Skylake x in mac pro, only goes up to 10 cores. Marketing wise thi wouldnt be great for apple, so it makes sense for apple to go for the EP variant.
It wouldn't be Skylake-X it would be Skylake-W but the core count there probably won't be much of a difference.
What has been historically EP variant is being split into two different sockets (and essentially products). This has been on the Intel roadmap for
years at this point. Circa 2015 or so:
http://www.cpu-world.com/news_2015/2015052701_Details_of_Intel_Purley_server_platform_leaked.html
Note that in 2016-2017 the 1 and 2 processor are being implemented on the same platform: Grantly-EP 1S and 2S ( one / two socket). As of late 2017 ( which will be Q3-Q4 17) that splits into
two separate platforms. Purley ( primarily aimed at 2+ sockets ) and Basin Falls aimed squarely at 1 socket workstation solutions. Two separate sockets. Two separate PCH chipsets.
Purley has a bunch of stuff that don't make much sense on the vast majority of workstations. OmniPath.
Four 10GbE socket support in the PCH. Intel is going to charge serious dollars for that stuff. If you are not using most of it in your system, then you'll be wasting substantial money because Intel
is going to make you pay for it.
Socket R (
https://en.wikipedia.org/wiki/LGA_2066) is really far, far closer to what Apple has been using all along. Before the split there were typically 2-3 dies that comprised the EP products. One "low core count" (lcc) and of late a "medium count" (mcc) and "high count". All three have pictures here (
http://www.anandtech.com/show/10158/the-intel-xeon-e5-v4-review/2 ) but this is the medium and the low.
The there is a 'layer cake' of a stack of 5 bound together with some token ring like networking loops. The lcc has been the typical Xeon E5 1620-1680 range ( with direct mappings of these dies back to the -E Core i7 HEDT implementations using the exact same die with different functionality turned off/on. )
If skylake x went over 10 cores then it could make sense.
There is a very good chance there are not going to be any reasonably priced 4-6 core variants in the E5 2600 v5 range. ( that x6xx may change because new socket, perhaps 2700 but in that case there won't be a 2600. ). the Medium and High core counts will be the only options they build. The lcc would be separate and have substantively different uncore ( memory , pci-e , etc ) implementation since targeting a very different socket. ( no OmniPath , no very high number of DIMM memory banks, etc. etc. )
Nothing at the smaller end makes even less sense marketing wise for Apple than some tech porn lust high core count at the top. 10 cores at a 10% higher clock rate is better than 12 cores at a clock rate that is 20% lower that higher one for vast majority of Mac Pro user base.
One reason why Intel will probably stick with a 5 layer cake for the lcc versions instead of moving to a 6 layer ( max out at 12 cores) is that they'll want to get to 10nm faster with a smaller die.
Intel is on track to split the mcc and hcc designs into smaller chunks and use an external ASiC/FGPA/custom die to glue those back together again. Embedded Multi-Die Interconnect Bridge (EMIB). detailed at the end of this article. (
http://www.anandtech.com/show/11115...n-core-on-14nm-data-center-first-to-new-nodes ). Intel really don't need 6 layer designs going forward. Stacks of 5 (up to 10) bolted together to from 20 , 30 , 40 is enough for the higher core counts. That is what they were primarily doing internally anyway until started to hit the borders or large die sizes at smaller geometries.
Second, even at 14nm++ process that v5 (Skylake) will use, the 5 layer die is going to be cheaper to produce than a 6 layer one. AMD's Zen implementation is a creditable threat. This is heat from cost pressure for their workstation product offering. A bigger die isn't going to help with that. 14nm++ is going to get some moderately high 3D packing of the transistor but there is not overall huge shrink to pack 2 more cores and their associated 1.5MB worth of cache into the same amount of space.
Intel does the 6 layer stacks on the hcc die because they are charge "nosebleed" high prices for those product $2000+. It is a humongous die with likely lower yields.
So HP and Dell will probably have 2P Large Workstations that they sell with only one socket filled. Some of those will be in the 15 core range, but that is highly likely larger than Apple is aiming at. However, there Basin Falls 1P workstation Xeon E5 1xxx v5 products are going to have the same count count cap as the Apple product will. There is no marketing "falling sky" issue there at all.
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From the way Apple is talking, I would be really surprised if Apple stepped back to the enthusiast parts. The E5 series sounds like where they will stay (unless they do something like Ryzen which would surprise me.)
Xeon E5 16xx and Core i7 HEDT are essentially the same die with some parts turns off/on depending upon the market segment. The core counts are a fundamental property of the die. They aren't going to radically change.
In the past the E5 1600 and 2600 parts shared the same socket. That was history that isn't the future. Intel has been laying roadmap for that split for years at this point. I highly doubt Apple is going to be blindsided by it as their NDA briefing are much better than the stuff that leaks out onto the Internet (from which materials the split is clearly outlined.).
All modern Macs already have. They just don't have PCIe slots.
"... If you have an Intel-based Apple system, it has a UEFI firmware, though there are special considerations involved in installing and booting Fedora on Apple systems due to the special Apple boot interface built on top of UEFI. ... "
https://fedoraproject.org/wiki/Unified_Extensible_Firmware_Interface
There is Apple stuff on top of the base layer. That's what I meant by implementing in its entirety. But yes the differences between the early boot stages and transitioning into handing things off to a bootstrapping macOS you do start to leave EFI directly and get into a OS specific loaders. That's where missing boot screens show up.
Apple isn't really proactively blocking folks with their UEFI/EFI ( .e.g, they could have turned on Secure boot to throw up active roadblocks ), but I doubt they are going to bend over backwards to make the OS bootstrapping process more Windows like to make the cards easier to use.