Registers

Registers are fast Memory that are fetched. A processor register is a quickly accessible location available to a computer’s processor. Registers usually consist of a small amount of fast storage, although some registers have specific hardware functions, and may be read-only or write-only.

• CPU instructions:

  • read from memory

• MIPS has 32 registers that called “general purpose”

• ARM has 64 registers (I think)

• The registers hi and lo (for multiplication and division)

• Some general-purpose registers are special:

  • $0 is always 0
  • $31 is for return addresses
  • $30 is our stack pointer
  • $29 is our frame pointer

Two categories of visible registers:

• Data registers: store data
• Address register: point to memory

There are also invisible registers (Control and Status Registers):

• Program Counter for example
• Invisible to the user (on most architectures)
• Used by Processor to control operating of the computer
• Used by privileged OS routines to control the execution of programs

MIPS Instructions

Special register = Program Counter that fixes the problem of how MIPS know what to do next.

In Assembly language, registers have global scope.