Quora uses the Pylons and Comet technologies for its backend and Ubuntu Linux as its operating system with MySQL as its database. It also uses Git and memcached. Quora uses Nginx as a reverse proxy server and HAProxy for load balancing. Quora has developed its own algorithm for ranking answers, which works similar to PageRank.Quora uses Amazon Elastic Compute Cloud technology to host the servers that run its website. In August 2011, Quora switched its infrastructure's Python implementation from CPython to PyPy, in order to improve response time.
Well for servers and power supply we need to peek into their headquarters which is not possible for me.
The best thing to do is use Quora for your own benefit and keep your curiosity high about their operations and wait for some Quora employed person to explain it to us (if that is not some form of espionage).