I just upgraded my 2544 base model iMac (2.7 i5, 8gb ram, 5400 rpm HDD) with all possible options: 3.1 i7 3770s CPU, 16gb ram and a Samsung EVO 850 SSD. The upgrades all worked perfectly, and were made possible for an amateur such as myself thanks to these amazingly detailed and well photographed instruction guides. I can't tell you how helpful they were to me, and just wanted to thank you and share my success. I am an amateur with no significant experience at all with computers, so I wanted to encourage anyone who is hesitant to get the right tools for the job and get to it! Thanks again!