14 DAY TRIAL // The PCI-Express technology for graphics cards came to replace the previous AGPX8 format by mid 2004, but at that time, performance gains were minimal. Later on, although performance gains were irrelevant, GPU integrators had to abandon the AGP solutions, concentrating on the heavily promoted PCIe format. With the improved bandwidth provided by the PCI-e slots, NVIDIA launched SLI versions starting with their GeForce 6XXX series GPUs.
NVDIA specifically stated that the SLI configurations do not work on the previous AGP slots. According to NVIDIA, SLI technology was designed for PCI Express only, because the new bus had superior bandwidth (two to four times that of AGP 8X), support for isochronous data transport, and the capability to drive multiple high-speed graphics devices. The now obsolete AGP 8X bus remained limited to one high-speed graphics device and NVIDIA considered that this type of bus was not a candidate for SLI technology.
Despite NVIDIA's statements, users of the ocworkbench.com forums demonstrated that SLI configurations work fine on AGP slots. Moreover, one could couple one AGP card with a PCI-e one to form a completely stable SLI configuration. The guys over at ocworkbench even used different NVIDIA GPU families ? an AGP NV43 (6600GT) and a PCI-e NV73 (7600GS) - installed on an Asrock 939Dual-SATA motherboard with modified drivers. The NV43+NV73 SLI configuration wasn't actually benchmarked, but the guys managed to run thorough tests on a 7600GS AGP card coupled with a 7600 PCI-e one.
The test system was powered by an AMD 64 3000+ (1800Mhz) Winchester Core CPU with 512KB L2 cache, which was overclocked to 2250MHz. System memory was provided by four Kingston DDR400 modules and tests were conducted under Windows XP Professional SP2 installed on a Western Digital 80GB PATA HDD. The SLI configuration was enabled using the modified 85.96 driver.
The PCI-e+AGP configuration scored 2569 marks in 3Dmark05 set at 1600 x 1200, while a PCI-e card alone scored 2517 marks. Nearly no performance improvement, but the testers claim that a more powerful CPU combined with a monitor that supports high resolutions could lead to a significant performance boost.