What is a PCI Express Video Card?

A video adapter, or video "card" is a set of chips and circuits which translates data into a signal that a monitor or display can translate into a visible image. For all intents and purposes, this signal is nearly always digital, unless the card is designed to drive some kind of analog display.

Some video adapters can do quite a bit more than just the basic function of translating the instructions of the computer processor into a instructions for a display. Most video cards are now equipped with hardware functions or "instruction sets" which provide programmers access to very advanced and highly optimized fast routines for "rendering" geometry in displays of 3D data, for example.

These video cards have improved from early models with only a few kilobytes of memory up to capacities of 512MB and 1GB of RAM on each card. This makes it possible for the card to store one or more entire sets of instructions or a "virtual display" within its own RAM. These video adapters can increase the speed and smoothness of the display dramatically, because retrieving this information from the video card's memory is far easier and faster than asking the computer's CPU to retrieve the information from the system's memory, then send it to the video card. Speed is essential, becuase video cards must refresh the display many many times each second.

PCI express is a type of bus which is installed on a system's mainboard. A bus is simply an electronic circuit which takes data from one place and sends it somewhere else. There are buses on mainboards for the CPU, and for many of each system's peripheral devices, such as video adapters and sound cards.

Early systems used something called ISA, which stands for "Integrated System Architecture." Every device attached to ISA mainboards used the same bus. Unfortunately, compared to later bus architectures, ISA was very slow, and it was difficult to do much with graphics for games, for example, because game programmers had to write their own graphics routines and had to rely on the system's CPU and RAM to refresh the display.

The ISA bus was replaced by the PCI bus, and another faster architecture called AGP was later added specifically for video adapters. As these new architectures became available, bus speeds increased to the point where it became practical to use the video card as a sort of "graphics subsystem" instead of the main CPU and RAM. PCI Express recently replaced AGP and is the current standard for video adapters.