17" Apple iMac - The Official SPCR Review

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Given how important thermal design is to achieving low noise levels, it's quite impressive that there is almost no visual evidence of thermal design: No fan grills, no wide-open (or even restricted) intakes, and no visible heatsinks. The evidence is there if you look for it, but even then the surface area of the intakes and exhaust vents is shockingly small. No doubt the low-power Core Duo around which the iMac is based helps keep heat down a bit, but even then it's surprising how little airflow there seems to be.

Most of the bottom serves as an intake, but the intake grill is quite restrictive...

The main intake is located on the bottom, where more of the thick plastic casing has been cut away to reveal a thin (but restrictive) metal grill. The amount of air flowing through the system must be very small, since no airflow could be felt at the bottom even with the system running full tilt.

There is another small opening in the center of the back panel ... but is it an intake or a speaker?

There is another small vent on the back panel, but no airflow could be felt here either.

The slim white strip at the top is the only point of exhaust.

The exhaust vent is a thin indented strip that runs across the top of the back panel. To a casual observer, it appears to be part of the system's cosmetic design. Only the slight trickle of hot air that we could feel drifting from it betrayed its true function. Even so, the amount of air passing through the system is probably not much more than would be achieved with convection alone.

In addition to the small amount of airflow, some cooling is also provided by direct conduction. As a heatsink material, the plastic exterior has nothing on copper or aluminum, but there is enough surface area that it probably helps a little. In this respect it is like a laptop, which also dissipate heat through plastic. The back of the screen got quite warm to the touch, confirming that some heat was being transferred in this way.

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