[Gooserider]

Per the very long, and somewhat dated but still informative article on all about the innards of hard drives, on that site; by FAR the biggest single source of heat on a drive is the motor and platter assembly!

The heat comes from spinning the platters up against the friction of the air in the drive housing, and the heat is dissipated to all the metal surfaces in contact with that air. This includes the sides, the lid, the body under the PCB, etc. Since the heat is spread over such a large area, none of the areas feel like they are getting all that hot, but the total is still pretty high.

Note also that most of the heat is spread by convection, not conduction. This should be fairly intuitive given that big air-mixer inside the drive housing.

Supposedly, putting a cold spot anywhere on the drive will cool the entire drive effectively. The heat that is being generated and transferred to the case by convection will mostly transfer to the cooled area (by heat flow laws) and the hotter parts of the case will eventually xfer their heat to the cooler area by conduction. I suspect that if the heat coming off the drive body is removed, the chips on the PC board will come back down to reasonable temps.

Another interesting data point - because drives can be face mounted on the PCB side, it is a design requirement that the drive body ledge around the outside of the drive be HIGHER than the tallest component on the PCB. (some drives also leave the motor housing at the same level as the ledge, it's easier to mill it that way, and MIGHT provide extra cooling) My former employer used drive arrays with hot-swappable housings holding the drives. The drives were face mounted, with NO air circulation on the PCB side, but forced air flow over the lid (mostly) and sides (a bit). This is a fairly standard design for SCA based hot pluggable arrays, one of the prime users of the high RPM drives, and they don't overheat in that application...

Gooserider