bus master
A bus master is the program, either in a microprocessor or more usually in a separate I/O controller, that directs traffic on the computer bus or input/output paths. The bus master is the "master" and the I/O devices on the bus are the "slaves." The bus master actually controls the bus paths on which the address and control signals flow. Once these are set up, the flow of data bits goes directly between the I/O device and the microprocessor.