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In [[computing]], a '''cache''' ({{IPAc-en|audio=LL-Q1860 (eng)-Back ache-cache.wav|k|æ|ʃ}} {{respell|KASH}})<ref>
{{cite web|url=http://www.oxforddictionaries.com/definition/english/cache|archive-url=https://web.archive.org/web/20120818122040/http://oxforddictionaries.com/definition/english/cache|url-status=dead|archive-date=18 August 2012|title=Cache|work=Oxford Dictionaries|access-date=2 August 2016}}</ref> is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere. A '''cache hit''' occurs when the requested data can be found in a cache, while a '''cache miss''' occurs when it cannot. Cache hits are served by reading data from the cache, which is faster than recomputing a result or reading from a slower data store; thus, the more requests that can be served from the cache, the faster the system performs.<ref>{{Cite journal|last1=Zhong|first1=Liang|last2=Zheng|first2=Xueqian|last3=Liu|first3=Yong|last4=Wang|first4=Mengting|last5=Cao|first5=Yang|date=February 2020|title=Cache hit ratio maximization in device-to-device communications overlaying cellular networks|url=http://dx.doi.org/10.23919/jcc.2020.02.018|journal=China Communications|volume=17|issue=2|pages=232–238|doi=10.23919/jcc.2020.02.018|s2cid=212649328|issn=1673-5447|url-access=subscription}}</ref>
To be cost-effective, caches must be relatively small. Nevertheless, caches are effective in many areas of computing because typical [[Application software|computer applications]] access data with a high degree of [[locality of reference]]. Such access patterns exhibit temporal locality, where data is requested that has been recently requested, and spatial locality, where data is requested that is stored near data that has already been requested.
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Earlier [[graphics processing unit]]s (GPUs) often had limited read-only [[texture cache]]s and used [[swizzling (computer graphics)|swizzling]] to improve 2D [[locality of reference]]. [[Cache miss]]es would drastically affect performance, e.g. if [[mipmapping]] was not used. Caching was important to leverage 32-bit (and wider) transfers for texture data that was often as little as 4 bits per pixel.
As GPUs advanced, supporting [[General-purpose computing on graphics processing units (software)|general-purpose computing on graphics processing units]] and [[compute kernel]]s, they have developed progressively larger and increasingly general caches, including [[instruction cache]]s for [[shader]]s, exhibiting functionality commonly found in CPU caches. These caches have grown to handle [[synchronization primitive]]s between threads and [[atomic operation]]s, and interface with a CPU-style MMU.
===DSPs===
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The time aware least recently used (TLRU) is a variant of LRU designed for the situation where the stored contents in cache have a valid lifetime. The algorithm is suitable in network cache applications, such as ICN, [[content delivery network]]s (CDNs) and distributed networks in general. TLRU introduces a new term: time to use (TTU). TTU is a time stamp on content which stipulates the usability time for the content based on the locality of the content and information from the content publisher. Owing to this locality-based time stamp, TTU provides more control to the local administrator to regulate in-network storage.
In the TLRU algorithm, when a piece of content arrives, a cache node calculates the local TTU value based on the TTU value assigned by the content publisher. The local TTU value is calculated by using a locally
=====Least frequent recently used=====
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===Web cache===
{{Main|Web cache}}
Web browsers and [[web proxy server]]s, either locally or at the [[Internet service provider]] (ISP), employ web caches to store previous responses from web servers, such as [[web page]]s and [[image file format|image]]s. Web caches reduce the amount of information that needs to be transmitted across the network, as information previously stored in the cache can often be re-used. This reduces bandwidth and processing requirements of the web server, and helps to improve [[responsiveness]] for users of the web.<ref>{{cite web|url=http://docforge.com/wiki/Web_application/Caching|title=Web application caching|author=Multiple (wiki)|work=Docforge|access-date=2013-07-24|archive-date=12 December 2019|archive-url=https://web.archive.org/web/20191212152625/http://www.docforge.com/wiki/Web_application/Caching|url-status=dead}}</ref
Another form of cache is [[P2P caching]], where the files most sought for by [[peer-to-peer]] applications are stored in an ISP cache to accelerate P2P transfers. Similarly, decentralised equivalents exist, which allow communities to perform the same task for P2P traffic, for example, Corelli.<ref>{{cite conference|last1=Tyson|first1=Gareth|last2=Mauthe|first2=Andreas|last3=Kaune|first3=Sebastian|last4=Mu|first4=Mu|last5=Plagemann|first5=Thomas|title=Corelli: A Dynamic Replication Service for Supporting Latency-Dependent Content in Community Networks|url=http://comp.eprints.lancs.ac.uk/2044/1/MMCN09.pdf|conference=MMCN'09|archive-url=https://web.archive.org/web/20150618193018/http://comp.eprints.lancs.ac.uk/2044/1/MMCN09.pdf|archive-date=2015-06-18}}</ref>
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===Content delivery network===
{{
A content delivery network (CDN) is a network of distributed servers that deliver pages and other Web content to a user, based on the geographic locations of the user, the origin of the web page and the content delivery server.▼
▲A [[content delivery network]] (CDN) is a network of distributed servers that deliver pages and other
CDNs began in the late 1990s as a way to speed up the delivery of static content, such as HTML pages, images and videos. By replicating content on multiple servers around the world and delivering it to users based on their ___location, CDNs can significantly improve the speed and availability of a website or application. When a user requests a piece of content, the CDN will check to see if it has a copy of the content in its cache. If it does, the CDN will deliver the content to the user from the cache.<ref name=":0">{{cite web|url=https://people.cs.umass.edu/~ramesh/Site/PUBLICATIONS_files/DMPPSW02.pdf|title=Globally Distributed Content Delivery, by J. Dilley, B. Maggs, J. Parikh, H. Prokop, R. Sitaraman and B. Weihl, IEEE Internet Computing, Volume 6, Issue 5, November 2002.|access-date=2019-10-25|archive-url=https://web.archive.org/web/20170809231307/http://people.cs.umass.edu/~ramesh/Site/PUBLICATIONS_files/DMPPSW02.pdf|archive-date=2017-08-09|url-status=live}}</ref>▼
▲CDNs
===Cloud storage gateway===
{{Main|Cloud storage gateway}}
A [[cloud storage gateway
===Other caches===
The
Write-through operation is common when operating over [[unreliable
[[Web search
[[Database caching]] can substantially improve the throughput of [[database]] applications, for example in the processing of [[Database index|indexes]], [[Data dictionary|data dictionaries]], and frequently used subsets of data.
A [[distributed cache]]<ref>{{cite journal|last1=Paul|first1=S.|last2=Fei|first2=Z.|date=1 February 2001|title=Distributed caching with centralized control|journal=Computer Communications|volume=24|issue=2|pages=256–268|citeseerx=10.1.1.38.1094|doi=10.1016/S0140-3664(00)00322-4}}
=={{anchor|The difference between buffer and cache}}<!--Former section name used in external links-->Buffer vs. cache==
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