The Rev A-D (233mhz-333mhz) had the internal fans. The ones with 350mhz or higher don't have fans. Having a 333mhz and 500mhz indigo the only problem I found was burning discs. I usually got a media error, I would have a fan blowing on the case and shut down the mac, after that the same project would burn no problem. I also agree with the person said that said that the CRT throws off a lot of heat.