The HTTP protocol used by web browsers and web servers contains provisions for proxy servers. In addition, most major Internet Service Providers (ISPs) now run "transparent" proxy servers without your browser being directly aware of it. This is done by intercepting Internet packets that are recognized to be part of the HTTP protocol and silently redirecting them to the proxy server rather than sending them directly to the intended web server. When an ISP such as America Online has many customers, this can result in a significant speed increase, because pages can be cached "closer" to the users. It also provides an opportunity to work around slow modem speeds; the proxy server can convert large image files to a more compact format, at a considerable cost in quality, and send those lower-quality images on much more quickly to web browsers that request the original images.
Got a LiveJournal account? Keep up with the latest articles in this FAQ by adding our syndicated feed to your friends list!