The use of bus master adapters avoids the need for the system processor to become involved in data transfers between adapters in the system. For example, a bus master LAN adapter may interact with the disk subsystem to service I/O requests on a LAN server, while the system processor continues to process other work.
Bus master adapters provide advantages over other "intelligent" adapters such as DMA adapters, since a bus master is typically directly involved in the data transfer (as either source or destination) and thus requires only a single operation to transfer the data, while a DMA adapter requires two (one read and one write). In addition, the DMA controller used in current IBM PS/2 system units is only capable of 24-bit addressing, while bus master adapters, such as the SCSI adapters, utilize the full 32-bits available on the address bus on the PS/2 models 90 and 95.
A bus master may randomly address memory and memory-mapped I/O devices. This makes it ideal for paged environments and enables the bus master to execute chains of work, addressing different memory areas and devices without support from the system processor. The bus master adapter is regarded as a subsystem and can work completely asynchronously to the system processor and other bus masters. Where necessary a bus master may communicate directly with another bus master.