Andrew S. Tanenbaum (OS) Edition 4 Exercise 1 Question 5 (Page No. 81)

Question

On early computers, every byte of data read or written was handled by the CPU (i.e., there was no DMA). What implications does this have for multiprogramming?

Answer 1

The main reason for providing DMA is to give the CPU flexibility to perform any other task while the I/O is being performed by CPU. 

If there is no DMA in the multiprogramming system then the CPU will be fully occupied by the I/O devices, eventually leading no advantage of having a multiprogramming system benefit.

Comments

Yeah. By the way, multiprogramming is still possible without DMA but it will be very slow because of I/O interrupts.

Read it more.

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Yes, right.

Answer 2

1)The main thing is that the the I/O operations will be very slow.

2)In case if a data block is to be transferred to main memory , data block first gets transferred to cpu which then transfers the data to the main memory .This process is extremely slow and will increase the overall time  required by processes.