PCI-Express x16 Basics
PCI-Express x16 is the type of PCI-Express slot used by the Intel 915 and 925 and other chipsets which support PCI-Express. PCI-Express x16 offers 16 PCI-Express lanes, providing peak bandwidth of 4GBps in each direction, compared to AGP 8x's 2.1GBps total bandwidth (each PCI-Express lane provides 250MBps of bandwidth in each direction).
Although PCI-Express x16 is capable of 4GBps bandwidth in each direction, whether a particular video card provides this performance level is determined by its internal design. To achieve the full level of performance available with PCI-Express x16, ATI believes that a video card should use a native implementation, which connects the PCI-Express bus interface on the video card directly with the PCI-Express bus. This is the approach ATI uses with its X-series line of GPUs and graphics cards. The other method is the bridged approach, which uses an AGP-to-PCI-Express bridge chip to connect an AGP-based GPU to the PCI-Express bus. NVIDIA uses the bridged approach with its GeForce 6800 GPU series.