Is is OK to mix RAM modules in a 4-slot 21.5" iMac?

Discussion in 'iMac' started by DHart, Jul 14, 2010.

  1. DHart macrumors 6502

    DHart

    Joined:
    Jan 17, 2008
    #1
    I've got a refurb 21.5" iMac 3.06GHz/4GB RAM/500GB HDD arriving soon.

    I believe it has two 2GB modules installed in two of the four memory slots, with two other slots unused. I have a few questions before I order more RAM for my machine.

    Is it advisable to have ALL the RAM modules be of identical brand and size?

    Can other brands of RAM be added to the two empty slots as long as they are of the same specifications?

    Do RAM modules need to be added in pairs or is single ok?

    Can the added RAM modules be of any size (1GB, 2GB, or 4GB) and still work fine with the factory installed 2GB modules?

    For example, would there be any performance problem by adding a single 4GB module to the existing two 2GB modules? Or would it be better to add two 2GB modules rather than a single 4GB module?

    Thanks, in advance, for the help.
     
  2. jav6454 macrumors P6

    jav6454

    Joined:
    Nov 14, 2007
    Location:
    1 Geostationary Tower Plaza
    #2
    iMacs use SO-DIMMs, so they have to be that or they won't fit. (SO-DIMM are for laptops while DIMMs are for desktops)

    You have to be sure of memory speed also. iMacs use 1066MHz DDR3 memory.

    As per capacity and vendor, you can use any kind your heart desires. Try to have matching capacities tho (2x2GB or 2x1GB or 2x4GB) as that gives you faster dual channel goodness.
     
  3. dexthageek macrumors 6502

    Joined:
    Dec 7, 2007
    #3
    As long as the RAM is CAS7 it really doesn't matter.

    If you have a late-2009 model 21.5, your machine should have 2x2GB, leaving 2 empty slots.

    http://eshop.macsales.com/shop/memory/iMac/DDR3_21.5_27
     
  4. DHart thread starter macrumors 6502

    DHart

    Joined:
    Jan 17, 2008
    #4
    So, as long as I use SO-DIMM 1066MHz DDR3, I can mix and match brands and capacities no problem... great.

    Just to clarify, though, the iMac already has two 2GB modules for 4GB total. And I think I want to go to 8GB.

    If I add a single 4GB module, that still leaves another slot to use later, if I want to.

    Or would I definitely benefit from having each of the four slots in the machine filled with a 2GB module so they all match, capacity-wise?

    If there is a speed benefit to having all match, might that be worth it? Or not enough to notice?
     
  5. Hellhammer Moderator

    Hellhammer

    Staff Member

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    Dec 10, 2008
    Location:
    Finland
    #5
    If you had 4x2GB or 2x2GB + 4x2GB, both pairs would be running in dual-channel mode but that's not what you should worry about, it's unlikely that you will notice any difference. I've seen plenty of people with 2x2GB + 1x4GB and they have had zero issues.
     
  6. DHart thread starter macrumors 6502

    DHart

    Joined:
    Jan 17, 2008
    #6
    Is it important to match capacity across all four slots? Or just to match top slots capacity to each other and bottom slots capacity to each other?

    I don't understand the dual-channel thing you guys have mentioned.

    Like, for example, two 2GB modules in the top slots and two 4GB modules in the bottom slots (for 12 GB total)?
     
  7. Hellhammer Moderator

    Hellhammer

    Staff Member

    Joined:
    Dec 10, 2008
    Location:
    Finland
    #7
    Don't worry about dual-channel, it's overrated. It's unlikely that you will notice difference between single- and dual-channel as most apps can't even saturate the 68.2 Gbit/s (8.525 GB/s) data rate of single-channeled 1066MHz DDR3, let alone the doubled data rate what dual-channel brings.
     
  8. Abs1nth3 macrumors newbie

    Joined:
    Jul 12, 2010
    #8
    Yes, this would work fine. As long as the pairs are matching you should be fine. They don't have to match but I would suggest doing it right and getting matching pairs of ram.
     
  9. DHart thread starter macrumors 6502

    DHart

    Joined:
    Jan 17, 2008
    #9
    OK cool... and I presume the "pairs" refers to the top two slots as a pair and the bottom two slots as the other pair.

    I'm half tempted to put 4's in the bottom two slots to make it total 12 GB, but I have a feeling that 8GB total will be more than plenty to speed my CS5 Photoshop and Lightroom work along quite nicely.

    Does the RAM help a lot with Final Cut Studio? If so, perhaps I should be going with 12 GB.
     
  10. Gregintosh macrumors 68000

    Joined:
    Jan 29, 2008
    Location:
    Chicago
    #10
    If you do HD video with Final Cut I would definitely recommend more RAM. When it comes to video editing, especially HD, there is no so such thing as having "enough RAM." ;-)

    If you can afford two 4 gig chips I'd say do it. Otherwise get one 4GB chip for 8GB total, and leave that one last slot available to upgrade again later when memory prices come down or when you really need it.
     
  11. DHart thread starter macrumors 6502

    DHart

    Joined:
    Jan 17, 2008
    #11
    Thank you for that. Makes perfect sense. I think I may just "go for the gusto" and order up two 4GB modules from OtherWorld or wherever.... I've never had more than 8GB of RAM in any of my many Macs, so to have 12 GB would be a milestone for me.
     

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