memory mapped I/O

memory mapped I/O

(architecture)The use of the same instructions and bus tocommunicate with both main memory and input/outputdevices. This is in contrast to processors that have aseparate I/O bus and special instructions to access it.

The I/O devices are addressed at certain reserved addressranges on the main memory bus. These addresses cannottherefore be used for RAM. Motorola and Mostecarchitectures, among others, use memory mapped I/O.

Video cards and other cards with on-board memory might beaccessed in this way though the term applies not just todevices containing memory but to any device connected to thememory bus. Accessing the devices usually consists of readingand writing certain built-in registers though sometimes themere presence of a particular address can trigger the device.