The Operating Systems Resource Center
Extensive information about booting, file systems, memory, architecture, and interfacing with other devices.

The OSKit Project
An open source set of libraries that can be used as building blocks for an operating system for x86. Includes documentation and publications.

Therx OS Development Library
A site containing archived documents relating to the programming of Operating Systems.

Tony Macs Programming Pages
Focuses on x86 programming and includes links to other good sites, including MenuetOS. Collectoin OS sreenshots.

Triada
Ukrainiann Operating System. OS sources, toolkit downloads. OS development related articles.

Tuomo Kortesmaa
Notes and example code for basic operating systems concepts, threads, sockets, and device drivers.

Virtual Memory Tutorial
Extensive discussion of virtual memory. You Would also find info related to interactive workbenches, CPU utilization, throughput, performance, space-time, stack algorithms, replacement policies and much more.

Write Your Own Operating System [FAQ]
The Hobbyist guide to writing your own operating system from the ground up, Question and Answer style on everything from PMode to filesystems to GCC and doing it in C++.

Xosdev OS Development Central
Directory of OS development related resources. You Would also find info related to OS, Operating System, PM, Protected Mode, Hardware, Reference, Manual, Tutorial, Book, Tools, CPU, Memory Management, PIT, PIC, Timer, Floppy, FDC, Keyboard, File System, FAT, MMU and much more.