Question

What is different between 128 bit and 64 bit ? What is meaning of qubit and different between it and bit ?

Answer 1

In quantum computing, a qubit ( /ˈkjuːbɪt/) or quantum bit is a unit of quantum information—the quantum analogue of the classical bit.
A qubit is a two-state quantum-mechanical system such as the polarization of a single photon: here the two states are vertical polarization and horizontal polarization. In a classical system, a bit would have to be in one state or the other, but quantum mechanics allows the qubit to be in a superposition of both states at the same time, a property which is fundamental to quantum computing.

Answer 2

this will also help http://en.wikipedia.org/wiki/Bit_rate