This is always a popular question. “How much RAM (memory) do I need for my Mac?” In return I will ask you, how much you want to put in? Most current Mac models takes more RAM than you ever need (in most situation). A quick look at Activity Monitor will tell you does your Mac hungry for RAM. Look at the Page-out counts, if you have very high page-out (compare to page-in, for example, you have 1GB page-in, but your page-out is 800MB), it means you need to add more RAM for your Mac, or start cutting down running apps.

Now you know you need more RAM or not, the next question is how much your Mac can take? Few years ago, we basically just follow what Apple says on the spec sheet and we won’t goes wrong. But as we move on lately, many Mac models seems to take more RAM that Apple stated. And to make your shopping easier, I’ve compiled the list of total RAM a Mac can take based on models as follow (this only for Intel Macs):

MacMini
- Core Duo/Core Solo: 2GB (same as Apple spec)
- Core 2 Duo DDR2 model: 3GB (Apple says 2GB)
- Core 2 Duo DDr3 model: 4GB  (same as Apple spec)

iMac (white)
- Core Duo: 2GB (same as Apple spec)
- Core 2 Duo 1.83GHz: 2GB (same as Apple spec)
- Core 2 Duo >1.83GHz (late 2006): 3GB  (same as Apple spec)

iMac (alu)
- Core 2 Duo 2007-2008: 4GB (same as Apple spec)
- Core 2 Duo DDR3: 8GB (same as Apple spec)

MacPro
- Xeon 2006: 32GB (Apple says 16GB)
- Xeon 2008: 32GB (same as Apple spec)
- Xeon 2009: 32GB for 8-slots model, 8GB for 4-slots model (same as Apple spec)

MacBook (white & black)
- Core Duo: 2GB (same as Apple spec)
- Core 2 Duo (late 2006 – mid 2007): 3GB (Apple says 2GB)
- Core 2 Duo (late 2007-2009): 6GB (Apple says 4GB. you need 2GB+4GB. 2x 4GB wont work)

MacBook (unibody)
- Core 2 Duo DDR3: 6GB (Apple says 4GB)

MacBook Pro
- Core Duo: 2GB (same as Apple spec)
- Core 2 Duo 2.16GHZ & 2.33GHz: 4GB (Apple says 3GB)
- Core 2 Duo Mid 2007 – Early 2008: 6GB (Apple says 4GB)

MacBook Pro (unibody)
- Core 2 Duo 15″ 2.4/2.53/2.8GHz: 6GB (Apple says 4GB)
- Core 2 Duo 2.66/2.93GHz: 8GB (Apple says 4GB for 15″)

I hope this help to clear some doubt. Do let me know if I missed anything. For MacBook Air, memory are soldered. So you can’t do anything about it.