System Unit Variables and Typed Constants (protected and real)

  Variable  │ Type            │ Description
 ═══════════╪═════════════════╪════════════════════════════════════
  Input     │ Text            │ Input standard file
  Output    │ Text            │ Output standard file

                      │Initial│
  Variable  │ Type    │ Value │ Description
 ═══════════╪═════════╪═══════╪════════════════════════════════
  ErrorAddr │ Pointer │   nil │ Run-time error address
  ExitCode  │ Integer │     0 │ Exit code
  ExitProc  │ Pointer │   nil │ Exit procedure
  FileMode  │ Byte    │     2 │ File open mode
  FreeList  │ Pointer │   nil │ Free heap list
  HeapEnd   │ Pointer │   nil │ Heap end
  HeapError │ Word    │   nil │ Heap error function
  HeapOrg   │ Pointer │   nil │ Heap origin
  HeapPtr   │ Pointer │   nil │ Heap pointer
  HInstance │ Word    │     0 │ Handle of this instance
  InOutRes  │ Integer │     0 │ I/O result buffer
  PrefixSeg │ Word    │     0 │ Program segment prefix (PSP)
  RandSeed  │ LongInt │     0 │ Random seed
  StackLimit│ Word    │     0 │ Minimum stack pointer
  Test8087  │ Byte    │     0 │ Result of 8087 test

   overlay typed constants   
   interrupt vector constants