WARNING: This post was originally published in 2008 and hasn't been updated since.
The tips, techniques and technology explained here may be outdated. If you spot any errors, please let me know in the comments so I can adjust the article. Thanks!
GZip is a formidable way to save up on bandwidth, without hindering your users. It allows any script to pass its content by the compression tool first, before being sent out. The receiver will then receive the compressed file, and unpack it to show its content.
Browsers that don't support GZip will automatically fall back to the normal way of sending out content: unzipped.
It's a win-win situation. You save bandwidth, and don't bother your users. So, let's enable it.
The easiest is way is by using a .htaccess file. Add the following line to it.
php_value output_handler ob_gzhandler
Since not every host allows .htaccess to overwrite certain system settings, you can also define this in your PHP pages itself, as described on the following page: Other Methods to Enable GZip Compression.
You can quickly test the result of your compression, at the following website: compression / deflate / gzip test tool.
There 's a (relatively) small downside to this: it requires a bit of CPU power from your webserver to compress the page, and a bit of CPU power from your visitor to decompress the page. This probably won't be an issue, unless you have a very busy server.