DIRECT MEMORY ACCESS

IN a computer the CPU, Memory and DMA controller are the central units to which other
peripheral subsystems like input/output controllers are interfaced.

The type of information(signals) flow between the cpu and the memory are the following:-

1.Data signals :> This includes instruction and data .

2.Address signals :> This is memory address or peripheral address.

3.Control signals :> This includes signals like memory write, memory read,I/O write,I/O read interrupt , reset.



For each type of signal or communication there is one path or bus ;-

1. Data Bus :> The data bus is used when any unit is sending data,instruction or command
code to some other unit.

2. Address Bus :> The address bus is used when one unit is sending address information to
another unit.

3. Control Bus :> The control bus is used when one unit is sending a control signal to
another unit.


Bus Arbitration :> Usually , the cpu is the bus master in a computer.It decides who should
access or control the bus when more than one unit wants the bus at the
same time.This is known as Bus Arbitration.

An unit who needs the bus makes a request to the CPU and awaits sanction.Till the CPU issue
sanction the requesting unit does not attempt to use the bus.In a PC apart from the CPU
only the DMA controller controls the bus.