What does it mean to speak to a computer? The idea of input has meant different things over time, changing as technological complexity has evolved. Early computing services were highly constrained, allowing for only simple, codified inputs that told the computer to run one program or another, requiring high user knowledge and technical skill.
The origins of inputs lie in the early days of computing. In the 1960s, a group of researchers at MIT developed a time-sharing operating system called Multics (Multiplexed Information and Computing Service). This experimental platform introduced many of the concepts we now take for granted in modern computing, such as hierarchical filesystems, dynamic linking, and virtual memory. But with regard to this chapter, its most important contribution was something simpler: the command shell. Figure 3-1 shows Multics in action.
A command shell is a text-based interface where users type instructions and the computer responds. When you type a command like ls or dir and hit Enter, the shell interprets that text, executes the corresponding program, and displays the results underneath. It acts as an interpreter between human language and machine operations, taking typed commands, figuring out what program you want to run, and then showing you what happened. If you’ve ever opened Terminal on a Mac (see Figure 3-2) or Command Prompt on Windows, you’ve seen a modern version of the command shell.
Figure 3-1. The command ...
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