5850 bottleneck with PCIe x4?

[tankskun]

Would a HD5850 be a badly bottlenecked with PCIeX4 lane?

I bought a J&W Mini ITX 780G-SP128MB board & only just found out it supports up to x4 for the graphics card slot

advice please

 

[phatboy]

i would imagine it is going to have an effect mate yep,

ATI cards scale better than Nvidia which is a bonus, but you could lose up to 20% performance i think....correct me if I am wrong anyone

 

[tankskun]

o carp. i thought as much

anyone know what card is max for x4 lane bandwith? cheers

 

[Muel]

Fair bottle neck aye.

Putting current graphics cards in a PCI Express x4 slot verges on madness, incurring a performance hit of between 25 and 33 percent. Even if the motherboard in question were especially cheap, the card's price/performance ratio is affected immensely. When using an x8 connection, performance also decreases, albeit only by 7 to 8 percent.

 

[Orcvader]

That review is for PCI-E 1.0a, the board uses 2.0. http://www.tomshardware.com/reviews/pci-express-2.0,1915-9.html is the review you want to look at. You can see it's only around 10% performance drop from these charts.

 

[HW91]

it's actually an 8x electrical connection according to bit tech so you should be fine

 

[Orcvader]

it's actually an 8x electrical connection according to bit tech so you should be fine

Quoted from: http://www.bit-tech.net/hardware/motherboards/2008/09/17/j-w-minix-780g-mini-itx-htpc-motherboard/2

The PCI-Express 2.0 x16 slot is only actually electrically x4 even though it has pins for x8. J&W told us that this was because of the limitation in trace count - x8 or x16 was just not feasible because it would require 8+ layers making it much more expensive. A PCI-Express x4 slot is a large compromise for gaming - it equates to the same bandwidth and means the graphics card won't be running anywhere at its full capacity. Having said that, given its size and the fact that the CPU socket is limited to 65W AM2/AM2+ CPUs, the designers haven't designed the board as a home for the Radeon HD 4870 X2 (even though technically it can fit and work).

 

[Temi_D]

Actual test result: http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/25.html

Maximum difference it will make is 5%

 

[tankskun]

few! thats a relief. around 5% drop is fine for me. cant wait to put my little itx pc together now.
thanks for the replys all