Link prefetching

Link prefetching is a draft 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 an Internet Draft standard, examples of prefetching can be divided into standard compliant and non-compliant:

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 [cite web|url=http://developer.mozilla.org/en/docs/Link_prefetching_FAQ#Is_link_prefetching_standards_compliant.3F|title=Link Prefetching FAQ|accessdate=2007-03-23] .

Non-compliant prefetching

In opposition to the Internet Draft, by forcing links to be prefetched when they are not specified as prefetch links.
* Fasterfox has an option to enable the prefetching of all page links by the browser.

Browser support

*iCab was the first browser (February 2001 or earlier [http://lists.webjunction.org/wjlists/web4lib/2001-February/005076.html] ) to support prefetching
*Mozilla Application Suite (Firefox etc.) and its derivatives - the first browser to support prefetchingFact|date=February 2007.
*browsing using a Google Web Accelerator (maybe technically called precaching)

ites using prefetching

Notable sites include:
*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.
* [http://www.ornj.net/webalbum/ Web Album Generator] is a free program that creates photo albums which utilize link prefetching.

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 (non-compliant prefetching)
* Browser usage statistics may get skewed towards browsers that implement prefetching.
* Search engine referer statistics may get skewed towards search engines that implement prefetching.
* Web site statistics may become less reliable due to registering page hits that were never seen by the user.
* Users may be exposed to more security risks - by downloading more pages, or from un-requested sites (additionally compounded as drive-by downloads become more advanced and diverse).
* Web providers may find themselves at liability of third-party content outside of their domain that could be hot-swapped, however search engines has made it heavily accepted than one should have no liability of what one links to, and this is only slightly different through making it more mandatory that one gets the links content.

Notes

See also

* Prefetching

External links

* [http://www.mozilla.org/projects/netlib/Link_Prefetching_FAQ.html Mozilla Link Prefetching FAQ]
* [http://www.google.com/help/features.html#prefetch Google Help: Search Features]
* [http://gemal.dk/browserspy/prefetch.php Test for Prefetch support]