4.5   THE INPUT/OUTPUT SUBSYSTEM

Input and output (I/O) devices allow us to communicate with the computer system. I/O is the transfer of data between primary memory and various I/O peripherals. Input devices such as keyboards, mice, card readers, scanners, voice recognition systems, and touch screens enable us to enter data into the computer. Output devices such as monitors, printers, plotters, and speakers allow us to get information from the computer.

These devices are not connected directly to the CPU. Instead, there is an interface that handles the data transfers. This interface converts the system bus signals to and from a format that is acceptable to the given device. The CPU communicates to these external devices via I/O registers. ...

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