Ever wondered what is really using up your PC's memory? Why does your
favourite program refuse to load after you added that last resident program?
Has that TSR you wrote really hooked to interrupt 09 correctly?
  To answer these questions, run DOSMAP. This program provides complete
information about the contents of your PC's memory - what programs are in
there, what memory they occupy and which interrupts they have taken over.
  Real hackers should use the -f (full) flag:
      DOSMAP -f
to see the most complete map of PC memory contents offered by any program,
PD, shareware or commercial.
  Unlike some other memory-map programs, DOSMAP gives correct results when
run in a subshell created by DOS or by a program, and when spawned in a 
child process. 


Abbreviations in DOSMAP -f output:

MCB - memory control block
ENV - environment block
PSP - program segment prefix