Bus mastering
Busmastering , even bus mastering (English: bus mastering ) means that the processor of a computer system temporarily take control of the bus to an adapter card , called the bus master write. This bus master then independently addresses memory and I / O areas for the purpose of data transfer. The bus master operates as a kind of bridge or as an independent CPU. While such a secondary processor controls the peripheral bus, the CPU is able to carry out other work in the system, provided the necessary resources are available. Most of the time, the bus to the memory is still partially usable, there is time sharing. In modern multitasking operating systems in particular, this has a positive effect on the ability to react, with bus master activity often being linked to the operating system via an interrupt signal. The purpose of the adapter card is to serve certain tasks asynchronously to other tasks.
There are, for example, PCI bus masters and AGP bus masters. Typical representatives are network adapters , hard disk controllers , sound cards , video frame grabbers and graphics cards , which can have bus master capability. The data transfers take place between card and main memory, but also between card and card. More exotic representatives are crypto hardware or co-processors , so-called transputer boards.
The state that the CPU assumes during DMA transfers is largely comparable to that of a bus master, so that one often speaks of DMA bus master transfer, even if it is rather misleading.