What is DIRECT MEMORY ACCESS (DMA)

                             DIRECT MEMORY ACCESS (DMA)

Do you know what DMA is or how does it work? .If no let’s find out then

Direct Memory Access is a feature that transfers the date

directly between the storage device and the main memory

without the involvement of the CPU.

There are 3 parts in the system I/O peripheral (device), CPU and memory.

What happens is, when I/O device wants to send or store any data into memory it has to first intimate the CPU and then the CPU transfers the data to memory, it takes 2 cycles to complete this process i.e. I/O device to CPU 1 cycle and CPU to memory 1 cycle which consumes a lot of time.

But we can reduce the number of cycle to 1 by using DMA, which transfers the data from the I/O device to memory at a faster rate without involving the CPU.

Operations:-

1. When the device wants to transfer data to memory it has to first send a DMA request to the DMA controller.

2. DMA controller then requests CPU to hand over the operations to it; after CPU transfers the control to DMA controller it becomes the master.

3. Now DMA controller has the access to system bus, system bus contains data bus, address bus and control bus which are used to carry out the operations.

4. After the transferring to data is done to/from the memory the bus signal issues an interrupt, which means that the DMA controller is free to carry out the next operation.

Note: - Interrupt is nothing but it is a hardware signal to the processor that the I/O device is ready now and it can carry out another transfer of data

                                    

                                             -Sanket Mungarwadi