Mod_deflate is an Apache Web server module installed on all of our Linux hosting accounts by default; it does not have to be installed and supports all mod_deflate functionality.
Mod_deflate compresses content returned from your hosting account using the zlib compression algorithm. You should only use mod_deflate on text, such as HTML, CSS, JavaScript, and XML. Multimedia files are usually already compressed; using mod_deflate on these types of files does nothing and can result in slower page-load times.
For more information, see Enabling mod_deflate with Your Hosting Account.