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

Multiprogramming will be extremely difficult to be achieved.

Explanation:

If every byte of data read or written is handled by the CPU the implications this will have for multiprogramming are not going to be satisfactory.

This is because, unlike before, after the successful completion of the input and output process, the CPU of a computer is not entirely free to work on other instructions or processes.