Please tell me: What is difference between PCIe 2.1 x16 and PCIe x16

Dorado said:

I agree with bobkn: PCI-E 2, 2.1 and 3 graphics cards are supposed to be backwards compatible with older PCI-E 1 or 1.1 slots.

But i experienced issues with Radeon HD 5xxx series GPUs on my 2nd pc's motherboard (which supports only PCI-E 1.1). They are all PCI-E 2.1 cards and my motherboard seems to be incompatible with them. I solved installing a PCI-E 2.0 GPU, the GeForce GTS 450.

So, before installing new graphics cards on non-new hardware, check in internet if some people have issues with it...

Wouldn't happen to be an ASUS board would it?
I had the same problem with my old one, asus tried to blame the graphics card, which to this day works just fine in my backup machine.

I will never use ASUS again because of the way they tried to railroad me.
It was a top dollar republic of gamers board too.

Also when looking at mobo (motherboard) specifications, you have (as example) x16 slots and x16(x8 mode) slots:

An example is a ×8 slot that actually only runs at ×1. These slots allow any ×1, ×2, ×4 or ×8 card, though only running at ×1 speed. This type of socket is called a ×8 (×1 mode) slot, meaning it physically accepts up to ×8 cards but only runs at ×1 speed. This is also sometimes specified as "×size (@×capacity)" (for example, "×16(@×8)"). The advantage is that it can accommodate a larger range of PCIe cards without requiring motherboard hardware to support the full transfer rate. This keeps design and implementation costs down.

So even if it looks like a x16 slot, it might be wired as a lower speed slot. your mobo documentation will state which x16 slots are true and which are wired lower.


Here is a good example in video at 5:40 minute mark:
this board has two x16 slots and two x16 physical slots that run at x4 speed ~ x16 (x4 mode) or x16(@x4)



Also from the wiki, the difference (and similarities) between 2.0 and 2.1:

PCI Express 2.1
PCI Express 2.1 supports a large proportion of the management, support, and troubleshooting systems planned for full implementation in PCI Express 3.0. However, the speed is the same as PCI Express 2.0. Unfortunately, the increase in power from the slot breaks backward compatibility between PCI Express 2.1 cards and some older motherboards with 1.0/1.0a, but most motherboards with PCI Express 1.1 connectors are provided with a BIOS update by their manufacturers through utilities to support backward compatibility of cards with PCIe 2.1.