Question

Let's say I have the executable hello which prints hello world to the screen, and I run it by typing the name of the executable into the shell and then press enter. How does this work given a system's hardware organization?

Answer 1

Running an executable involves the shell locating, loading, and executing the program. The CPU processes the instructions, with the operating system managing the execution flow. The output 'hello world' is displayed through a system call to an output device.

Step-by-step explanation:

When you run an executable like hello which prints hello world on your screen, several steps are followed involving both software and hardware components. Initially, the shell interprets the command you have typed. When you press enter, the shell searches for the hello executable in your current directory or in the directories listed in the PATH environment variable. Once found, the shell loads the executable into memory.

The central processing unit (CPU) then fetches the instructions from memory, decodes them, and executes them. This process is significantly managed by the operating system which transfers control to the program, allowing it to run. During execution, the hello program invokes a system call that sends the text hello world to your output device, usually a terminal or console, displaying the message.

This is a simplified view of a complex interaction of system hardware and software that includes processors, memory, input/output devices, and system buses, all orchestrated by the operating system. Historical bulletin board systems like those from the 1980s, while much simpler by today's standards, followed similar principles to execute programs and display text.