The Register Model

RISC or CISC machine registers are actually the processor's 'fastest' memory. This memory resides directly on your processor. They're designed to be short-term memory locations that can hold addresses, data, or instructions. The idea is that there is little or no latency when pulling information from the register. Latency simply refers to the delay or lag time when seeking out or returning information.

Registers as Storage Locations

Registers are used for is also a temporary storage location for a value. For example, say that you were going to multiply a table of numbers by a constant. If the constant is placed in the register, every time you fetch one of the numbers in the table, the processor simply pulls the constant from the register quickly and completes the calculation in the quickest amount of time.

Registers Help to Expose the Parallelism

Any microprocessor needs more registers to expose more parallelism in the code. In a typical enterprise-computing environment, where we want to execute multiple instructions at a time and take advantage of parallel operations, there is a need to keep track of “all of the balls in the air”. To keep track of these “balls in the air” requires more registers, or at least more register names. More registers enable a wider issue machine (Itanium processors can issue 6 instructions per cycle), and allow a deeper pipeline to get more things done in parallel.