Hi.
I've been looking at product pages for ASUS and MSI Z87 boards mainly at the M.2 functionality...
I've noticed rhe ASUS Hero and Ranger boards say...
1: The PCIe 2.0 x16 slot (PCIEX4_3) shares bandwith with PCIe 2.0 x1 and M.2 slot. The default setting is Auto Mode, which automatically optimizes the system bandwidth. If you install a PCIe 2.0 x4 device, the system will automatically detect and disable PCIe 2.0 x1 and M.2 slot.
2: The PCIe 2.0 x1 slots (PCIEX1_1/2/3) will be disabled when PCIe 2.0 x16 slot (PCIEX4_3 ) operates under x4 speed or M.2 mode.
Right...as far as i know the Z97 chipset still supports 8 PCI-E 2.0 lanes...so why would it need to disable the M.2 slot AND x1 slots if a x4 card is used? It makes sense that the M.2 slot will be disabled if a x4 card is used as they share bandwidth and M.2 uses 2 lanes in intels Z97 implementation...but surely there should be another 4 lanes for use in PCI-E x1 slots? Again...same if you use M.2 plus a x1 card in the x16 slot, it will disable the x1 slots...what's happening to those other 4 PCI-E lanes...
With MSI it's not that straight forward...and it depends on the motherboard. But basically 0 MSI boards have any restrictions regarding M.2 other than it only supports UEFI mode, not legacy and doesnt support RAID...and I can see how MSI have done this...
On the Mpower board...
3 x PCIe 3.0 x16 slots(PCI_E2, PCI_E5, PCI_E7 support x16, x8/x8, x8/x4/x4 modes)
1 x PCIe 2.0 x16 slot (PCI_E4, supports x4 speed)
3 x PCIe 2.0 x1 slots * The PCIe x1 slots (PCI_E1, PCI_E3, PCI_E6) will be unavailable when installing an expansion card in the PCI_E4 slot.
So it looks like there it has 2 dedicated lanes to the M.2 slot thereby only allowing another 4 to the PCI-E slots, which is fair enough
Other boards, for example the Xpower, Mpower max, Gaming 9, 7, 5, GD-65 have a PCI-E layout like...
3 x PCIe 3.0 x16 slots, (support x16, x8/x8, x8/x4/x4 modes)
4 x PCIe 2.0 x1 slots
So rather than having a 3rd x16 slot on the PCI-E 2.0 lanes on the chipset, it runs the 3rd on the CPU allowing full use of the x1 slots (but obviously limiting bandwidth if you run SLI and another card in the 3rd x16 slot) and not at all interfering with the M.2 slot...Also of note apparently is 2 sata ports on MSI boards will be disabled when M.2 is in use but it doesnt state if that is dependant on running in SATA or PCI-E mode...
In my own opinion which I'm sure a lot of people will argue with, MSI's implementation looks to be a lot better with regards to keeping expansion slots running. ASUS's seems pretty ham fisted if my interpretation of their specs is right (it may well not be!) but it does look like you can't run M.2 and a x4 card from the PCI-E 2.0 slot together or use PCI-E 2.0 x1 slots when using a x4 card or M.2...which is pretty poor...i really don't see how they've managed to get so little out of 8 lanes.
Other Asus boards are slightly different...the ones with sata express for example or the Z97-A which says "The PCIe x1_1/2 slots share bandwidth with M.2 Socket 3. The M.2 Socket 3 is default disabled." which is again weird since it uses PCI-E x16 slot in x2 mode and 2 x1 slots...so yeah, ASUS seemingly have misplaced 4 PCI-E 2.0 lanes...
But in the long run can Intel be blamed for wedging in functionality to the chipset while at the same time not improving other parts the fully support said new features, not at the expense of other functionality on the MB? Really seems like no thought has been put into the implementation by both Intel and ASUS while, on the face of it...just looking at product specs...MSI has tried to make the most of whats available...
Feel free to correct me on anything i may have (most likely) got wrong here :)
Bootnote...i can't imagine X99/haswell-e will have anything like this with its 40 PCI-E 3 lanes + more from the chipset...and i know there's very little available at the moment in regards to M.2 PCI-E SSDs but I'm looking ahead to the future ;) I know there's boards out there with SATA express that don't look to be so awkward but...I much prefer looking at M.2 for an OS drive rather than SATA express...