A cache is a store. Browser software uses a cache to store web page code, text and image files. When you view a page for the first time on the World Wide Web, these files must be downloaded to your computer screen before you can view them. This is why some pages appear to take a long time to build up on your screen.  If you return to that page again, your browser can load these files straight from the local hard drive of your computer. The result is that you see the page load much faster.

The downside of caching is that the web page may have been changed since you last viewed it. In this case, the files stored on your hard disk will be out of date. Fortunately, most browsers have a setting you can use that forces it to contact the web server to see if any files have changed since you loaded the files into the cache. If the files have changed, the browser will download the updates into your cache.

Proxy Server Caching

There are more ways to decrease the time taken for a web page to appear in your browser other than client side caching of pages. If you are working on a local area network with Internet access, it is likely that you are working through a proxy server. These servers act as a barrier between your computer and the Internet. However, they can store or 'cache' web pages that are frequently requested by users of the network. This means that even if you clear the local cache on your computer you will still receive the page from a stored cache - except this time it is from the proxy server. When client computers are configured to use a proxy server, all their Internet requests pass through the proxy server. If the proxy has a copy of the page in its cache, this is delivered back from the cache to the client. You can force the proxy server to reload the page from the Internet in Internet Explorer by pressing the F5 key with the CTRL key held down (called a 'hard refresh').

Benefits of Proxy Servers

There are several  benefits to using a proxy server as an intermediary between the user and the Internet. These are:

• Reduces the amount of bandwidth used. When a web object has been downloaded, all further requests for this object are met by the proxy server, reducing network traffic.

• It saves hard disc space on the client computers. Caching locally can take up a large amount of space on a client computer reducing performance.

• The speed of web page access is greatly increased compared to fetching it  from the Internet. Having a local cache of frequently visited pages is very useful if Internet access is lost for any reason or if the Internet is experiencing heavy congestion.