If large-scale quantum computers can be built, they will be able to solve some problems much more quickly than any computer that exists today (such as Shor's algorithm). Quantum computers are different from other computers such as DNA computers and traditional computers based on transistors. Some computing architectures such as optical computers may use classical superposition of electromagnetic waves. Without quantum mechanical resources such as entanglement, people think that an exponential advantage over classical computers is not possible. Quantum computers cannot perform functions that are not theoretically computable by classical computers, in other words they do not alter the Church-Turing thesis. They would, however, be able to do many things much more quickly and efficiently.