Graphics Interconnect Comparison - PCI Express vs AGP 'Express'
ECS's bonded PCI Conventional approach for the AGP 'Express' slow yeilds a 266MB/sec connection to the MCH (from what I can tell, the tools I have to mention the port's clock rate aren't happy doing so) but without the ability to do things like DIME, that AGP provides. So the bandwidth is around that of an AGP1X slot, but you can't bypass the CPU when accessing data bound for the graphics card that's sitting in main memory.We use our usual graphical tests to measure the impact of using the AGP Express slot, by using a pair of 6800 GTs, one of each type.
Painkiller
34% of performance is lost by using the AGP Express port on the 915P-A, in Painkiller. The limitations on the port, as far as its full compatibility with AGP go, are clear. It allows you to use an AGP graphics card, but performance isn't as good. Let's confirm that with another couple of tests.
3DMark03
24% of performance is lost using the slot, with 3DMark03.
3DMark 2001SE
Only 17% is lost with 3DMark 2001SE, a majority DX8.1 benchmark. ECS's own benchmarks on DX8.1 titles back when the board was announced showed similar losses (although much less of a performance hit using DX9 games, for some reason).
Is the AGP Express slot worth using?
Yes, it is worth using if you're an upgrader (and you should be if you're considering buying a 915P-A). Be under no illusions that the slot will cost you some absolute performance, but with a sufficiently powerful graphics card to start with, it should be usable until you can afford something PCI Express based.There are secondary benefits to using the slot too. You can use it at the same time as the PEG16X slot, to install a pair of graphics cards. Testing with a pair of X800 XT boards on PCI Express and AGP didn't let me use four monitors, but with NVIDIA boards it appeared to be usable, although I only have two monitors so I can't be 100% sure. ECS claim some success with the feature, but they don't guarantee anything.
Compatibility wise, some older AGP boards aren't compatible with the slot. Certain ATI Radeon 9500 boards are off-limits for example. In that respect, the usability of the slot is somewhat reduced, if it's not clear what graphics cards you can actually use with it.
Overall I had good success with a trio of AGP boards that I tried with it (X800 XT PE, 6800 GT, 9800 XT), so it's worth using if you can stomach the performance hit.
Click for a bigger version
