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I am not saying this claim is bogus, but I do not believe it at face value, either.

Reading the Wikipedia page on SATA (http://en.wikipedia.org/wiki/Serial_ATA#Cables.2C_connectors...), I loose track as to the number of different SATA power connectors in existence.

So, it could well be that that new connector is SATA standard, but rarely seen in the wild.

Similarly, on-board temperature sensors could be in some SATA standard/extension/optional API. http://www.cyberciti.biz/tips/howto-monitor-hard-drive-tempe... to point in that direction. It states "hddtemp utility will give you the temperature of your hard drive by reading data from S.M.A.R.T. on drives that support this feature. Only modern hard drives have a temperature sensor."

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If you read the article a little more carefully, you'll understand that it's still the same SATA 15-pin connector (I mean if it wasn't, you would have seen articles about how you couldn't swap hard drives at all).

But what OWC is claiming is that now, instead of using pins 4,5,6 and 12 for ground - that the new iMacs and harddrives inside them are using some of those pins for communication, specifically temperature sensor.

This is outside of the SMART specification, which passes information about the harddrive over the data cable (not the power cable).

So you can swap in any harddrive you like - but if your harddrive doesn't have the functionality / firmware in it to communicate temperature information over the power cable, then the fans kick in.

At this point, I'm offhandedly wondering if this is related more to the Intel Z68 chipset / Smart Response technology somehow.

In addition, OWC is claiming that there's "Mac specific" firmware because they swapped out an identical model harddrive and ran into an issue - but (playing devil's advocate), if these are new temperature sensors involved, a firmware upgrade wouldn't cut it - the harddrive would still be missing said sensors.

I would believe OWC more if they swapped the boards on the harddrives while leaving the platter casing intact.

I reread it, and that indeed seems what they are claiming. I still think this extraordinary claim needs more evidence to be accepted as true. I think SATA has two connectors because one runs to the power supply, and the other to the main board. If that power connectors carries data, how does that data get to the main board? Is the cable split? If so, why would they do that if there already is a data connection to the cable? Or is this a way for a CPU in the PSU to power off of the drive if things go really wrong?

SMART hard drives have existed for more than 10 years, close to 15 years, and they have all had temperature measurement.

The temperatures measurement is very easy to get using SMART, there is absolutely no reason Apple needs to get the data in some proprietary method on extra wires.

hddtemp uses SMART to get the data, and it uses the regular SATA data cable to do it.

I'm guessing that the fans are controlled by the PMU. The PMU runs independent of the main CPU, and I'm guessing that this approach is easier than having the PMU talk to the drives through the SATA controller, requiring drivers, OS support so that the OS SATA driver and PMU doesn't interfere with each other etc.

Correct. However in this case it's the SMC managing it. PMU comes from the PPC era, like CUDA in the clone and 68K times.

SMC handles all low level monitoring, because it's OS independent reading data via SMART is just a non option. SMC also takes care of how hardware components are initialised and a slew of other things. See > http://support.apple.com/kb/ht3964

Secondly, while you can override certain SMC values like fan speeds you can never override the lowest safe values that are hard coded in. In that same vein if the SMC thinks your fan should run faster when you don't want them to, they will regardless.

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