The largest fastest and most powerful are called supercomputers. Supercomputers are mainly used for weather forecasting remote sensing image processing, biomedical applications etc. Examples of few supercomputers are Cray Y- MP/ 832 Cray 2, NEC SX -3 etc. In India we have Cray XMP 14 supercomputer used by Meteorological department.
Important: Actually it is difficult to categorise computers according to this classification due to very fast growth of technology. For example latest microcomputer may be better than old mini or mainframes.