An anonymous reader writes "As part of his 1680-page book Mac OS X Internals: A Systems Approach, Amit Singh of kernelthread.com wrote a very detailed technical history of Apple's operating systems. Since he had to cut down on the history chapter because of the book's already too-large size, most of this chapter didn't make it to the printed book. Singh has made available the history chapter as a free PDF. The file is 140 pages long, and is generously filled with figures and screenshots. It starts with the internals of the original Apple I and goes through a tour of all operating systems Apple dabbled with, including internals of A/UX, Lisa OS, and such. It even covers details of outside influences like the Xerox Alto, STAR System, Smalltalk, and Sketchpad, and closer to home things like Mach, NeXTStep, and OpenStep."