So I've just received my new iMac, a 27 inch base model with a 3TB Fusion Drive. I had one unanswered question which was "Would the HDD part of the Fusion Drive be spun down most of the time, and therefore be silent most of the time" It seems reasonable to expect it might be, but the answer is a resounding "NO, the HDD part of the Fusion Drive is constantly spinning and never spins down" So to anybody wondering if it's noisy, like I was, the answer is "YES it is noisy" it's a 3.5 inch hard drive constantly spinning 2 feet from your ears noisy. Here's a test: Select "Shut down" and then close your eyes. Can you tell when the computer switched off? A) Nope. B) I think so but it's really hard to tell. C) Yes I can hear a difference, but i didn't notice the noise when it was on. D) Yes, thank god, I feel a tangible sense of relief now that constant 'shhhhhhhhhhhh' noise has gone. I live in the suburbs and have double glazing, so work in a quiet home office. For my iPad the answer is A. (obviously no fans no HDD) For my Macbook Air the answer is B. (very quiet fan only, effectively silent) For my new iMac the answer is D. I messed around with the settings and set the HDD to spin down after 1 minute, It was night and day. I could just make out the noise of the fan afterwards but it's much much quieter. Unfortunately the disk immediately spins back up as soon as the Fusion Drive is accessed, which is as soon as you do anything. This is a fresh install with only 14GB allocated so it's no where near needing the HDD. I think an SSD only iMac would answer C in my test and be considered "quiet". The Fusion Drive version however is not a "quiet pc" **. I'm going to contact Apple and confirm that this is the intended behaviour, if I can. But personally I'm not sure if I want to listen to this hard drive for the next 5 years, so I regret it might have to go back. A real shame as it is such a great machine in all other respects. ** Obviously these opinions are always subjective, and depend on your environment etc, and there will obviously be many more noisy computers available in the world, but in 2013, in comparison to a MacBook Air and other SSD based Apple systems I don't think the iMac with an HDD can be classified as a quiet PC anymore.