Nanocomputer
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.)
The term nanocomputer is increasingly used to refer to general computing devices of size comparable to a credit card. The first use of this name appears to be to describe the s1mp3 manufactured by The Flying Electron Inc. (7 November 2008). It is now used for a wider range of devices, such as