The undocumented PC

You will find each major subsystem of the PC explained in detail,
followed by extensive reference sections that show and explain both
documented and undocumented BIOS functions. Going into a level of
detail available nowhere else, The Undocumented PC covers all
the major system architectures and is still the only available
reference to input/output ports, undocumented CPU instructions, fixed
memory areas, and much more.

The bonus disk includes:

• diagnostic and analytical tools, including TSRs that monitor
  current I/O and serial port status on screen
  
• equipment detection routines for the disk, diskette, PCI, video,
  and other important aspects
  
• CPU detection routines to identify the exact CPU, FPU, speed,
  vendor, and other critical processor information, including the
  presence of MMX, and identify the true instruction set (it's often
  different from what you expect!)
  
• utilities to identify and test undocumented CPU instructions
  
• a Model Specific Register program that describes many
  undocumented registers by name and provides quick access to hidden
  registers
  
• demonstration utilities to access CMOS memory, the keyboard
  controller, and other subsystems
  

  Plus you get complete, documented source code for all utilities on
  the disk, including tools and utilities for diagnositc and analytic routines!
  

Frank van Gilluwe is President of V Communications, Inc., developers
of DOS and Windows programming tools, including the bestselling
Sourcer disassembler.