Long description

The figure consists of four blocks labeled C P U, D M A controller, Disk controller, and main memory connected from the bottom by a bus. The D M A controller block contains three sub-blocks labeled address, count, and control. An arrow labeled 1, C P U programs the D M A controller from C P U block points to the D M A controller block. Another arrow labeled 2, D M A requests transfer to memory points from D M A controller to the disk controller block. The disk controller contains a block labeled buffer which is connected to the main memory block using an arrow labeled 3, data transfer. A drive is also attached to the disk controller. An arrow from the disk controller points to the D M A controller labeled 4, Ack. Another arrow from the D M A controller points to the C P U labeled interrupt when done.