Welcome to the Unix Tree. Here you can browse the source code and manuals of various old versions of Unix. For every file, you can also find related files from other versions: this can help show how the different versions of Unix are related. Most of the Unix versions below come from the Unix Archive.

Image: Dennis Ritchie and Ken Thompson at a pretty well maxed out DEC PDP11 computer and two Teletype model 33 terminals. PanelSwitchman at Flickr. CC BY-NC-ND 2.0