Random-access memory: Difference between revisions

Revision as of 21:58, 31 May 2025

Revision as of 21:59, 11 June 2025

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==Types==

In general, the term ''RAM'' refers solely to solid-state memory devices, and more specifically the main memory in most computers. The two widely used forms of modern RAM are [[static RAM]] (SRAM) and [[dynamic RAM]] (DRAM). In SRAM, a [[Bit|bit of data]] is stored using the state of a [[Memory cell (computing)|memory cell]], typically using six MOSFETs. This form of RAM is more expensive to produce, but is generally faster and requires less static power than DRAM. In modern computers, SRAM is often used as [[CPU cache|cache memory for the CPU]]. DRAM stores a bit of data using a transistor and [[capacitor]] pair (typically a MOSFET and [[MOS capacitor]], respectively),<ref>{{cite book |last1=Sze |first1=Simon M. |author1-link=Simon Sze |title=Semiconductor Devices: Physics and Technology |date=2002 |publisher=[[Wiley (publisher)|Wiley]] |isbn=0-471-33372-7 |page=214 |edition=2nd |url=http://www.fulviofrisone.com/attachments/article/453/Semiconductor.Devices_Physics.Technology_Sze.2ndEd_Wiley_2002.pdf}}</ref> which together comprise a DRAM cell. The capacitor holds a high or low charge (1 or 0, respectively), and the transistor acts as a switch that lets the control circuitry on the chip read the capacitor's state of charge or change it. As this form of memory is less expensive to produce than static RAM, it is the predominant form of computer memory used in modern computers.<!--[[User:Kvng/RTH]]-->

Both static and dynamic RAM are considered ''volatile'', as their state is lost or reset when power is removed from the system. By contrast, [[read-only memory]] (ROM) stores data by permanently enabling or disabling selected transistors, such that the memory cannot be altered. Writable variants of ROM (such as [[EEPROM]] and [[NOR flash]]) share properties of both ROM and RAM, enabling data to [[Persistence (computer science)|persist]] without power and to be updated without requiring special equipment. [[ECC memory]] (which can be either SRAM or DRAM) includes special circuitry to detect and/or correct random faults (memory errors) in the stored data, using [[parity bit]]s or [[Error detection and correction#Error-correcting code|error correction codes]].

[[ECC memory]] (which can be either SRAM or DRAM) includes special circuitry to detect and/or correct random faults (memory errors) in the stored data, using [[parity bit]]s or [[Error detection and correction#Error-correcting code|error correction codes]].<!--[[User:Kvng/RTH]]-->

In general, the term ''RAM'' refers solely to solid-state memory devices (either DRAM or SRAM), and more specifically the main memory in most computers. In optical storage, the term [[DVD-RAM]] is somewhat of a misnomer since, it is not random access; it behaves much like a hard disc drive if somewhat slower. Aside, unlike [[CD-RW]] or [[DVD-RW]], DVD-RAM does not need to be erased before reuse.

==Memory cell==