What is the input output subsystem?

Answer 1

It is the specific layer of the operating system responsible for translating hardware and software inputs, such as keyboard and mouse event data, into data the application can use, and translating application output into hardware and software outputs, such as the screen or a printer. This layer of abstraction allows the program and various inputs and outputs to be decoupled.

For example, in a terminal program, output is normally sent to the screen, but can be redirected to a file, printer, a network socket, or even another program, without the program needing any special consideration as to how to write this data to various outputs. Also, most terminal programs expect input from the keyboard, but this input can similarly be fed from any valid source (e.g. any source that has an output to connect to an input).