The fourth generation fixed the heating problem with water cooling and air conditioning to prevent the motherboard and CPU's from melting under the heat of the powerful machines. These are the computers that santa probably bought you if you were good this year. The CPU's also advanced for more performance such as a higher RAM and a more crisp and clean picture. This computer used a LSI (Large Scale Integration) to squeeze even more components into a micro chip and eventually went to the VLSI (Very Large Scale Integration) to fit hundreds of thousands of components into one small chip. ULSI increased that number to millions.