What generation of computer require air conditioner?

Answer 1

All really large computers regardless of generation need an active cooling system (e.g. air conditioner, circulating liquid Freon, circulating chilled water) to dispose of their waste heat.

I even have a quad-core microprocessor desktop computer that uses an internal sealed liquid coolant system to transport the waste heat from the microprocessor to the blower. The air leaving this computer's vents can be hot enough when it is working hard that it would really help if the room had an air conditioner!

1. first generation (vacuum tube) computers all needed internal active cooling systems, because vacuum tubes produce very large amounts of waste heat even when idle!
2. second generation (transistor) computers may or may not have needed internal active cooling systems, but the computer room they were installed in was usually air conditioned to the point of being uncomfortable to be in (except for the smallest machines in this generation, some of which could be installed in ordinary office rooms).
3. third generation (integrated circuit) computers only large machines (e.g. supercomputers) needed significant internal active cooling systems (which were usually either circulating liquid Freon or circulating chilled water), although usually no longer necessary for most computers of this generation the computer room they were installed in was usually air conditioned to the point of being uncomfortable to be in.
4. fourth generation (microprocessor) computers have usually not needed internal active cooling systems, with the exception of very high performance multicore microprocessor systems and microprocessor based supercomputers.