The iPhone 5S uses a new Apple-designed A7 processor that has a 64-bit architecture. It runs a 64-bit version of iOS 7, which has 64-bit drivers. But why should anyone care about this? Does it really make it better than the 32-bit iPhone 5? Is the iPhone 5S twice as good? See: iPhone 5S vs iPhone 5C comparison review: what's the difference between iPhone 5S and iPhone 5C?
Bigger numbers sound better, but don't fall into this particular trap of thinking that 64-bits is necessarily better than 32-bits, or getting into a "My phone is better than your phone because it's 64-bit," argument. See also: Apple iPhone 5S review.
It's easiest to think of the processor as the heart of a mobile phone, or the engine that powers it. At the launch of the iPhone 5S, Apple made a big deal of the fact it has a 64-bit processor? There is no doubt that one day you will need a 64-bit processor in your smartphone, but you certainly don't need one today. Visit: The best phone you can buy in 2013?