I have seen a lot of questions regarding whether or not one's P67/Z68 motherboard supports PCI Express 3.0. To clear up the confusion I decided to take what I have written in the past and post it here with some editing.
First PCI Express has the maximum of 16 lanes, whether this is PCI Express 2.0 or PCI Express 3.0. PCI Express 3.0 has doubled the performance of 2.0. On 2.0 each lane can do 1 GB/s; on 3.0 each lane can do 2 GB/s. Think of this as a freeway. No widening is done, but the speed limit has doubled. PCI Express that graphics card(s) use comes from the CPU itself.
(See how PCI Express 2.0 x16 is wired directly to the CPU, CPU is 2nd Gen Sandy Bridge).
(Again, see how PCI Express is coming from the CPU directly).
Sandy Bridge CPU has PCI Express 2.0 controller built inside.
Ivy Bridge CPU has PCI Express 3.0 controller built inside.
So how come there is Gen3 motherboard going on? Why can't you just swap the CPU and have PCI Express 3.0? Answer to that is PCI Express switches. PCI Express switch is used to split a single 16 lanes into two 8 lanes. On motherboard that supports SLI setup, Nvidia mandates that both GPUs are to connect to the CPU directly. Since CPU itself can only supply a single 16 lanes, a gizmo called PCI Express switch is used to split it into two 8 lanes. This is from Gigabyte GA-Z68XP-UD3 (a motherboard that supports SLI) manual, page 8.
See how PCI Express switch sits between the slot and the CPU? This thing determines whether or not you are going to have PCI Express 3.0. Intel did not have any plan with PCI Express 3.0 when Sandy Bridge platform was first released. As a result motherboard manufacturers use PCI Express 2.0 switches on Gen2 motherboards. Which is why you cannot use PCI Express 3.0 on Gen2, because the switch, whom supposed to split x16 into two x8, doesn't support 3.0. Now take a look at GA-Z68A-D3-B3, a motherboard that does NOT support SLI.
Since it only has one x16 slot, all 16 lanes are connected to the CPU directly. No switch is used. Therefore when you install Ivy Bridge it will run at PCI Express 3.0.
In fact, on ASRock website,
Quote:
On ASUS website:
Notice how motherboards from above either are Gen3, or that they don't support SLI (single x16 slot).
http://event.asus.com/2011/mb/pcie3_ready/
Summary:
* When Sandy Bridge is used with any LGA1155 motherboard, it will always run at PCI Express 2.0. Always.
* When Ivy Bridge is used with motherboard that does not support SLI, it will run at PCI Express 3.0.
* When Ivy Bridge is used with P67/Z68 motherboard that does support SLI, it must says that it supports PCI Express 3.0 and/or Gen3 for it to support PCI Express 3.0. Otherwise it will run at 2.0.
Keep in mind that some BIOS/UEFI allow you to set the speed of PCI Express. You still have to fulfill one of the condition above to use PCIe 3.0.
PCI Express lanes coming from the chipset (x1 and x4) are still running at 2.0. It is the same with H77/Z75/Z77 chipset regardless of what CPU is used.
Z77 motherboard only: If your motherboard has a PCI Express x4 slot wired to the CPU, it can only be used when Ivy Bridge is installed. The slot will be disabled when Sandy Bridge is used. Consult your motherboard manual/diagram to find out if it is wired to the CPU or the chipset.
First PCI Express has the maximum of 16 lanes, whether this is PCI Express 2.0 or PCI Express 3.0. PCI Express 3.0 has doubled the performance of 2.0. On 2.0 each lane can do 1 GB/s; on 3.0 each lane can do 2 GB/s. Think of this as a freeway. No widening is done, but the speed limit has doubled. PCI Express that graphics card(s) use comes from the CPU itself.
(See how PCI Express 2.0 x16 is wired directly to the CPU, CPU is 2nd Gen Sandy Bridge).
(Again, see how PCI Express is coming from the CPU directly).
Sandy Bridge CPU has PCI Express 2.0 controller built inside.
Ivy Bridge CPU has PCI Express 3.0 controller built inside.
So how come there is Gen3 motherboard going on? Why can't you just swap the CPU and have PCI Express 3.0? Answer to that is PCI Express switches. PCI Express switch is used to split a single 16 lanes into two 8 lanes. On motherboard that supports SLI setup, Nvidia mandates that both GPUs are to connect to the CPU directly. Since CPU itself can only supply a single 16 lanes, a gizmo called PCI Express switch is used to split it into two 8 lanes. This is from Gigabyte GA-Z68XP-UD3 (a motherboard that supports SLI) manual, page 8.
See how PCI Express switch sits between the slot and the CPU? This thing determines whether or not you are going to have PCI Express 3.0. Intel did not have any plan with PCI Express 3.0 when Sandy Bridge platform was first released. As a result motherboard manufacturers use PCI Express 2.0 switches on Gen2 motherboards. Which is why you cannot use PCI Express 3.0 on Gen2, because the switch, whom supposed to split x16 into two x8, doesn't support 3.0. Now take a look at GA-Z68A-D3-B3, a motherboard that does NOT support SLI.
Since it only has one x16 slot, all 16 lanes are connected to the CPU directly. No switch is used. Therefore when you install Ivy Bridge it will run at PCI Express 3.0.
In fact, on ASRock website,
Quote:
http://www.asrock.com/microsite/pcie3/overview.html
On ASUS website:
Notice how motherboards from above either are Gen3, or that they don't support SLI (single x16 slot).
http://event.asus.com/2011/mb/pcie3_ready/
Summary:
* When Sandy Bridge is used with any LGA1155 motherboard, it will always run at PCI Express 2.0. Always.
* When Ivy Bridge is used with motherboard that does not support SLI, it will run at PCI Express 3.0.
* When Ivy Bridge is used with P67/Z68 motherboard that does support SLI, it must says that it supports PCI Express 3.0 and/or Gen3 for it to support PCI Express 3.0. Otherwise it will run at 2.0.
Keep in mind that some BIOS/UEFI allow you to set the speed of PCI Express. You still have to fulfill one of the condition above to use PCIe 3.0.
PCI Express lanes coming from the chipset (x1 and x4) are still running at 2.0. It is the same with H77/Z75/Z77 chipset regardless of what CPU is used.
Z77 motherboard only: If your motherboard has a PCI Express x4 slot wired to the CPU, it can only be used when Ivy Bridge is installed. The slot will be disabled when Sandy Bridge is used. Consult your motherboard manual/diagram to find out if it is wired to the CPU or the chipset.