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"Hello, World!" program handwritten in the C language and signed by Brian Kernighan (1978)
(upload.wikimedia.org)
A "Hello, World!" program is generally a simple computer program which outputs (or displays) to the screen (often the console) a message similar to "Hello, World!" while ignoring any user input. A small piece of code in most general-purpose programming languages, this program is used to illustrate a language's basic syntax.
A "Hello, World!" program is often the first written by a student of a new programming language, but such a program can also be used as a sanity check to ensure that the computer software intended to compile or run source code is correctly installed, and that its operator understands how to use it.
I was tempted to put this in ~~r/history~~ c/history.
Ninja edit: Where is my mind?