A web cache is a mechanism for the temporary storage (caching) of web documents, such as HTML pages and images, to reduce bandwidth usage, server load, and perceived lag. A web cache stores copies of documents passing through it; subsequent requests may be satisfied from the cache if certain conditions are met.^[1]

It should not be confused with a web archive, a site that keeps old versions of web pages.

Systems[link]

Web caches can be used in various systems.

• A search engine may cache a website.
• A forward cache is a cache outside the webserver's network, e.g. on the client software's ISP or company network.^[2]
• A network-aware forward cache is just like a forward cache but only caches heavily accessed items.^[3]
• A reverse cache sits in front of one or more Web servers and web applications, accelerating requests from the Internet.^[4]
• A client, such as a web browser, can store web content for reuse. For example, if the back button is pressed, the local cached version of a page may be displayed instead of a new request being sent to the web server.
• A web proxy sitting between the client and the server can evaluate HTTP headers and choose to store web content.
• A content delivery network can retain copies of web content at various points throughout a network.

Cache control[link]

HTTP defines three basic mechanisms for controlling caches: freshness, validation, and invalidation^[5].

• Freshness allows a response to be used without re-checking it on the origin server, and can be controlled by both the server and the client. For example, the Expires response header gives a date when the document becomes stale, and the Cache-Control: max-age directive tells the cache how many seconds the response is fresh for.
• Validation can be used to check whether a cached response is still good after it becomes stale. For example, if the response has a Last-Modified header, a cache can make a conditional request using the If-Modified-Since header to see if it has changed. The ETag (entity tag) mechanism also allows for both strong and weak validation.
• Invalidation is usually a side effect of another request that passes through the cache. For example, if a URL associated with a cached response subsequently gets a POST, PUT or DELETE request, the cached response will be invalidated.

Browser cache[link]

Web browsers cache content on the client machine, in memory and on disk.

Legal issues[link]

In 1998 the DMCA added rules to the United States Code (17 U.S.C. §: 512) that relinquishes system operators from copyright liability for the purposes of caching.

Comparison of web caches[link]

See also[link]

• Harvest project
• Proxy server
• Web accelerator
• Cache manifest in HTML5

Notes[link]

Further reading[link]

• Ari Luotonen, Web Proxy Servers (Prentice Hall, 1997) ISBN 0-13-680612-0
• Duane Wessels, Web Caching (O'Reilly and Associates, 2001). ISBN 1-56592-536-X
• Michael Rabinovich and Oliver Spatschak, Web Caching and Replication (Addison Wesley, 2001). ISBN 0-201-61570-3

External links[link]

• Caching Tutorial for Web Authors and Webmasters
• Web Caching and Content Delivery Resources
• Web Caching, Web caching in general with some references to SQUID
• Cache control directives demystified Explanations, do's and don't

Look up web in Wiktionary, the free dictionary.

Web may refer to:

Biology[link]

• Spider web, a mesh built by a spider, composed of spider silk and usually used for trapping prey
• Interdigital webbing, skin membranes between the digits of semiaquatic mammals

Computing[link]

• World Wide Web or "the Web", a hypertext system that operates over the Internet
  • Web 2.0, a perceived transition of the Web from a collection of Web sites to a full-fledged computing platform serving Web applications
  • World Wide Web Conference (WWW), a yearly international academic conference on the topic of the future direction of the World Wide Web
  • World Wide Web Consortium, also known as W3C and W3.org, the main international standards organization for the World Wide Web
  • WorldWideWeb, the first web browser and editor
  • Web (web browser), the web browser included with GNOME desktop environment (previously known as Epiphany)
  • Web.com, a public company that offers websites and other services for small businesses and consumers
  • Webs (web hosting), a website which allows users to create free websites
• WEB, a computer programming system created by Donald Knuth to implement literate programming

Publications[link]

• The Web (comics), a comic book character
• Web (novel) by John Wyndham, posthumously published novel set on an island populated by spiders
• World English Bible (WEB), a public domain translation of the Bible
• The Web (series), a series of science fiction stories
• "The Web", a publication by Marillion.

Television, radio and film[link]

• WEBS (AM), a radio station at 1030 kHz, licensed to Calhoun, Georgia, United States
• The Web (film), a film noir
• The Web (TV series), a mystery/suspense anthology series
• "Web" (Law & Order: Special Victims Unit), an episode of Law & Order: Special Victims Unit
• Webs (film), a 2003 sci-fi movie
• The Web, a dangerous region of space in the ReBoot universe
• West End Broadcast (WeB FM), a radio station in Newcastle, England, that was a forerunner of NE1fm
• "The Web", an episode from the first season of the British science-fiction series Blake's 7

Miscellaneous[link]

• In mathematics, a linear system of divisors of dimension 3
• Offset printing web, a roll of paper is used, rather than individual pages
• Steel I-beams or trusses are made with a web, centered between the top and bottom flange
• Web Entertainment, a record label
• "The Web", a song from the album "Script for a Jester's Tear" by Marillion.
• Web (manufacturing) continuous sheets of material passed over rollers
• b:Nets, Webs and the Information Infrastructure

See also[link]

• Webb (disambiguation)
• Webbing: Webbing (textile), Interdigital webbing (Biology).

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

Look up cache, caching, or caché in Wiktionary, the free dictionary.

Cache may refer to:

• Caching or hoarding (animal behavior), a food storing behavior of animals
• Treasure trove, a valuable cache which has been lost, or left unclaimed by the owner, or a place where items are stored
• Geocaching, an outdoor treasure-hunting game

In computing:

• Cache (computing), a collection of data duplicating original values stored elsewhere on a computer
• CPU cache, a small area of fast memory used by the central processing unit
• Disk buffer, the small amount of buffer memory present on a hard drive
• Page cache, the cache of disk pages kept by the operating systems, stored in unused main memory
• Web cache, a mechanism for the temporary storage of web documents to increase performance
• DNS cache, a server in the domain name system which stores queried results for a period of time
• P2P caching, a technique used to reduce bandwidth costs for content on peer-to-peer networks
• Database caching, a mechanism used to cache database content in multi-tier applications
• InterSystems Caché, an object / relational database management system

In geography:

• Cache (Aosta), a frazione in the Province of Aosta in the Aosta Valley region of Italy
• Cache, Illinois, an unincorporated community in Alexander County, Illinois, United States
• Cache, Oklahoma, a city in Comanche County
• Cache Creek (disambiguation), several places
• Cache County, Utah, United States
• Cache, Utah, Cache County, Utah, United States
• Cache Peak (Idaho), a tall mountain in Castle Rocks State Park

Caché may refer to:

• Caché (film), a 2005 film directed by Michael Haneke
• Caché (software), a database management system from InterSystems
• Caché (album), a 1993 album by Kirk Whalum
• Caché, Inc., South Florida women's apparel company rescued by Andrew Saul
• Benedikt de Caché (1740–1809), Austrian diplomat

See also[link]

• Cachet, in philately, a design or inscription other than a cancellation or pre-printed postage
• Cash, money in the form of liquid currency
• All pages with titles containing "Cache"
• All pages beginning with "Cache"
• All pages with titles containing "Caché"
• All pages beginning with "Caché"

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.