Apple multi-sources its components, and so three such temperature cables exist, for use with WD, Seagate and Hitachi drives. Each manufacturer uses a different style of diagnostic connector, so a vendor-specific cable is installed in these iMacs to match with the drive to be installed - if a Western Digital drive was going to be installed, a cable with a WD connector would also be installed, for example. The iMac read this value through a cable connected to the drive’s diagnostic serial connector, located next to the SATA connector.

The next generation of iMac, the Late 2009 model, leveraged the temperature sensor that all manufacturers build into their drives (as part of the SMART diagnostic suite) instead of relying on an external sensor. I did this on my own 20″ 2007 iMac with no ill effects. Want to replace your hard drive? No problem, just peel the thermistor off of the old one and install it on the new one, and your iMac will be none the wiser. The original aluminum iMacs read the temperature of the hard drive through a simple stick-on thermistor. (Fan control isn’t the responsibility of the operating system it’s a low-level function of the motherboard itself, but the OS does have the ability to interface with it - this is how applications such as smcFanControl are able to work.) Built into the motherboard is a baseband management controller (BMC), which is responsible for monitoring all of these thermal sensor readings and cause the one or more internal fans to spin faster or slower as appropriate. Multiple temperature (thermal) sensors inside the machine measure the heat output by such things as the CPU, video card, optical drive and hard drive.

How iMacs Measure Hard Drive Temperaturesįirst, an explanation of Apple’s overall temperature management system in iMacs. I recently picked up the Samsung SSD seen above and decided that there was no better time to tackle this issue, since it would be one I’d have to deal with on my own iMac. Mass confusion and anger spread across the Internet once an inkling of what was going on was discovered, but so far I’ve seen no single, definitive explanation of exactly how the system works. The level of complexity with which this system operates has increased with every model, and reached its ultimate with the Mid-2011 iMacs. Starting with the original aluminum iMacs, Apple began monitoring the temperature of the internal hard drive so that the system’s internal fan could be optimized.

There’s been at least a few models that have even shipped without internal fans just to make the machine as quiet as possible (often to the detriment of reliability). Apple has always pushed the envelope when it comes to hardware design, especially when it comes to the level of noise that its computers produce.

Internal hard drive for imac