Someone else might want to know.
If a hard disk drive has fans mounted on it, the fans may not be meant to cool only the drive, but may be meant to help cool the CPU generally. That would explain the destruction of my CPU soon after I replaced a HDD with fans with one or two fanless HDDs, which I did because the fanless had content I wanted.
I replaced a 60GB Western Digital Caviar WD600 HDD model WD600BB-00CAA1 (with the usual outer dimensions ignoring fans) having 2 attached 2" 7-blade fans with 2 HDDs totaling just over 2GB without fans, all IDE or EIDE (I forgot which). The drive holder wasn't big enough for two, so I dangled one using insulated wire as if it was string. I had also added a NIC that worked fine weeks earlier in another machine with the same drives and OS. I disconnected a tape drive that I never used. The case and PSU fans were both breezy recently, although I didn't check if they worked on the day of death. I smelled smoke but saw nothing harmed when I opened the case. Days later, when I plugged it into AC power again, I smelled smoke again. It wasn't ATX or Dell's idea of wire-swapped fire-risking pseudo-ATX but some other form factor. An alternative diagnosis is that it was nearly dead already from an unknown cause.
What I don't know is if it's possible to connect a fan-carrying HDD with a power cable but without the signal cable in order to use only the fan while connecting a fanless HDD with both cables for content, and, even if that's possible, if that's inadvisable because having two HDDs would overheat the space beyond the fan's capacity to cool. It might also be possible to overload some power supplies. I also don't know if unbolting the fan assembly would have exposed the HDD's interior, effectively killing it. If multiple HDDs are mounted, the position of the fans would remain critical to proper system cooling and, even so, the additional HDD might generate too much heat to be cooled enough and maybe the HDD holder's capacity (one HDD) might be a clue. Nor do I know if a fan-carrying HDD can be installed in a CPU not meant for it (in case redirected airflow reduces cooling), although that seems unlikely.