-4

I'm about to build a desktop computer and I'm trying to understand how are this PCIe lanes distributed. The goal is being able to calculate how many lanes do I need for a certain setup. I'm looking at the Asus Z170-P motherboard, which according the specifications [1]:

  • It contains the Z170 chipset.
  • You can read on the board that it is "CrossfireX Ready" which I believe implies you could plug in 2 graphic cards.
  • The specs say it has two PCIe x16 slots, one that works at x16 mode and another one that only works at x4 mode.

First, according to the Z170 chipset specifications, it supports up to 20 PCIe lanes. However, there is no single processor that fits into the LGA1151 socket with support for 20 or more PCIe lanes [2]. Why have a chipset with support for 20 lanes when the processor will only be able to handle up to 16?

Second, supported PCIe port configurations by the chipset are "1x16, 2x8, 1x8+2x4". If I were to plug in two graphic cards, would they both work at x4 mode or x8/x4 modes? Shouldn't a motherboard designed for using two graphic cards be able to handle 32+ PCIe lanes so both graphic cards work at x16 mode?

mkrieger1
  • 19,194
  • 5
  • 54
  • 65
Rock Storm
  • 1
  • 2

1 Answers1

1

The (up to) 20 PCIe lanes from the Z170 are in addition to the 16 lanes that come directly out of the CPU.

I don't see any reason that it wouldn't run one graphics card at 16x and one at 4x. But it does seem odd to me that they call it "Crossfire-ready" without 2 x16 slots.

More info on the Z170 here: http://www.tomshardware.com/reviews/skylake-intel-core-i7-6700k-core-i5-6600k,4252-2.html

prl
  • 11,716
  • 2
  • 13
  • 31