General-purpose registers can be assigned to a variety of functions by the programmer. In some cases, general- purpose registers can be used for addressing functions (e.g., register indirect, displacement).

In other cases, there is a partial or clean separation between data registers and address registers.

Data registers may be used to hold only data and cannot be employed in the calculation of an operand address.

Address registers may be somewhat general purpose, or they may be devoted to a particular addressing mode. Examples include the following:

• Segment pointer: In a machine with segment addressing, a segment register holds the address of the base of the segment. There may be multiple registers, one for the code segment and one for the data segment.
  
• Index registers: These are used for indexed addressing and may be autoindexed.
  
• Stack pointer: If there is user visible stack addressing, then typically the stack is in memory and there is a dedicated register that points to the top of the stack.

Condition Codes (also referred to as flags) are bits set by the CPU hardware as the result of the operations. For example, an arithmatic operation may produce a positive, negative, zero or overflow result. In addition to the result itself beign stored in a register or memory, a condition code is also set. The code may be subsequently be tested as part of a condition branch operation. Condition code bits are collected into one or more registers.