Register is a word with several meanings: as a noun it refers to the actual book in which you record things, like your car registration or your class schedule. As a verb it can mean to sign up officially or to mark something clearly, as in the case of registering your vote or registering for classes. It can also refer to the range of sound your voice or instrument can make, as in the upper register of a clarinet. Register can also refer to a place or system for recording things, such as a cash register in a retail environment, or it can refer to an official list, such as a register of deeds or an electoral roll.
A CPU register is a small but very fast storage memory within the central processing unit (CPU) or the arithmetic logic unit (ALU). Registers are used for a variety of functions in handling and controlling instructions and data, and play an important role in improving CPU performance and efficiency.
Registers provide temporary storage of data for immediate processing by the CPU during arithmetic and logic operations. They also store data and return addresses during function calls. As a result, registers can eliminate the need to access slower main memory frequently – thereby enhancing processor performance and efficiency.
Most modern CPUs use registers to implement instruction fetching, decoding, and execution. During the fetching stage, the computer determines the next set of instructions to process. Then, the computer fetches those instructions from memory. It then decodes them, determining the types of operations they require. Finally, the computer executes those instructions – performing calculations, transferring data from one location to another, or accomplishing any other type of operation specified in the instructions.
In general, the registers are used to store bits of information that are being manipulated or tested by machine instructions. Almost all computers, whether they have a load/store architecture or not, load items of data from a larger memory into the registers for arithmetic operations and other tests. After the results of these manipulations are retrieved from the registers, they can either be stored back to main memory or used by a subsequent instruction.
The registers are a critical part of the processor because they enable quick and efficient data manipulation, reducing the need for frequent access to slower main memory – thus boosting CPU performance and efficiency. The cost of the registers, however, is a significant factor in determining the overall price of a CPU.
In addition to the registers, most modern CPUs have several levels of memory hierarchy with varying speeds and capacities. They also have multiple caches to improve memory access.