What are cookies?

A cookie is a small piece of information which a web-server can send to a users web-browser for the web-browser to store for later use. The web-server can then read the information in the cookie back from the user's web-browser when the user loads a page from that web-server.

Cookies have an expiry date associated with them so that eventually the cookie will be deleted from your computer. How long a cookie takes to expire depends on the lifespan that the web-server set for that cookie when it created it on the user's web-browser.

How are they used?

Cookies are most frequently used as a way to track users and maintain things like on-line shopping carts. The server stores in cookies on the web-browser the items you have in your shopping cart.

Why are they used?

Cookies are usually used as a way to avoid the repeated sending of information between web-browser and web-server or as a way to avoid having to store user-dependant information on the web-server.

Cookie problems

Cookies, like all non-core Internet features, have a number of problems:

• not all browsers support cookies;
• not all users that have a web-browser that supports cookies have the cookies functionality turned on;
• some users have their web-browser configured to alert them whenever a website tries to set a cookie - if your website tries to set many cookies this can be particularly annonying for such users;
• some proxies and caches do not properly handle cookies;
• cookies are set by web-browser and not by user - if the same user logs onto a website using a different web-browser the cookies from the other web-browser will not be available. This is particularly a problem when users access the same website from two different computers such as at work and at home.

Alternatives to cookies

Other than for tracking the number of browsers that view a particular website there are really no good reasons for competent web-developers to use cookies. Instead of using cookies it is possible to store that information in databases on the web-server which avoids all of the problems with cookies listed above.

Cookies are only necessary if a web-developer does not have sufficient control over the web-server to be able to use server-side storage of user information (eg. non-database driven websites) or where the number of users is so huge that server-side storage is not practical (eg. like search engine sites such as <a href="http://www.google.com" class=l>Google</a> which has millions of users and uses cookies to store user search preferences).