The device in your PC that controls the bus. Normally, this would be the processor, but in high-performance computers the video adapter or disk controller can take control of the bus to allow it to exchange data very rapidly with the main memory. It's a way of moving data to and from main memory without troubling the processor. If your PC has a bus master graphics card, then it will transfer data and draw images on screen faster than normal. Only some PCs can support bus master devices. If your PC has an EISA or MCA bus then it can support bus mastering. If it has an ISA - sometimes called an AT - bus, then it cannot. Local bus uses a form of bus mastering, but it's not really the same thing.