User-Visible Register

Introduced to this through SE350.

Enable programmer to minimize main memory references by optimizing register use.

User-visible registers are available to all programs – application programs and system programs.

  • Depend on computer architecture
  • May be referenced by machine language
  • Usually the compiler controls them

Can be user controlled:

Two categories of visible registers:

  1. Data registers: store data (e.g., results from calculations; D0-D7 in M68k processors)
  2. Address register: point to memory
  • Indexed addressing (Adding an index to a base value to get the effective address)
  • Segment pointer (When memory is divided into segments, memory is referenced by a segment and an offset)
  • Stack pointer (Points to top of stack for pop & push)