Programming Fundamentals/Input and Output

Overview

Input and output, or I/O are how an information processing system communicates with the outside world, a human, or another information processing system. Inputs are the signals or data received by the system and outputs are the signals or data sent from it.^[1]

Discussion

Every task done on the computer happens inside the central processing unit (CPU) and the associated memory. Once our program is loaded into memory and the operating system directs the CPU to start executing our programming statements the computer looks like this:

Our program, now loaded into memory, has basically two areas:

Machine instructions – our instructions for what we want done
Data storage – our variables that we're using in our program

Often our program contains instructions to interact with the input/output devices. We need to move data into (write) and/or out of (read) the memory data area. A device is a piece of equipment that is electronically connected to the memory so that data can be transferred between the memory and the device. Historically this was done with punched cards and printouts. Tape drives were used for electronic storage. With time we migrated to using disk drives for storage with keyboards and monitors (with monitor output called soft copy) replacing punch cards and printouts (called hard copy).

Most computer operating systems and by extension programming languages have identified the keyboard as the standard input device and the monitor as the standard output device. Often the keyboard and monitor are treated as the default device when no other specific device is indicated.