Where is GZIP compression used?
GZIP compression must be installed on the web server, such as in Apache, IIS and nginx. When retrieving the website the web browser will prompt the visitor he/she can receive the GZIP.
Then the web server will send the files GZIP-compressed to the web browser, after which the web browser will unzip them.
If the visitor's web browser does not support GZIP, the files will be sent back to the visitor in their original state (uncompressed).