Since Late 2009, there’s been a well-documented issue with the iMac line. If you upgrade the hard drive, the fans can start spinning like crazy. The fans at high speed are loud, mainly unnecessary, and have caused a lot of headaches for DIYers everywhere.

The reason the fans spin this way has to do with the iMac’s method of hard drive temperature sensing. Prior to 2009, sensors were placed outside the hard drive to gauge how warm the drives were – if they got too hot, the fans turned on to keep everything nice and cool. This method was simple, effective and made changing, exchanging, or upgrading the main hard drive a relatively simple task.

With the release of the Late 2009 iMac, Apple changed the way the iMac communicates with the drive for that heat-sensing information. Each brand of hard drive Apple used had its own specific thermal sensor cable which connected to certain drives that featured internal temperature sensing. We found that you could still change the drive, albeit with a limited selection. Seagate drives could be swapped with larger capacity Seagate drives; Western Digital could be swapped with other Western Digital Drives; and so forth. There were also reports of other workarounds which included replacing the internal sensor with an external sensor (like the one from the optical drive bay), controlling the fans with software, or purchasing a replacement cable that matched your brand of new hard drive. In any event, there were perhaps a few convoluted ways to upgrade your iMac’s main drive outside of Apple’s offerings for greater speed, more capacity or to quickly restore a machine from a drive failure yourself.

This time around, Apple has changed the game again.

For the main 3.5″ SATA hard drive bay in the new 2011 machines, Apple has altered the SATA power connector itself from a standard 4-wire power configuration to a 7-wire configuration. Hard drive temperature control is regulated by a combination of this cable and Apple proprietary firmware on the hard drive itself. From our testing, we’ve found that removing this drive from the system, or even from that bay itself, causes the machine’s hard drive fans to spin at maximum speed and replacing the drive with any non-Apple original drive will result in the iMac failing the Apple Hardware Test (AHT).

In examining the 2011 27″ iMac’s viability for our Turnkey Upgrade Service, every workaround we’ve tried thus far to allow us to upgrade the main bay factory hard drive still resulted in spinning fans and an Apple Hardware Test failure. We swapped the main drive out (in this case a Western Digital Black WD1001FALS) with the exact same model drive from our inventory which resulted in a failure. We’ve installed our Mercury Pro 6G SSD in that bay, it too results in ludicrous speed engaged fans and an AHT failure. In short, the Apple-branded main hard drive cannot be moved, removed or replaced.

To add insult to injury, the latest iMac EFI Update 1.6 unleashed 6Gb/s speeds on two internal ports – and naturally, one of them is the proprietary, firmware-limited, 7200RPM main drive that can’t take advantage of those speeds anyway.

Now this isn’t to say that our Turnkey Upgrade Program isn’t going to include the new model iMacs. The external eSATA port, or adding hard drives or SSDs in addition to the main hard drive are still perfectly viable and working options in our testing so far. But it isn’t looking good at the moment to have the option to upgrade or even replace the main 3.5″ hard drive as shipped from Apple.

It really begins to raise questions: Is this planned obsolescence at work, or is the freedom promised in 1984 being revoked?

Hard drives fail. It is not a matter of “if” but rather a matter of “when” your hard drive is going to fail. We preach this all the time in regards to having a proper backup strategy in place to prepare from when that failure happens. But it seems now, that when that happens to the main drive on your iMac, you’re left with two options – buy a new drive from Apple and have them install it via one of their Authorized Service Centers, or enjoy the rather large Apple logoed paperweight on your desk. Want a 3.5″ drive larger than 2TB? Too bad – Apple doesn’t offer them.

As die-hard Apple users, we tout all the time that its OK that Apple machines cost more initially, since they’re built better and last so much longer than their PC counterparts. Besides, there’s places like Other World Computing that help keep those aging Macs still powering along as viable machines with upgrades and accessories designed to give you the most out of your Mac investment.

I actually purchased a 27″ 2010 iMac Core i5 earlier this year. I was a bit nervous about Apple’s apparent push toward making OS X more iOS like and wanted the option to upgrade or opt to stay with Snow Leopard for my home machine. I was feeling the buyer’s remorse, just a little bit, when Apple added, not one, but two Thunderbolt ports to the back of the latest model. That kind of speed down the line would certainly allow for plenty of future storage expansion. Once Thunderbolt equipped enclosures finally come to market and all the bugs are worked out, of course. I’m just not the “early adopter” type.

I gotta be honest, I’m not feeling one bit of that remorse anymore. I have a machine that I’m certain I can keep maintained myself with products from OWC for many years to come. If my main hard drive does fail, I know I have options available to replace it. If I need an overall speed boost, I know I can get an OWC Mercury Extreme SSD and install that as my boot drive. If I find I need a faster connection than FireWire 800, I can always add a high-performance eSATA port through the TurnKey Upgrade Program. In short, I have multiple options available to me to configure my iMac to my particular needs.

New iMac envy? Nah…I’ll take the freedom of choice over limitations any day of the week.

UPDATE 8-23-11:

We’ve developed a workable hardware solution to the fan sensor problems and are now offering it as part of our Turnkey Program for 2011 iMac.