DMA (Direct Memory Access)

DMA (Direct Memory Access): is a procedure for transferring data directly between controller and memory without the help of CPU.

DMA device: is like a separate CPU with functions related to data transfer, such as:

–          shuts the CPU down for short periods

–          seizes control of the system bus

–          transfers data between memory and external device without the intermediation of CPU

Disk controller: accepts commands from CPU such as:

–          select disk drive

–          set up DMA registers

–          return current sector address

–          return current track address

–          move head in/out one track

–          move head to track 0

–          read/write current sector

Status port: contains the result of a query from CPU or status

Control port: commands for the controller are placed

DMA address registers: they receive addresses from CPU