Link prefetching

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Link prefetching is a standards compliant mechanism used by some web browsers, which utilizes browser idle time to download or prefetch documents that the user might visit in the near future. A web page provides a set of prefetching hints to the browser, and after the browser is finished loading the page, and after an idle time has passed, it begins silently prefetching specified documents, storing them in its cache. When the user visits one of the prefetched documents, it can be served up quickly out of the browser's cache.

As prefetching is a standard, examples of prefetching can be divided into standard compliant and non-compliant:

1 Compliant prefetching
2 Non-compliant prefetching
3 Browsers supporting prefetching
4 Sites using prefetching
5 Criticisms
6 Notes
7 See also
8 External links

[edit] Compliant prefetching

Prefetching is not currently explicitly defined by any accepted standards, but Mozilla have announced work on an Internet Draft, that will match the implementation in Firefox^[1].

<link rel="prefetch" href="http://www.example.com/">

[edit] Non-compliant prefetching

Forcing links to be prefetched when they are not specified as prefetchable^{[citation needed]}.

Fasterfox has an option to enable this.

[edit] Browsers supporting prefetching

iCab was the first browser (February 2001 or earlier[1]) to support prefetching
Mozilla Application Suite (Firefox etc.) and its derivatives - the first browser to support prefetching^{[citation needed]}.
browsing using a Google Web Accelerator (maybe technically called precaching)

[edit] Sites using prefetching

Google is the first well-known website that takes advantage of this feature so as to improve the user experience. If the first hit is considered very probable to be the desired hit, it is assigned as a prefetchable link.
Web Album Generator is a free program that creates photo albums which utilize link prefetching.

[edit] Criticisms

Users who pay for the amount of bandwidth they use find themselves paying for traffic for pages they might not even visit.
Webmasters who pay for the amount of outgoing traffic on their sites, are forced to pay for traffic generated by people who may never actually visit their sites.
Advertisers pay for viewed ads on sites that are never visited.^{[citation needed]}
Browser usage statistics are skewed heavily towards browsers that implement prefetching.^{[citation needed]}
Search engine referer statistics are skewed heavily towards search engines that implement prefetching.^{[citation needed]}
Web site statistics become unreliable due to registering page hits that were never seen by the user.^{[citation needed]}
Users may be exposed to security risks as drive-by downloads become more advanced and diverse.^{[citation needed]}
Users may find themselves at considerable legal risk if illegal content is prefetched.^{[citation needed]}