Primary
Memory ○｜Definition｜1st｜20251119205401-00-⌔
Computer memory
Computer memory stores information, such as data and programs, for immediate use in the computer;1 instructions fetched by the computer, and data fetched and stored by those instructions, are located in computer memory. The terms memory, main memory, and primary storage are also used for computer memory.
Computer memory is often referred to as RAM, meaning random-access memory, although some older forms of computer memory, such as drum memory, are not random-access. Archaic synonyms for main memory include core (for magnetic-core memory) and store.2
Main memory operates at a high speed compared to mass storage which is slower but less expensive per bit and higher in capacity. Besides storing opened programs and data being actively processed, computer memory serves as a mass storage cache and write buffer to improve both reading and writing performance. Operating systems typically borrow RAM capacity for caching so long as it is not needed by running software.3 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,45 where data is stored within memory cells built from MOS transistors and other components on an integrated circuit.6 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 mainly 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 a 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 2 words in the memory.
Printed 2026-06-28.
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Link to original Footnotes
Hemmendinger, David (February 15, 2016). “Computer memory”. Encyclopedia Britannica. Retrieved 16 October 2019. ↩
A.M. Turing; R.A. Brooker (1952). “1. General remarks on electronic computers”. Programmer’s Handbook for Manchester Electronic Computer Mark II. University of Manchester. Archived from the original on 2014-01-02. ↩
“Documentation for/proc/sys/vm/”. ↩
“The MOS Memory Market” (PDF). Integrated Circuit Engineering Corporation. Smithsonian Institution. 1997. Archived (PDF) from the original on 2003-07-25. Retrieved 16 October 2019. ↩
“MOS Memory Market Trends” (PDF). Integrated Circuit Engineering Corporation. Smithsonian Institution. 1998. Archived (PDF) from the original on 2019-10-16. Retrieved 16 October 2019. ↩
“1960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated”. The Silicon Engine. Computer History Museum. ↩
Secondary
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