Dynamic random-access memory: Difference between revisions

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[[Image:MT4C1024-HD.jpg|thumb|right|upright=1.84|thumb|A [[Die (integrated circuit)|die]] photograph of the [[Micron Technology]] MT4C1024 DRAM [[integrated circuit]] (1994). It has a capacity of 1&nbsp;[[megabit]] equivalent to <math>2^{20}</math>bits or {{nowrap|128 [[KiB]].}}<ref name=mt4acid>{{cite web |access-date=2016-04-02 |date=2012-11-15 |title=How to "open" microchip and what's inside? : ZeptoBars |url=http://zeptobars.com/en/read/how-to-open-microchip-asic-what-inside |quote=Micron MT4C1024 — 1 mebibit (220 bit) dynamic ram. Widely used in 286 and 386-era computers, early 90s. Die size - 8662x3969μm. |url-status=live |archive-url=https://web.archive.org/web/20160314015357/http://zeptobars.com/en/read/how-to-open-microchip-asic-what-inside |archive-date=2016-03-14 }}</ref>]]

{{Memory types}}

[[Image:MT4C1024-HD.jpg|thumb|right|upright=1.8|A [[Die (integrated circuit)|die]] photograph of the [[Micron Technology]] MT4C1024 DRAM [[integrated circuit]] (1994). It has a capacity of 1&nbsp;[[megabit]] equivalent to <math>2^{20}</math>bits or {{nowrap|128 [[KiB]].}}<ref name=mt4acid>{{cite web |access-date=2016-04-02 |date=2012-11-15 |title=How to "open" microchip and what's inside? : ZeptoBars |url=http://zeptobars.com/en/read/how-to-open-microchip-asic-what-inside |quote=Micron MT4C1024 — 1 mebibit (220 bit) dynamic ram. Widely used in 286 and 386-era computers, early 90s. Die size - 8662x3969μm. |url-status=live |archive-url=https://web.archive.org/web/20160314015357/http://zeptobars.com/en/read/how-to-open-microchip-asic-what-inside |archive-date=2016-03-14 }}</ref>]]

[[File:NeXTcube motherboard.jpg|thumb|[[Motherboard]] of the [[NeXTcube]] computer, 1990, with 64 MiB main memory DRAM (top left) and 256 KiB of [[Video RAM (dual-ported DRAM)|VRAM]]<ref>{{cite web|url=http://www.nextcomputers.org/NeXTfiles/Docs/Hardware/NeXTServiceManualPages1-160_OCR.pdf |title=NeXTServiceManualPages1-160 |date= |access-date=2022-03-09}}</ref> (lower edge, right of middle)]]

'''Dynamic random-access memory''' ('''dynamic RAM''' or '''DRAM''') is a type of [[random-access memory|random-access]] [[semiconductor memory]] that stores each [[bit]] of data in a [[memory cell (computing)|memory cell]], usually consisting of a tiny [[capacitor]] and a [[transistor]], both typically based on [[metal–oxide–semiconductor]] (MOS) technology. While most DRAM memory cell designs use a capacitor and transistor, some only use two transistors. In the designs where a capacitor is used, the capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The [[electric charge]] on the capacitors gradually leaks away; without intervention the data on the capacitor would soon be lost. To prevent this, DRAM requires an external [[memory refresh]] circuit which periodically rewrites the data in the capacitors, restoring them to their original charge. This refresh process is the defining characteristic of dynamic random-access memory, in contrast to [[static random-access memory]] (SRAM) which does not require data to be refreshed. Unlike [[flash memory]], DRAM is [[volatile memory]] (vs. [[non-volatile memory]]), since it loses its data quickly when power is removed. However, DRAM does exhibit limited [[data remanence]].

'''Dynamic random-access memory''' ('''dynamic RAM''' or '''DRAM''') is a type of [[random-access memory|random-access]] [[semiconductor memory]] that stores each [[bit]] of data in a [[memory cell (computing)|memory cell]], usually consisting of a tiny [[capacitor]] and a [[transistor]], both typically based on [[metal–oxide–semiconductor]] (MOS) technology. While most DRAM memory cell designs use a capacitor and transistor, some only use two transistors. In the designs where a capacitor is used, the capacitor can either be charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The [[electric charge]] on the capacitors gradually leaks away; without intervention the data on the capacitor would soon be lost. To prevent this, DRAM requires an external [[memory refresh]] circuit which periodically rewrites the data in the capacitors, restoring them to their original charge. This refresh process is the defining characteristic of dynamic random-access memory, in contrast to [[static random-access memory]] (SRAM) which does not require data to be refreshed. Unlike [[flash memory]], DRAM is [[volatile memory]] (vs. [[non-volatile memory]]), since it loses its data quickly when power is removed. However, DRAM does exhibit limited [[data remanence]].

DRAM typically takes the form of an [[integrated circuit]] chip, which can consist of dozens to billions of DRAM memory cells. DRAM chips are widely used in [[digital electronics]] where low-cost and high-capacity [[computer memory]] is required. One of the largest applications for DRAM is the ''[[main memory]]'' (colloquially called the RAM) in modern [[computer]]s and [[graphics card]]s (where the main memory is called the ''[[Video random access memory|graphics memory]]''). It is also used in many portable devices and [[video game]] consoles. In contrast, SRAM, which is faster and more expensive than DRAM, is typically used where speed is of greater concern than cost and size, such as the [[CPU cache|cache memories]] in [[Central processing unit|processor]]s.