Skylake-X gets wider and cachier
While we don't have full details of how the server version of Skylake stacks up against its mainstream desktop counterpart yet, Intel has let slip a few details. First off, Intel has implemented AVX-512 support with Skylake-X. That means the width of each AVX data register has doubled compared to the desktop version of Skylake, which uses 256-bit-wide registers.
AVX-512 support also nets 32 data registers for Skylake-X, compared to 16 for typical desktop Skylake. In theory, AVX-512 will yield a doubling of the FLOPS per second per core compared to Intel's older architectures. You'll hear Intel call the Core i9-7980XE its "first teraflop CPU," and the move to AVX-512 is why. Assuming developers recompile their software to use AVX-512 instructions, SIMD-heavy programs could get a big speedup from these chips.
In perhaps the biggest change to its microarchitecture, Skylake-X also introduces a new cache hierarchy. Each core now has a 1MB private L2 cache, up from 256KB in mainstream Skylake cores. The shared last-level cache, or L3, for Skylake-X has shrunken a bit in turn, to as much as 1.375MB per core. Broadwell-E boasted as much as 2.5MB of L3 cache per core. This new L3 structure is no longer inclusive of the L2 cache, either, as it was with Broadwell-E. As a rule of thumb, quadrupling the cache size as Intel has done here will cut the miss rate in half, assuming the same associativity. We'll be digging for more details of these changes when we meet with Intel about its X-series CPUs soon, but expect a major performance boost from this rejiggering of the caches on Skylake-X regardless.
It's not strictly a microarchitectural feature, but Skylake-X also debuts a new take on Intel's Turbo Boost Max 3.0 technology, first seen with Broadwell-E chips. In the first iteration of Turbo Boost Max 3.0, Intel identified the highest-boosting core on a Broadwell-E die. In tandem with a Windows driver, TBM 3.0 could let those high-potential cores boost well above their normal Turbo speeds for high performance in lightly-threaded workloads. This time around, Intel is snooping out the best two such cores on a Skylake-X die for even more of a performance improvement, and no more Windows driver is needed to let TBM 3.0 work its magic. Intel also tells us to expect more consistent support and implementation of the TBM 3.0 feature from motherboard manufacturers this time around, a welcome improvement compared to the state of the feature on Broadwell-E motherboards.
The X299 platform takes a dip in Kaby Lake
To host Skylake-X and Kaby Lake-X CPUs, Intel is introducing a new socket, called LGA 2066, and a new chipset, called X299. We'll be covering many, many X299 motherboards this week from Computex, but here are the basics. LGA 2066 uses more pins than LGA 2011v3 before it, but its outer dimensions are identical to the older socket's. Builders will obviously need new motherboards to build with Core X-series chips, but they'll at least be able to reuse their existing cooling hardware.
The X299 chipset might also evoke some deja vu among observant gerbils. That's because Intel based the X299 PCH on its consumer Kaby Lake chipsets, rather than following in the footsteps of the server-sourced X99 PCH. The infusion of Z270 in the X299 chipset offers several benefits to Intel's high-end desktop platform, although it breaks little new ground. That said, X299 upgrades the link between the CPU and the chipset to DMI 3.0, which offers roughly the same bandwidth as four lanes of PCIe 3.0. Broadwell-E still relied on the X99 platform's DMI 2.0 link.
X299 also gives motherboard makers 30 flex I/O lanes to play with. Those flex lanes can be configured as up to 24 PCIe 3.0 lanes, as many as eight SATA 6Gbps ports, and up to 10 USB 3.0 ports. Thanks to its Z270 roots, however, X299 still doesn't boast onboard USB 3.1 Gen2 support, so expect that connectivity to come by way of external controllers on X299 mobos.
X299 will also support Intel's Optane Memory and Optane SSD technologies. We doubt many X299 builders will still be considering using hard drives as boot devices, but Intel plans to offer a full-bore 3D Xpoint SSD later this year that seems like a perfect complement for a Skylake-X system. When that storage device arrives, X299 PCs will be ready for it.
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