QWhich of the following is the smallest and fastest computer imitating brain working?

Special Purpose Computer
Special purpose computers are those computers which are used to solve a single and dedicated types of problem. e.g. Automatic aircraft landing, multimedia computer, etc.

Quantum computer was first introduced by Richard Feynman. It uses quantum mechanical phenomena. It is the fastest computer imitating brain working.
Nano computer is a general team used to describe a computer smaller than a microcomputer, usually about the size of a credit card. e.g. Raspberry Pi which could be used in schools to teach science to children.
Pratyush India’s fastest and first multi-petaflops (PF) supercomputer named Pratyush was unveiled at Pune based Indian Institute of Tropical Meteorology (IITM).
Pratyush has 6.8 PF computational power installed at two MoES Institutes. 4.0 Peta Flops HPC facility at IITM, Pune and 2.8 Peta Flops facility at NCMRWF, Noida. Pratyush is fourth fastest supercomputer in the world dedicated for weather and climate research.
Note PF is a measure of a computer’s processing speed.