The iMac is a very capable system that combines a quality display with a powerful set of hardware. The iMac is used by a wide range of users for everything from everyday home applications to video editing. One of the most common upgrades made to the iMac is a RAM upgrade. This can be performed by the user without sacrificing warranty or the need of any tools other than a Phillips-head (also known as crosshead) screwdriver.
The first thing you’re going to want to do is make sure that you’re getting the right aftermarket RAM for your iMac. Apple provides a detailed outline of the RAM you need, depending on your model of iMac here. All you need to know is the year and size of your iMac.
On Lion, this can be done by going to About This Mac and clicking More Info. You can also determine the model using the model number and this guide: How to Identify iMac Models.
Once you’ve determined what kind of RAM needs to be purchased, it’s a good idea to buy RAM in matching pairs. Upgrading by adding a single stick is okay, but there are some benefits to be had by pairing RAM. If you’re upgrading RAM on an i3, i5, or i7-based iMac, it’s important to note that it will not start with a single DIMM installed on a bottom slot. You can get it to start with a single DIMM placed in a top (closest to the display) slot, however. iMac models running on Core 2 Duo processors can operate using a single DIMM in any of the four slots.
To access these slots, you’ll need to unplug your iMac and lay it face-down on a flat surface, preferably covered by a soft cloth that won’t scratch the glass. At this point, you’ll want to raise the stand so you have clear access to the memory panel along the bottom of the iMac.
By unscrewing the three screws, you’ll expose all four RAM slots. You can eject the existing ram by pulling on one of two black strips, which should be tucked around the center of each column of slots. If the DIMM doesn’t release from a slight tug, don’t worry. It can take a firm, sustained pull to knock them out of place.
Now you’re ready to install the new RAM. The DIMMs should be installed in the top (towards the display) side first. If you’re installing two DIMMS, you can add the previously-installed RAM to the bottom slots to increase the overall memory even more. It’s a good idea to pair equal amounts of RAM side-by-side. For example, my iMac has two 4 GB DIMMs in the top slots and a pair of 2 GB DIMMs in the bottom. You’ll know the DIMM is installed correctly when you hear a clicking sound and the RAM is stable and even within the slot.
Once the RAM is installed, replace the black ribbon so that it covers the center of any sticks and tucks in the other side. The bottom panel should be replaced and the screws secured. The panel easily comes out of alignment during replacement, so the best way to do this is by loosely fitting each screw in place before tightening them all down.
After this is done, replace your iMac and start it up. If you receive any errors during startup, you may need to reseat the memory and make sure that the DIMMs you’re using are compatible with your Mac. You can check to see if the Mac recognizes the new RAM by clicking the little Apple in the upper-left corner of the screen and selecting About This Mac. If the amount of RAM listed matches what you should expect after the upgrade, you’re good to go.