The main memory refers to the physical memory that is internal to the computer. The main word is used to distinguish it from external mass storage devices such as disk drives. Other terms used to mean main memory include RAM and main storage. The computer can only manipulate the data that is in the main memory. Therefore, every program that you run and each file that you access must be copied from a storage device to the main memory. The amount of main memory on a computer is crucial because it determines the number of programs that can be run at a time and the amount of data that can be easily accessed by a program.
As computers frequently have too slight main memory to hold all the data they need, computer engineers have invented a technique called interchange, in which portions of data are copied to main memory as they are needed. The exchange occurs when there is no room in the memory for the necessary data. When a portion of data is copied into the memory, a portion of equal size is copied (swapped) to make room.
Primary storage, also called primary storage or memory, is the area of a computer in which data is stored for quick access by the computer’s processor. The terms random access memory (RAM) and memory are often synonymous for primary or primary storage. Primary storage is volatile and can be compared to non-volatile secondary storage, also known as auxiliary storage. The terms primary storage and auxiliary storage came from the days of the central computer to distinguish the more immediately accessible data storage from the data stored on punch cards that required I / O operations. In the days when the mainframe data storage contained ferrite cores, the term base storage was often used instead of the main storage. Main memory resides in the middle of CPU and secondary memory after cache memory.
The primary storage of the label is often used to describe the storage for the data that is in use, as opposed to the data at rest in a backup. In this use, the main storage of the label may in fact describe the nonvolatile secondary storage referred to in sense above. It should be noted that, although these two meanings are in conflict, the appropriate meaning is usually apparent in the context. For example, the primary storage in a tiered storage architecture might be hard disks or flash-based SSDs on a centralized storage area network (SAN) or a network-attached storage (NAS) that stores transaction data or mission critical application data requiring extremely high performance.