My wife has a 27″ iMac from late 2009. We upgraded her to a more powerful Windows machine about a year ago. The iMac has a beautiful screen and is in good shape, but the performance of it had slowed quite a bit. I took a look at the specs of the machine. It had 4 GBs of RAM and a 1 terabyte hard drive. It also has a Core 2 duo, dual-core processor, which is meh. I figured that there wasn’t a whole lot I could do about the processor, but the hard drive and RAM could be upgraded.
Upgrading RAM on an iMac is supported by Apple and very easy to do on most models. I decided to upgrade it to 8 GBs. I made sure that I bought RAM that was supported by the version of iMac that I was using. I used Crucial’s RAM picker as I have had good experiences with it in the past. On a regular PC I can usually suss out what RAM will be compatible with the motherboard in question. With Macs, I have been burnt by buying RAM that isn’t compatible, so I always check. Actually performing the upgrade was fairly straightforward. I tipped the iMac back so that it was lying horizontal, then unscrewed a panel from the bottom of the monitor housing. As I recall there are some tabs that help you eject the RAM modules. Before you pull the modules out, you may want to take a minute to understand how to put the tabs back before you insert the new modules. It will make it easier to eject the new modules should you ever need to. Also it just looks tidier.
As for the hard drive, we were going from a 1 TB spinning drive, that is probably on its last legs, to a Crucial M500 240 GB SSD. Luckily very little of the 1 TB drive was in use, so I was able to do a full duplication to the SSD before swapping it out. I got a USB enclosure and used SupserDuper! to clone the whole hard drive. There are two annoying things about replacing the hard drive. The first annoying thing is getting access to the hard drive, the second is dealing with the fan and heat sensor issues. I would recommend having two people to help with this part. It isn’t necessary but it may save you quite a bit of time as you won’t have to completely disassemble the iMac. I used a spudger to loosen the screen. I thought that the screen was going to be glued on or maybe held on with friction. The model that I was dealing with actually held the screen in using magnets. Turns out there are very strong magnets all around the rim of the display that hold the glass in place. There are basically these rounded metal spikes on the back side of the glass slot in between the magnets. I hope that this can finally kill the urban legend that magnets are bad for computers. After removing the glass screen we set it aside and cleaned it. That is one of the nice things about the screen being totally separated from the LCD panel, you can easily clean the screen without messing up the panel. The panel sits a couple of millimeters behind the screen. We had to be very careful not to touch or smudge up the panel when working around it. Just to be certain I washed and dried my hands very thoroughly. I had to remove about a dozen tiny screws around the panel. They were very annoying to pull out and put back in as they were located right next to the magnets. After unscrewing the screws we were able to tilt the panel forward. This is where having a helper comes in handy. If you have a helper you can just loosen a single ribbon cable at the top and have your helper hold the panel. If you don’t have someone to help then you may have to unhook more ribbon cables and remove the panel completely from the machine. At this point you can see the drive held in place with a sort of drive tray. In some of the guides I saw, people used double sided tape to affix the SSD to the inside of the shell of the iMac or removing the DVD/CD ROM drive and using an adapter so that you could have 2 drives. I opted to use a 3.5 to 2.5 adapter as I felt it would be cleaner looking. In retrospect I think going with the double sided tape would have been better as the 3.5 to 2.5 adapter I used was larger than the old drive that was in there. When I had everything back together the screen was pushed out a couple extra millimeters. Once the drive was installed, I reversed the whole process to get it back together.
So I alluded to fan and heat sensor issues. That is because the iMac ships with a special hard drive that uses a non-standard interface for sensing the temperature of the hard drive. If Mac OS X doesn’t see this sensor attached then it assumes that the sensor has failed or is at max temperature. This causes it to ramp the fans up to max speed, all the time and this is actually pretty loud. I found a Mac OS X utility called SSDFanControl which monitors the temperature using the industry standard SMART technology. It has a list of supported drives, but as it is using SMART it should in theory work with any drive. This utility was free which is nice as many guides point to a similar utility that actually costs money. After a couple of months of testing, I think it works great.
Overall it probably took an afternoon worth of work, but a lot of that was duplicating the hard drive, which doesn’t require you to be at the computer. Since the hardware upgrade we have upgraded to the new version of OS X, Yosemite, without a hitch. Not everything is faster but surprisingly, tasks that were unusable before now function at what I consider “normal speed”. It was a fun project, and hopefully it impressed the wife!