I have an early 2010 (Jan) iMac 27" Dual Core with a built in 1TB Hitachi Disk. I have now reached the point where I want to upgrade the internal disk to at least 2TB (preferably 3TB) and add a steady state drive for speed (2nd priority). I have external Harddisks but this is not a substitute for a bigger primary disk. There is a lot of talk out there about sticking to the same make as the original for the RS232 connection that gives the disk temperature to the motherboard for fan speed consideration. Here are my questions: - What disk(s) will work exactly for my model iMac? - Do I have to replace it with a Hitachi disk? - Can an additional SST drive be installed without a problem? - once the new HDD is in, where does the OS come from? - I have a full back up on 2 separate discs through time machine but can make a complete back up once more if necessary to one disk In short, I want to know if anyone has done this and if it is easy enough to do DIY.