Linux.com
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A Linux portal and directory.
http://www.linux.com/
Microsoft Corp.: Windows
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Official Windows product line root page.
http://www.microsoft.com/windows/
Convergence International
The non-Wintel user group, supporting Acorn, Amiga, Apple, ARM, Be, NCs, PowerPC, Psion, Unix and other alternative operating systems. Services include a non-Wintel news summary.
http://www.convergence.org/
Internet Operating System Counter
Statistics on Internet OS use, WWW, FTP, and News servers. Over 940,000 hosts checked in this 1999 survey.
http://www.leb.net/hzo/ioscount/
Linux Kernel Architecture and Other OS Links
Categorized, large link list of resources on several operating systems: Linux, Windows, BSD, Mac OS X, Unix, Solaris, Palm OS, Symbian, Stinger (SmartPhone), general.
http://cs.uml.edu/~cgould/