A web server refers to either the hardware (computer) or software (application) that helps deliver web content.
- apachectl a command line tool for controlling Apache.
- a2enmod/a2dismod a command line tool for enabling and disabling Apache2 modules.
A web server is responsible for and should be configured to set HTTP cache headers (see HTTP > Caching) appropriately.
A web accelerator serves as a front for your web server, speeding up delivery by various techniques including full-page caching and gzipping responses. Varnish is a popular, open source example.