A major rewrite/reorganisation.
New material on bytecodes.
Deleted some of the really out of date stuff about the old system
 (You might have to checkout the previous revision if you need
  historical info.)
I have not merged the sections on TSOs and Stacks.
 SimonM has a clearer idea of what the TSO status words look like and
 I think he said he'd written a new section with stacks part of TSOs.