Informative interview with Facebook employee: Security and soon, Hyper-PHP
More interestingly, Facebook takes snapshots, which includes every viewable screen, essentially a picture of all the data on all of their servers, every hour of every day of every week, 365 days a year. This data is stored on four data centers, including one in Santa Clara, San Francisco, New York and London. Each data center houses approximately five to eight thousand servers, which is about right considering they have 200 million active users (users who have participated on the site within the last month).
Although the employee mentioned that they once had a master password that allowed them to access any account on the site, that is irrelevant considering that all the data, including private messages, emails--everything--is stored within those databases. So anyone with access to those databases has access to the information stored within them.
As far as the programming behind the site, Facebook is working on revamping the site by upgrading it from standard PHP to what they call Hyper-PHP (HPHP), which turns it from a scripted language into a compiled language, which should speed up the site by reducing the CPU usage on their servers by 80%, which will speed the page loading time and make the end-user experience more pleasant. Which means more users, more pageviews, more clicks, and more revenue. This change should occur within the next two months, according to the anonymous employee.
The interview at The Rumus is well worth reading--it's a bit long winded, but informative not only for users of Facebook, but developers and programmers who may gleam a bit of insight into the inner workings of the largest social networking site in the world.