Its actually harder to find out than you think! You either get Crucial links, Apple.com links or Macrumors. Any other links that may seem promising just seem to mention memory but aren't actually selling it. I'm after 8GB for my Thunderbolt iMac. Crucials website won't work on my computer. If you click buy now it simply reloads the page. I've been trying for days. I've called but I'm on hold forever, as soon as I mention it to 'live chat support' the other person stops responding and I've emailed them last week and still have yet to get a response so it seems they don't want my money.