P35 Express – PCI ExpressOn paper, the P35 doesn’t appear too much different from the P965 in terms of PCI Express management. The MCH manages 16 lines, which are only attributable to a single peripheral. This is in contrast with the 975x, which can manage 2x8 lines. The second PCI Express x16 port that we find on some motherboards actually uses the ICH’s four PCI Express lines . This of course has a non negligible impact on performances in certain cases, which we will illustrate in three separate tests :
- Serious Magic, a test which carries out a download of the graphic card from the system
- SPECViewperf9 UGS Teamcenter, a graphic OpenGL simulation, simulating a very heavy professional use
- 3DMark2006, here the score of two HDR/SM3.0 scenes in 1920*1200
The graphic card was a NVIDIA GeForce 8800 GTX , combined with an E6700 and 2 GB of DDR2-800 4-4-4-12.
The download test logically shows a strong decrease in transfer rate, which however is not divided in four. In x16, we were at 30% of the theoretical transfer rate and this figure attained 69% in x4.
SPECViewperf shows a similar performance ratio and going into x4 therefore has a large effect on performances for this type of very heavy load.
3DMark06, representing a graphic load that is closer to games of the last generation, is affected but to a lesser extent. However, the difference between a x4 and x16 port allow a performance gain from 27 to 29%!
As you can see, it is really unfortunate that Intel didn’t do better than a x4 on a second PCI Express port. The solution used for the i975x, dividing its 16 lines between two peripherals, is more advantageous, because the impact of a single x16 port on gaming performances is low.
We will have to wait for the future X38, which should allow the management of two x16 ports via its MCH, so that we can have a DDR3 chipset capable of properly managing two graphic cards, whether managed one at a time or in pairs. If it’s not SLI compatible, which remains a guarded reserve for NVIDIA and its nForce, the P35 is CrossFire compatible like the P965.