mod_Deflate Test
Apache web servers can be configured to use HTTP compression. When HTTP compression is enabled, Apache which serves web pages to visitors, will compress the files it is sending out (for example HTML files). Apache does not cache or store compressed files; it will compress every file over and over again each time it is requested.
The advantage of HTTP compression is that the transmitted files are smaller. This means that your site will be loading much faster, and it also means your server will be using less bandwidth. The disadvantage of compression is that it requires more processor (CPU) power. However, because the files Apache is serving are smaller, it will use less resources so this cancels out the higher resource usage almost completely. You should not be worried about browsers needing extra time to load a page because they need to decompress the files, shorter loading times more than cancel out the extra decompression time, and besides, we all own extremely capable computers for compressing such small files.
The old first version of Apache needs an extra module to be installed before webmasters can activate HTTP compression. The compression module for Apache 1.3.x is called mod_Gzip. Mod_Gzip has various compression levels, however, using a compression level above 2-3 serves no point. Increasing compression above that level only allows for very small size decreases, while requiring substantially more processing power. Your site would actually start to run slower.
The new Apache 2.2.x HTTP compression module is called mod_Deflate. Good news for every webmaster running the newest Apache version: mod_deflate is already installed on your server, all you have to do is enable it. Simply pull up the Apache documentation and it will explain how to enable HTTP compression for your server.
You can use this page to test if mod_Deflate or test if mod_gzip are enabled for your site, or for any other site. An example of a site using HTTP compression is this site, but also Google uses HTTP compression. Below you can also see if your browser supports HTTP compression.