CertiGuide to A+ (A+ 4 Real)  9  Chapter 9: Graphic Cards       9  Card Components, Modes and Architecture

Buses: PCI and AGP 1 Upgrading, Troubleshooting, and Common Problems

The memory a graphics card uses is second in importance only to the GPU. Over the years, many different types of memory have been used in card architecture, including SDRAM, WRAM, SGRAM and MDRAM. These are all specialized memory architectures, specifically designed to be very good at shifting and storing graphics data. However the most common type of memory used on modern graphics cards is Double Data Rate SDRAM, or DDR for short.

DDR is almost the same as regular SDRAM, with one important difference. Whereas SDRAM can only alter data once per clock cycle, DDR can use both the rising and falling edges of a clock cycle. Coincidentally, this exact technique the AGP bus uses to achieve phenomenal data transfer rates. DDR memory is therefore synchronized to the system clock speed, which is why its speed is rated in MHZ (megahertz) instead of ns (nanoseconds).

DDR only has one real competitor in terms of speed - RAMBUS. Whilst DDR is an "open" standard, meaning any manufacturer can implement it as they wish, providing it complies with the standard, RAMBUS is a proprietary technology.

DDR technology has almost reached the end of its lifecycle, insofar as technological development is concerned. Because DDR is tied into the system clock speed, it can only run as fast as the system bus.

Buses: PCI and AGP 1 Upgrading, Troubleshooting, and Common Problems