Q. Programmed input - output technique for computers?

Programmed input/output is a useful I/O technique for computers where hardware costs need to be minimised. Input or output operation in these cases may involve:

a)  Transfer of data from I/O device to processor registers.

b)  Transfer of data from processor registers to memory.

With programmed I/O method responsibility of processor is to constantly check status of I/O device to check whether it's free or it has completed inputting data. So this method is quite time consuming where processor wastes so much time in checking and verifying status of an I/O device. Figure (a) gives an illustration of use of programmed I/O to read in a block of data from a peripheral device into memory.