Storage is one of the basic functions of any information processing system. Data and information need to be stored after input, during processing, and before needed as output. .
Primary Storage Areas.
The primary storage unit can be conceptually subdivided into input storage, output storage, program or instruction storage, and working storage. Storage receives data from input devices, program storage contains program instructions, and output storage contains information waiting for transfer to output devices. Working storage holds information being processed, as well as intermediate processing results. The primary storage units of many larger computers also include a small, very high-speed buffer or cache storage area. It is sometimes called scratch pad memory, because it is used to temporarily store data, instructions, and intermediate results during processing.
Arithmetic-Logic and Control Storage Areas.
Other categories of CPU storage include local storage, which consists of the high-speed registers of the arithmetic-logic unit, and control storage, which consists of the registers and read only storage area of the control unit. The registers are small high-speed storage circuits areas used for the temporary storage of an individual instruction or data element during the operation of the control and arithmetic-logic units. General-purpose registers carry out a variety of register functions, while special-purpose registers perform specific functions. For example, a storage register temporarily holds data or instructions taken from or being sent to primary storage. An address register may hold the address of the storage location of data, or the address of an input/output device or a control function. An instruction register contains the instruction being executed by the CPU. An accumulator register accumulates the results of arithmetic operations.
The CPUs of most computers today contain special storage circuitry modules where certain programs (software) are permanently stored in semiconductor ROM chips (hardware).