iMac maximum memory limit


macrumors newbie
Original poster
Jan 25, 2012
Hi - I bought a 24" iMac in Nov 2008 with 4GB RAM. I understand that this is the max. allowable memory, however I wonder if there's a way to get any more using something like a USB drive? This is possible in Windows I think and called something like MemoryBoost. Thanks for any suggestions!


macrumors Westmere
May 16, 2008
Your iMac can use up to 6GB of RAM.

You can find specs on all Apple products, including maximum RAM:
  • By visiting Actual Maximum RAM
  • By using Mactracker
  • By entering your serial number here to find specs for your model. (Be aware that some models can use more RAM than Apple shows. Check EveryMac or MacTracker to verify.)
Nov 28, 2010
That iMac has a 6 GB limit:

And know, that boosting your RAM via USB is horrible, as USB only offers 35 MB/s read/write speeds, while writing to the internal HDD can offer up to 110 MB/s read/write speeds and DDR2 RAM with 800 MHz has read/write speeds of 6400 MB/s, which is 58 times faster than the internal HDD and 182 times faster than USB 2.0, thus USB 2.0 would slow you down actually.


If it can, then perhaps you can sell existing 4 GBs Simms and replace with availble 6 GBs. Thus, memory upgrade to 6 GBs is more affordable...
While there are 4 GB DDR2 SO-DIMM modules, there are no 6 GB DDR2 SO-DIMM modules. To get to 6 GB RAM, one has to use one 2 GB and one 4 GB SO-DIMM module.

Have a look at Activity Monitor (Applications / Utilities /) and select All Processes and sort by Real Mem to see what the culprit consuming too much RAM may be.
Also check the "System Memory" tab to see what your "Page ins:", "Page outs:" and "Swap used:" are.

image below uses sorting by CPU as an example

Further reading: