University of Michigan has created what seems to be World's Smallest Computer. Named Michigan Micro Mote (M3) which has 0.3 mm x 0.3 mm dimension can be dwarfed by a grain of rice has seen below:
The computer has RAM, photovoltaics, processors and wireless transmitters and receivers. They are too small to have conventional radio antennae so they receive and transmit data with visible light. A base station provides light for power and programming, and it receives the data.
This computer is designed as a precision temperature device with an error of 0.1 degrees celcius. The purpose of this computer is to detect temperature differences between normal cells and tumour cells so that they can be detected, classified and treated.