Q: Where can I find the historical source code of the Linux sources I want to do research on the evolution of Linux.
Therefore it would be nice if I could download the sources of Linux at several moments in time (from 1991 till now).
Is there a site where one can find those sources?
Similar sites for other Unix based operating systems are also welcome.

A: Check this URL: http://www.kernel.org/pub/linux/kernel/

A: Archive.org hosts a Git repo with the complete history of Linux, made by grafting 3 repositories together.  You'd probably need to do a git pull to update it with the most recent changes.

A: The Unix Heritage Society has a load of old Genuine Unix source code. The source code page has Bell Labs Unix from Version 1 through 6, 32V, System III, some or all of the BSDs, pointers to Linux progenitor Minix.

A: I suggest these two: 
http://www.oldlinux.org/
and a more straightforward one from this site that contain Linux kernel 0.01, 0.10, 0.11,...,0.98: 
http://www.oldlinux.org/Linux.old/
and the other:
http://www.codeforge.com/article/170371
