Virtualisation:

  Virtual memory allows multiple programs running at the same
  time to store their variables (and everything else) in the
  same memory locations. One single real shared computer becomes
  a virtual private computer for each of its users.

  Time-sharing to allow multiple programs to run at the same
  time even when we haven't got a multi-core CPU has a similar
  effect.

  Data can only be accessed from disc in whole blocks at a time,
  each block is described by four numbers: disc drive number,
  surface number, track number and surface number (or as IBM
  called them cylinder, head, and surface, CHS, the disc drive
  number is taken for granted). But the operating system makes
  all that seem to be a rational organised collection of files
  and directories or whatever length is desired, in all sorts
  of different formats.



This is the program that didn't behave.
I realise now that that is due to the summer upgrade of rabbit,
it is a security feature. If you can't predict where variables
are going to be, worms are much more difficult to craft. Programs
are now started with a (restrictedly) random initial value for
the stack pointer.

This was the program, but there isn't much point in it now.

#include <stdio.h>

int main()
{ int a, b;
  printf("value for a: ");
  scanf("%d", & a);
  printf("a is at %08X and contains %d\n", & a, a);
  printf("value for b: ");
  scanf("%d", & b);
  printf("a is at %08X and contains %d\n", & a, a); }