main memory

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main memory

computer technology

Also known as: primary memory

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June 30, 2026

Quick Summary

RAM, or random-access memory, is the main memory in a computer where the central processing unit (CPU) can directly read and write data quickly. This allows for rapid access to information regardless of where it's stored.12

There are two main types of RAM:
* Static RAM (SRAM): This type is very fast but physically larger and more expensive. It's typically used for small amounts of memory like CPU registers and cache memory. SRAM retains data as long as power is supplied.31
* Dynamic RAM (DRAM): This type is more common for main memory because it's denser and cheaper. DRAM stores data in capacitors that need to be refreshed periodically to retain information.13

Unlike ROM (read-only memory), RAM is volatile, meaning it loses its contents when the power is turned off.45

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cache memory
…an extension of, a computer’s main memory. Both main memory and cache are internal random-access memories (RAMs) that use semiconductor-based transistor circuits. Cache holds a copy of only the most frequently used information or program codes stored in the main memory. The smaller capacity of the cache reduces the time…
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…an extension of, a computer’s main memory. Both main memory and cache are internal random-access memories (RAMs) that use semiconductor-based transistor circuits. Cache holds a copy of only the most frequently used information or program codes stored in the main memory. The smaller capacity of the cache reduces the time…
Read More

computer memory
Main memory
The earliest memory devices were electro-mechanical switches, or relays (see computers: The first computer), and electron tubes (see computers: The first stored-program machines). In the late 1940s the first stored-program computers used ultrasonic waves in tubes of
Read More
The earliest memory devices were electro-mechanical switches, or relays (see computers: The first computer), and electron tubes (see computers: The first stored-program machines). In the late 1940s the first stored-program computers used ultrasonic waves in tubes of
Read More

computer
Main memory
The earliest forms of computer main memory were mercury delay lines, which were tubes of mercury that stored data as ultrasonic waves, and cathode-ray tubes, which stored data as charges on the tubes’ screens. The magnetic drum, invented about 1948, used an iron…
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The earliest forms of computer main memory were mercury delay lines, which were tubes of mercury that stored data as ultrasonic waves, and cathode-ray tubes, which stored data as charges on the tubes’ screens. The magnetic drum, invented about 1948, used an iron…
Read More

computer science
Algorithms and complexity
…from the fact that the main memory of a computer (where the data is stored) is linear, consisting of a sequence of memory cells that are serially numbered 0, 1, 2,…. Thus, the simplest data structure is a linear array, in which adjacent elements are numbered with consecutive integer “indexes”…
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…from the fact that the main memory of a computer (where the data is stored) is linear, consisting of a sequence of memory cells that are serially numbered 0, 1, 2,…. Thus, the simplest data structure is a linear array, in which adjacent elements are numbered with consecutive integer “indexes”…
Read More