iMac "Core i5" 3.2GHz 27-Inch (Late 2012)

RAM stands for Random Access Memory, it is a short term store for data which is only used while the machine is in operation. This is not where your data and applications are stored (that's the Hard Drive or Solid State Drive) so RAM can be replaced without worrying about any data transfer issues.

How much RAM you need depends very much on what you are doing with your Mac. Adding more and more RAM does not necessarily speed your machine up - rather the better way to think about it is that not having enough RAM will slow you down. When your system runs out of physical memory it will use virtual memory on your hard drive instead, this is orders of magnitude slower than RAM, and will result in more instances of the spinning wheel or stuttering.

The more RAM you have, the more things you can do at once and you are able to switch between them better. Also as later operating systems come along they have greater requirements, so a machine feeling fast running OSX 10.7 with 4GB of RAM may well feel sluggish in OSX 10.10 with the same.

Here are the amounts of RAM we have found to be the real minimum for comfortable use in different operating systems. The minimum levels here are not absolute, but even lighter users will be well advised to take steps to minimise RAM use (principly restricting the number of applications they use simultaneously) if they are below them. Of course for some more specialist users of RAM intensive applications, even the ideal amounts listed will be grossly inadequate.

• Mac OSX 10.6 Snow Leopard - Min 2GB, ideal 4GB or above
• Mac OSX 10.7 Lion and 10.8 Mountain Lion - Min 4GB, ideal 6GB or above
• Mac OSX 10.9 Mavericks,10.10 Yosemite, 10.11 El Capitan - Min 6GB, ideal 8GB or above
• macOS 10.12 Sierra and Later - Minimum 8GB, and this is generally reasonable for light usage though 16GB is more comfortable.

Some systems may not be able to use these amounts but will still run the newer OSs, in these cases maximising your RAM will be the best you can do. To get a better idea of your own specific RAM requirements, you can use the Activity Monitor utility built into macOS. This will let you see how much RAM you really need while using your Mac in the way you use it. Activity Monitor is inside your Utilities folder, which is inside your Applications folder. Apple have an in-depth explanation of how to use Activity Monitor here.

There are lots of different types of RAM. The RAM modules and compatability information below was generated from the Serial Number or Model ID you selected, and is guaranteed to work 100% or your money back. Even if your manual says otherwise! Original manuals, and even online documentation, are not updated after a machine is released and therefore not up to date with the actual maximum RAM that can be used. Many machines can make full use of more RAM than the offical spec, and we guarantee that the maximum amounts we list will work flawlessly, and be fully utilised by your Mac.

The hard drive or solid state drive is where all your documents, data and applications are stored permanently. Below this box are all the drives we do that are guaranteed 100% compatible with this Mac, based off the Serial Number or Model ID that you have selected.

The list below is divided into sections for the main types of drives, which can include:

• Solid State Drives (SSDs) - large chunks of Flash memory used for storage, the fastest and most reliable option, but also the smallest and most expensive.
• Hard Disk Drives (HDDs) - the standard rotational drives used in older Macs. Big and cheap, but much slower than SSDs and subject to mechanical failures that do not effect SSDs. These have a spin speed measured in Revolutions Per Minute (RPM), with higher numbers being faster operating drives.

For more details on the differences between these drives, please see this post on our blog.

With most Macs there are lots of options for having more or faster storage, and many can take multiple drives so you can mix and match SSDs and rotational hard drives to find your ideal combination of size, speed and budget. Some Macs have more than one main drive bay, and many Macs can use our range of caddies to replace their DVD drives with additional hard drives or SSDs. Some Macs also have additional drive bays that can be used with a mounting kit. If you have multiple types of bay in this Mac, you can select them with the grey tabs below this box.

It is very important with all system drives (that is, a drive that you boot from) to leave a good amount of free space to allow the system to work well. We recommend leaving around 20-30GB of free space on the system drive, The closer you get to full on your system drive, the slower the Mac will perform.

A 1TB drive can hold:

• Up to 1,000 hours of digital video
• Up to 250 two-hour DVD films
• Up to 320,000 digital photos
• Up to 16,660 hours of digital music

All drives come blank and will need to be formatted (erased), and if they are to be a boot drive, have an operating system installed. There are a variety of ways of restoring your data, either through time machine or by cloning. We sell drives, tools, enclosures and cables for you to do the work at home (see the "Cables, Adaptors & Tools" tab above), or you can send/bring your machine to us for us to do the work - prices all below. However you do it, you can be sure you are getting the correct part with our 100% compatibility guarantee.