A computer is any computation device, ranging from crude mechanical devices for solving simple mathematical tasks, to massive planet-spanning sentient neural networks, to cybernetic cranial implants and the artificial brains of robots. Some might even argue for the inclusion of natural thinking constructs such as the brains of biological organisms into this category, but generally these are left out.
History of computing
An optical computer processes information using light instead of electrons.
Each stream of photons represents an independent sequence of data, thereby providing extremely massive parallel computation. Nanooptical computers can use a single photon as a bit.
The basis for data in a quantum computer is a qubit, which unlike the bit in a binary machine which encodes either a one or a zero, encodes both possible states at the same time, a quantum superposition of 0 and 1. Thereby not only reducing the time needed for processing complex mathematical equations, such as the factoring of very large numbers, by at least three orders of magnitude; this is done by directly manipulating the probability amplitudes at the gate level.
The latest advance in computer technology, tachyon computers were the inevitable result of FTL communications. Based on using particles that move faster than light (collectively referred to as tachyons) for data processing, they are capable of amazing computational power. At this level several peculiar relativistic effects are observed, such as the paradoxical possibility that a computer may arrive in a solution to a problem before the problem is even inserted by users. Tachyon computers thus require extremely sophisticated programming, relativistic memory buffers and paradox compensator subroutines to prevent the system from corrupting itself with unexpected input from the future.
Singularity computing is the experimental field of using singularities, or miniature black holes, as computers. With a mass density close to infinity, singularity computers promise instantaneous solutions to computing problems. The energy and material requirements for such operations are tremendous, however.