AGP, PCI and PCIe Technology Guide

AGP, PCI, and PCIe Guide

Matrox guide to different types of expansion slots and

add-in cards





A variety of graphics cards designed to be inserted into certain types of computer expansion slots. The most common slot types used by graphics cards are AGP, PCI, and PCIe and for each of these types, there are also several sub-types. The different slot types available are an important consideration when buying a graphics card or computer. This guide describes differences between these slot types and their sub-types.

AGP





The AGP (Accelerated Graphics Port) standard was introduced by Intel in 1997 and was specifically designed to connect graphics hardware to the rest of the computer. This is in contrast to connection standards like PCI which aren't limited to graphics hardware. The advantage of the AGP approach is that graphics hardware has a dedicated connection with the rest of the computer and thus graphics hardware using an AGP connection doesn't have to compete with other devices for communication resources.







The dedicated nature of AGP can be a disadvantage in that computers supporting AGP usually have only one AGP slot. This is sufficient for most needs, but can be limiting when multiple graphics cards need to be used to support multiple displays. Fortunately, computers using the AGP standard usually have other general-purpose, PCI slots that can accommodate extra graphics cards. There are also AGP graphics cards like the Matrox QID that support up to 4 monitors at a time.



Matrox QID (AGP)

graphics card





AGP also features a more direct way to access system memory. This can be useful for 3D applications that require large amounts of memory and when there isn't enough dedicated graphics memory. Graphics cards intended for 3D applications (for example, Matrox Parhelia 256MB) have large amounts of graphics memory to minimize the use of slower system memory. More direct access to system memory is useful to low-end graphics hardware built into the motherboard of a computer. Such graphics hardware typically doesn't have its own dedicated graphics memory. This type of graphics hardware is typically disabled automatically when a graphics card is installed.



The original AGP standard was extended to achieve higher maximum bandwidths. To take advantage of the extended capabilities, graphics hardware and software has to be specifically designed for the new specifications. For example, different versions of the standard use different voltages and slightly different edge connectors.



Each variation of the standard is differentiated by a multiplier indicating the differences in potential bandwidth. The base potential bandwidth of AGP is 266 MB/s (megabytes per second) and the variation of AGP associated with this bandwidth is referred to as AGP 1x (pronounced "one-ex"). With different variations of AGP, increases in potential bandwidth are achieved by multiplying the number of bits of data transferred with each clock cycle on each data line. (continue reading &aquo;)