All physical systems register and process information. The laws of physics determine the amount of information that a physical system can register (number of bits) and the number of elementary logic operations that a system can perform (number of ops). The Universe is a physical system. The amount of information that the Universe can register and the number of elementary operations that it can have performed over its history are calculated. The Universe can have performed ${10}^{120}\mathrm{ops}$ on ${10}^{90}\mathrm{bits}$ ( ${10}^{120}\mathrm{bits}$ including gravitational degrees of freedom).

• Received 23 January 2002

DOI:https://doi.org/10.1103/PhysRevLett.88.237901