Hi all, I have a Late 2009 27" iMac which I have discovered has a SATA HD Seagate dated 11/2012 which was running silently. Either the GPU or Screen died (according to Apple Care phone support) giving yellow vertical lines. I replaced it with a Mid 2010 11.3 27" Imac and the Samsung SATA HD in it is grumbling away and has become a distraction. From what I've read its fairly normal for them. I wish to take the newer HD from the older machine and install it into the newer machine. 1) will this HD work in this situation? will it need formatting? (I suspect not! as it came for another iMac) 2) Once physically install is done and I correct to complete installation by holding Command R during start up and installing my external Back Up HD via USB to re-insall OS and all contained within ? Any advice appreciate to help this novice achieve and improvement to this out of date beast!!!!