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Computer memory

Component of a computer storing information for immediate use. / From Wikipedia, the free encyclopedia

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Computer memory stores information, such as data and programs for immediate use in the computer.[2] The term memory is often synonymous with the term primary storage or main memory. An archaic synonym for memory is store.[3]

DDR4 SDRAM module. As of 2021, over 90 percent of computer memory used in PCs and servers was of this type.[1]

Computer memory operates at a high speed compared to storage which is slower but less expensive and higher in capacity. Besides storing opened programs, computer memory serves as disk cache and write buffer to improve both reading and writing performance. Operating systems borrow RAM capacity for caching so long as not needed by running software.[4] If needed, contents of the computer memory can be transferred to storage; a common way of doing this is through a memory management technique called virtual memory.

Modern computer memory is implemented as semiconductor memory,[5][6] where data is stored within memory cells built from MOS transistors and other components on an integrated circuit.[7] There are two main kinds of semiconductor memory: volatile and non-volatile. Examples of non-volatile memory are flash memory and ROM, PROM, EPROM and EEPROM memory. Examples of volatile memory are dynamic random-access memory (DRAM) used for primary storage, and static random-access memory (SRAM) used for CPU cache.

Most semiconductor memory is organized into memory cells each storing one bit (0 or 1). Flash memory organization includes both one bit per memory cell and multi-level cell capable of storing multiple bits per cell. The memory cells are grouped into words of fixed word length, for example, 1, 2, 4, 8, 16, 32, 64 or 128 bits. Each word can be accessed by a binary address of N bits, making it possible to store 2N words in the memory.