| | | | Accelerated Graphics Port. A graphics card expansion slot launched in 1997 and created largely by Intel for it's Pentium processors, specifically to cope with the throughput demands of 3D graphics on PCs (although also seen in integrated onboard graphics). In order to use AGP the motherboard's chipset must also support it. Rather than using the PCI (Peripheral Component Interconnect ) bus as had been the case with previous (still manufactured) graphics cards, AGP has a direct route from the graphics controller to the main memory. It is able to store graphics data such as 3D images in system memory rather than video memory and runs at several times the speed of PCI too (66MHz). Another speed advantage comes from the way AGP handles data - unlike PCI where the entire data packet has to be read to determine addressing information, AGP uses sideband addressing which allows this information to be read outside the data packet, saving time. AGP is not strictly a bus because an AGP controller can only control one device, although multiple AGP controllers on the same motherboard can control multiple AGP cards (not common). The first AGP standard was capable of a throughput of 264MB/sec, then came AGP 2x at 528MB/sec. AGP 4x increased it further to 1 GB/sec and the fastest, AGP 8x, runs at 2GB/sec. Cards from later generations are backwards-compatible with earlier standards and have notches/keys to ensure there is no mismatch (different generations used different voltages - 1.5V and 3V - and fitting a 1.5V card to a 3V slot could damage it). AGP is in the process of being superceded by PCI Express which has much greater potential data transfer and is cabable of sending and receiving data at the same time (duplex). | | | |
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