The D-Wave computer is unusual because it uses quantum bits (qubits) — bits that can exist in two states, on and off, simultaneously — to speed up calculations, and because it does not operate on the normal 'gate' model of computing, whereby logic gates are used to manipulate those bits. Instead, it is an 'adiabatic' computer, which reads out the ground state of its qubits to find a solution. The academic community has favoured the gate model, which has a better-developed theory behind it. But the adiabatic model has proven much easier to build, allowing D-Wave to double its processor size every year. The D-Wave Two has 512 qubits.