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I have a motherboard with a PCIexpress x16 slot.

I want to purchase a card called AMD Radeon HD 7770, which uses PCIe version 3.0.

Is that back compatible?

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@Ernie is correct. Any PCIe v3 card will work in a PCIe v2 slot. AQlso, you do not list which version of PCIe your x16 slot is. We all assume you mean v2, but it could be v1, v2 or v3, since the versioning is independent of the number of lanes (which is the x1, x4, x8, x16 part). –  Hennes Jan 29 '13 at 0:40

2 Answers 2

Quoting wikipedia:

PCI Express 3.0 Base specification revision 3.0 was made available in November 2010, after multiple delays. In August 2007, PCI-SIG announced that PCI Express 3.0 would carry a bit rate of 8 gigatransfers per second (GT/s), and that it would be backward compatible with existing PCIe implementations.

Emphasis is added.

So yes, the card will work in the slot, but as nerdwaller mentioned, you may not get full performance depending on the resolution or framerates you're aiming for.

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Aye, performance is likely to be around 1% slower in a PCIe v2 x16 slot compared to a PCIe v3 x16 slot. This is because we do not use the full bandwidth of PCIe v3 x16 yet. –  Hennes Jan 29 '13 at 0:44

You should try researching this a bit before asking, but it should work fine.

The issue would be if you are trying to hit really high resolutions. Just verify that the BIOS on your MOBO is up to date (check the version history to see if it's needed before needlessly flashing it).

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