PC Hardware —

Accelerated Graphics Port (AGP)

In the early days of PCI, the major market for that technology was the high-performance display adapter. The popularity of PCI led to its dominance of the expansion-bus market for card manufacturers. Today, the PCI market includes network cards, sound cards, SCSI adapters, UDMA controllers, and DVD interfaces. That posed a problem for display-card designers: having more cards on a single bus slowed down the performance, just when the increasing popularity of 24-bit graphics and 3D rendering called for greater demands on the display system. The search was on for yet another interface; this time, the solution was a single slot-tuned for the display adapter. Once again, Intel led the way and developed the Accelerated Graphics Port (AGP).

The AGP removes all the display data traffic from the PCI bus and gives that traffic its own 525-MB per second pipe into the system's chip set and, from there, straight to the CPU. It also provides a direct path to the system memory for handling graphics. This procedure is referred to as Direct Memory Execute (DIME). The AGP data path is shown in Figure 10.6.

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Figure 10.6 AGP Direct Memory Execute offers priority access to display data

The AGP slot, if present, is the only one of its kind on the motherboard and is usually the slot closest to the keyboard connector (see Figure 10.7). It is set forward of the back PC's case than the PCI slots. APG connectors are found only on Pentium II-based and later computers or on similar CPUs from non-Intel vendors.

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Figure 10.7 An AGP slot on the motherboard