In a disk drive with an AT interface, data transfers between the drive and host using programmed I/O (PIO). The host uses PIO to write to the Command Block Registers (CBRs) when transmitting control information, such as the location of a read command.

A data transfer method where the data is read or written by the CPU.

A standard method of accessing an I/O device - the CPU reads each byte of data from or writes each byte of data to the device.