Warning: Blatant advertisement follows

Ever wanted the full scoop on undocumented MSDOS calls?  Run to your
favorite bookstore and ask for

     Undocumented DOS:
       A Programmer's Guide to Reserved MS-DOS Functions and Data Structures
     Andrew Schulman, Raymond J. Michels, Jim Kyle, Tim Paterson, David
       Maxey, and Ralf Brown

     694+xviii pages, 7-3/8" x 9-1/8"
     Addison-Wesley
     ISBN 0-201-57064-5
     $39.95 (book and two 5.25" disks)
     Available now

Don't buy it for the Appendix derived from the Interrupt List, buy it for a
full hypertext version of INTER490, a script-based interrupt monitoring
utility, source for a sample network redirector, discussions of
TSRs/multitasking/networks/installable file systems/debugging, lots of
examples, etc.