Single graphics 16x or crossfire 8x


Oct 24, 2009

I have a Gigabyte P55 UD6 and currently have a Gigabyte HD5870. I am considering putting in another GPU and running 2 HD5870's in Crossfire, however I note that the speed of one card is 16 x and the speed of 2 cards drops to 8 x. Is there any real benefit in getting the additional card? Are 2 cards running at 8 x better than 1 running at 16x?



Jun 1, 2009
Of course 2 cards will be faster. 16x and 8x is not the speed of the cards, it is a measurement of the speed of data transfer between your graphics card and your system via PCI express.

The lynnfield/p55 platform (like yours) has the PCI express controller in the cpu, your cpu can give 16 lanes of PCI express, so when you use 2 cards each will get 8 lanes. Higher end bloomfield/X58 systems can have 2 cards with each receiving the full 16x bandwidth.

The speed of PCI express (number of lanes: 8 or 16) can have some effect on performance but it is usually minor, more powerful cards can benefit from higher bandwidth, but even in the case of HD 5870, the performance will not differ by more than 10% between 2 cards in x8 and 2 cards in x16. (there are reviews around the web).

However, a single HD 5870 is a very fast card and should be enough even for gaming at 2560*1600, unless you game at very extreme settings. For sure you will get higher frame rates from 2 cards in crossfire, but I don't think the cost is justifiable.

Have a good luck