What is meant by PIO, DMA, and Bus Master DMA?
PIO stands for Programmed (or Polled) Input/Output. This means that the CPU is used to read and write data directly to and from the host adapter chips. This is typically only used on low cost host adapter cards because it ties up the CPU during I/O which makes multi-tasking work poorly. DMA, or Direct Memory Access means exactly that. Special circuitry is included either on the motherboard, or the host adapter card itself, that can move data between system memory and the host adapter, with the CPU only performing a simple initial setup of the transfer. There are two distinct types of DMA circuitry used in PCs, third-party DMA and Bus Mastering DMA. Third-party DMA uses chips built into all PC/AT compatible motherboards to transfer the data. Bus Mastering DMA uses circuitry on the host adapter card itself to take control of the bus and transfer the data. PCI host adapters all use Bus Mastering DMA. This is the most efficient of the three data transfer methods and consequently also the m