1. Robots.txt - standard for robot exclusion. http://www.robotstxt.org, 1994.
2. Apache ttfb module. http://code.google.com/p/mod-log-firstbyte, 2008.
3. Memcached - open source distributed memory object caching system. http://memcached.org, 2009.
4. Google official blog: Using site speed in web search ranking. http://googlewebmastercentral.blogspot.com/2010/04/using-site-speed-in-web-search-ranking.html, 2010.
5. Apache httpd server. http://httpd.apache.org, 2011.