How to Upgrade the RAM in Your iMac


If you are cash-rich and time-poor, Apple will allow you to configure your Mac with more memory… at a cost. A pretty steep cost. For the rest of us, there’s the DIY route, which can end up saving a bundle and perhaps even endowing us with a sense of warmth and fulfillment.

Before We Begin

Generally speaking, Macs come pretty well equipped in terms of memory, with most modern Macs shipping with a minimum of 4GB. Still, increasing the available memory will allow you to comfortably run more programs simultaneously and can contribute to the efficient performance of your machine.

This article uses an iMac 27” late–2009 as an example. The standard onboard memory is 4GB and the machines can be upgraded to 16GB. The procedure for the 21.5” and 27” late–2009, mid–2010 and mid–2011 models is the same, though the memory specification is different.

Use Small Outline Dual Inline Memory Modules (SO-DIMM) that meet all of these criteria:

iMac (Late 2009) PC3–8500 Unbuffered Nonparity 204-pin 1066MHz DDR3 SDRAM
iMac (Mid 2010) PC3–10600 Unbuffered Nonparity 204-pin 1333MHz DDR3 SDRAM
iMac (Mid 2011) PC3–10600 Unbuffered Nonparity 204-pin 1333MHz DDR3 SDRAM

Alternatively, the easy way is to visit a supplier such as Crucial and use their memory finder tool to determine the correct memory for your Mac.

Once you have ordered and received the correct memory, we are ready to begin.

Step 1. Prepare Your Workspace

Tip: Follow anti-static precautions by, at the very least, grounding yourself on a radiator or piece of earthed equipment and by handling the memory carefully and holding only the sides and not the contacts or components.

Before we whip off the cover and swap the chips, take a few moments to properly prepare your workspace.

  1. Have a clear up of all the clutter around your Mac to create a clear working area.
  2. Turn off your Mac and unplug the AC power cable. Disconnect any or all of the ethernet, Firewire, USB, DisplayPort and audio in/out cables.
  3. Apple recommends that you leave ten minutes to allow the machine to cool down.
Clear your Desk
Before you begin, ensure you have a tidy work area.

Step 2. Position your iMac

There are then two ways in which you can approach the installation of memory. The first is the officially recommended Apple way: to lay your iMac, face down, on the desk.

  1. Lay a clean towel, cloth or other soft covering across your desk or other flat-surface workspace. This will be used to protect the screen.
  2. Carefully lay your iMac face down on the towel or cloth, with the base facing you.
Carefully lay your iMac, face down, on a towel or cloth (to protect the sceen
Carefully lay your iMac, face down, on a towel or cloth (to protect the sceen

Or, the second is the cheat’s way: to move your iMac to the front edge of the desk.

  1. Reposition your iMac towards the front edge of your desk, or work surface, and tilt the screen back as far as it will go.

Step 3. Access the Memory Compartment

The memory compartment is located at the base of the screen, in the middle, below the Apple logo on the front of your iMac. It is secured with three Philips captive screws. This means that when you unscrew the screws they will not come all the way out but will be retained on the memory compartment cover.

  1. Unscrew the screws that secure the memory compartment cover.
  2. Place the memory compartment cover aside in a safe place.
Accessing the memory compartment by removing three screws on the cover.
Accessing the memory compartment by removing three screws on the cover.
  1. Pull the looped flexible plastic strips out to reveal a tab.
  2. If you need to remove the existing memory modules, gain purchase, with your finger and thumb, to safely release the memory.
Reveal the plastic tabs.  Pull these to release the memory modules.
Reveal the plastic tabs. Pull these to release the memory modules.

As you can see from the photo, it gets dusty in there. You may wish to invest in a can of compressed air and give it a short blast to clear the area of dust.

Step 4. Install The Memory Modules

  1. Insert the new memory modules into the existing slots, the gold contacts side innermost, and push home.

Tip: There is an offset notch in the module which means that it can only be properly inserted one way round. If you can not push the module home, remove it and rotate 180 degrees before reinserting.

  1. When pushing the module home, push first in the middle and then at each side before returning the the middle. It requires a firm push to ensure the module is fully home and the module should sit nice and flush with, not proud of, the aluminum. Firm push, but don’t force it.
  2. Relocate the memory compartment cover and screw the middle screw a couple of turns, then the outer screws, to ensure the cover is properly located. Tighten all screws in turn when you are confident cover is properly positioned. The cover should be absolutely flush with the surrounding case when properly fitted.
Inserting a memory module into an iMac 27".
Inserting a memory module into an iMac 27".

Step 5. Power Up

Now that you have installed your new memory modules, hook up your iMac to the AC Power cable and switch it on. If all has gone according to plan your iMac will boot in the normal way and you can log in as normal.

Oh no, my Mac won’t boot!

Tip: Most readers can skip this section, but it’s worth knowing what’s wrong when your iMac won’t boot after installing new memory

When your iMac starts up it goes through a procedure known as POST, or Power-On Self-Test. If you receive a tone on start up this is telling you that there is a problem. By listening to the tones, you can determine the problem:

One tone, a five-second pause, repeat: means that there is no RAM installed. You will need to check that you pushed those modules into place properly - it’s an easy mistake to make.

Three successive tones, a five-second pause, three successive tones: RAM does not pass data integrity check. This means that there is a problem with your RAM. Do you have the correct specification memory? If so, contact your memory supplier.

One long tone when holding down the power button Firmware upgrade in process. See About firmware updates for Intel-based Macs for more details.

Three short tones, three long tones, three short tones (this is morse code for SOS): This means that a firmware restoration from CD in process. See About the Firmware Restoration CD (Intel-based Macs) for more details.

Step 6. Check Your Available Memory

We can easily check the installed memory in the iMac by clicking on the Apple icon on the top left of the menu-bar. Select About this Mac and then click on More info to reveal the following window:

Click on the Apple icon (top left of menu bar) and select 'About this Mac' then click 'More info'.
Click on the Apple icon (top left of menu bar) and select 'About this Mac' then click 'More info'.

The fourth option along, Memory, gives us more information:

Click on the 'Memory' tab (fourth one along) to reveal how much memory is installed in what sort of configuration.
Click on the 'Memory' tab (fourth one along) to reveal how much memory is installed in what sort of configuration.

In this example, the iMac has the maximum possible memory installed as four banks of 4GB.

Memory Upgrades for Other iMacs

For Succeeding Late–2012 “Skinny” iMacs

For succeeding late–2012 “skinny” iMacs, only the 27” model is easily user-upgradable in terms of memory. This is done through accessing the memory modules in the reverse of the machine and that procedure is not covered by this article. The 21.5” skinny iMac is, in practical terms, not easily upgradeable - so the advice would be to configure your iMac at the time of order from Apple - but that will prove to be an expensive pill to swallow.

For Preceding 20 & 24-inch Aluminium iMacs

For the preceding model range of 20 and 24-inch aluminium iMacs, mid–2007, early–2008 and early–2009, the procedure described above is largely similar with the exception of there only being one screw securing the memory compartment cover.

For Earlier White 17 & 20-inch Intel iMacs

For earlier white 17 and 20-inch iMac intel models — from early, mid and late 2006 — two screws secure the memory compartment cover and the memory is released using rigid plastic tabs on either side of the memory modules.

In all cases, the precise specification of memory will need to be determined for your machine. This can be done by using the Crucial memory checker tool.

All Done!

Provided you have followed the instructions correctly, you are now able to upgrade your iMac with more memory at a more competitive cost than if you had the memory upgraded with Apple’s build-to-order system.

Installing more RAM in your iMac is a cost-effective and simple way of improving the performance and efficiency of your Mac and, perhaps, eeking out a longer lifetime from the machine before you need to upgrade to a newer model.

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