Titan uses an innovative approach of large scale use of GPUs (Graphics Processing Units) to supplement the processing power of CPUs (Central Processing Units). It uses 18,688 Nvidia Tesla K20X GPUs in conjunction with more than 560,640 AMD processors. GPUs are more efficient for certain types of applications and were originally developed to improve 3D graphics for high-end computer games, underscoring the point that gaming is serious business.
Like most top-ranked supercomputers, Titan uses a Linux operating system. It runs the Cray Linux Environment, which is based on SUSE 11.
BTW, one petaflop is one quadrillion (15 zeros) calculations (floating point operations) per second. For more information about Titan see the report on the Oak Ridge National Lab web site.