A web cache is a file folder in a web browser that stores data from the web pages a user visits. It provides a way for one to more quickly view web content from sites the user has previously visited, and it stores images, web scripts, multimedia files and other website content. Both web browsers and proxy servers implement a cache that can reduce the time needed to get information, reduce a network's load, reduce data transfer costs and improve the network's accessibility.
The most common type of web cache is the browser cache, which stores images, streaming video data, JavaScript® files, cascading style sheet (CSS) files and other content that appears on websites. When a user visits a website, the browser first looks for the content in the browser cache. If the user has previously visited the website, the cache usually contains a stored copy of the site's content, so the browser doesn't need to download the page again from the web server. Cached material has an expiration date to ensure the user will not be viewing outdated content. When the accessed web page's content changes, the site's data in the web cache also will be updated to reflect these changes.
Another type of web cache exists on networks that implement a proxy server. When a user navigates to a website in his or her browser, a request is made to the proxy server to check on whether that specific website already appears in the cache. The proxy server cache contains data from websites visited by all the network's users. If the material already exists in the cache and is not stale, then it won't need to be downloaded again from the Internet. Caching data on the local area network can help improve accessibility and efficiency on networks with high traffic or limited bandwidth.
Both types of web caches have their own advantages and disadvantages. The browser cache and proxy server cache both allow users to access website data more quickly. A proxy server cache is especially useful for large networks that have numerous users, provide limited bandwidth, experience high data usage and implement streaming video or Voice over Internet Protocol (VoIP). Either kind of web cache can have disadvantages if material is not updated quickly enough and if the browser or proxy server is not configured to cache certain types of data. The cache also may quickly fill up if only a small amount of space is available.