Shared graphics memory

Shared graphics memory is a system design in which the graphics chip does not include dedicated memory, and instead may share the main system RAM with the CPU and other components. This design is used by many graphics cards to reduce cost and complexity, as no additional memory chips are required on the board. Some mechanism (via the BIOS or a jumper setting) to select the amount of system memory to use for graphics. The graphics system can be tailored to use only as much RAM as is required, leaving the rest free. A side effect of this is that when some RAM is allocated for graphics, it becomes unavailable for anything else, so an example computer with 512 MiB RAM set up with 64 MiB graphics RAM will appear to the operating system and user to only have 448 MiB RAM installed. The disadvantage of this design is lower performance because system RAM usually runs slower than dedicated graphics RAM. Sharing the memory bus increases contention. It may also cause performance issues with the rest of the system if it is not designed to operate with the remaining amount of RAM. A similar approach that gave similar results is used in some SGi computers, most notably the O2/O2+. The memory in t