor could boost with 2 cores to, say, 4.5 GHz. Whereas when Turbo mode 2.0 kicks in, it would do, say, 4 threads at 4.2 GHz. Intel also stepped away from the aging ringbus architecture and now is using a mesh design for inter-component communication. 

The processor Socket

The refresh Skylake-X processor series brought Socket 2066 to the new X299 chipset platform, with Skylake-X and Kaby Lake-X at the time. The difference is simple, Skylake-X can offer 18, 16, 14, 12, 10, 8 and 6 core processors (+ threads). The other (Kaby Lake-X) remains to be a quad-core part. So Kaby Lake-X processors will physically fit onto the X299, it, however, ends up being just a dual-channel memory part. Intel has phased out Kaby Lake-X.
  

 
A new socket, LGA2066, and yes -- that means that once again you have to purchase a new motherboard. This chipset will be called X299, it will offer dual-channel memory for Kaby Lake-X processors, and for the Skylake-X processors, you get quad-channel support (up-to 2667 MHz). And yes, that means from the four to eighteen-core procs, they will all fit the (expensive) X299 motherboards. There are some changes that you will need to be aware of. First off, the DMI interface (the IO interconnect in-between the processor and chipset) is getting more bandwidth, roughly 4 GB/s. That means you’ll have more PCIe lanes available for other connections in the IO like SATA, M.2, USB and so on. This is needed as Intel still did not embed USB 3.1 Gen 2 or Thunderbolt 3 inside their processors and thus the motherboard partners rely on external 3^rd party chips (and this connection) for such implementations. The X299 chipset, however, does offer Gen 1 USB 3.1 ports.

The processor and PCI-Express

• Kaby Lake-X quad-core procs get 16 PCI-Express Lanes 3.0
• Skylake-X six and 8-core procs get 28 PCI-Express Lanes 3.0
• Skylake-X ten to 18-core procs get 44 PCI-Express Lanes 3.0

The Kaby Lake-X procs will support dual-channel DDR4 and only 16 PCIe 3.0 lanes, this will be 44 PCIe 3.0 lanes for the most high-end Skylake-X models, not including the 6 and 8-core parts which will get 28 PCIe lanes. That means in the year 2017 with a 599 USD Core i7 7820K processor you still cannot get full x16 each with two graphics cards. The new platform also offers support for Intel Optane. 

The chipset and PCI-Express

In-between the processor and the chipset there is an updated, faster DMI 3.0 link (equivalent to a full PCIe 3.0 x4 link). Now, you will have noticed that many motherboards will offer two or three M.2 storage units. So how would that work out with a X16 gen 3.0 processor you wonder? Well, the X299 chipset adds up to another 20 to 24 Gen 3.0 PCIe lanes. It is here the extra 3rd party SATA / USB controllers and thus M.2 storage units can draw their bandwidth from.