A computer made from components (mechanical, electronic, or otherwise) on a nanometer scale.

a classical computer that may rely on quantum states to carry out classical computations

a computer whose physical dimensions are microscopic

A computer with parts built on a molecular scale.

Nanocomputer is the logical name for a computer smaller than the microcomputer, which is smaller than the minicomputer. (The minicomputer is called "mini" because it was a lot smaller than the original (mainframe) computers.) More technically, it is a computer whose fundamental parts are no bigger than a few nanometers.