Can you add 2X4gb memory alongside 2X2gb memory already installed on imac

Discussion in 'iMac' started by zombierunner, Jan 24, 2011.

  1. zombierunner macrumors 6502a

    Jan 18, 2011
    sorry for this question .. dont know much about these things .. the imac 27'' has 2X2gb memory ... if i was to buy 2X4gb (same spec ddr 3) .. then could i just add that to imac .. would it work - 2X2gb + 2X4gb = 12gb ram ... any compatibility issues with that?

  2. RichardBeer macrumors regular


    Jul 11, 2009
    I'm not sure how many memory expansion slots the current iMacs have but what I can tell you is that it is generally ill advised to mix your RAM sizes and speeds. Usually because-

    1) Mixing RAM sizes/brands can lead to instability issues.

    2) If you mix RAM speeds, then the faster memory modules will have to throttle their speeds down to match the slower RAM. Which is wasted performance.

    The best upgrade method if you want 12GB of RAM would be to go for 3x4GB sticks.

    Looking on the Apple site I would say that it also depends on your iMac size. The 21.5 inch models only have an option to be fitted with up to 8GB whilst the 27inch models can have up to 16GB, which would suggest that the 27 inch one has more space to fit in more expansion slots. So you'll need a 27inch and 3X4GB sticks for the safest upgrade path.

    That is providing we are talking about the latest iMac.
  3. The-Pro macrumors 65816

    Dec 2, 2010
    Both the 27" and the 21.5" iMacs have 4 RAM slots.
    So yes u ca upgrade to 12gb (2x2+4x2) 16 Gb is the maximum (4x4gb)
    that vid shows you how

    The option apple gives u to upgrade RAM to 8Gb in the 21.5" model are 4x2Gb RAM modules. so 4 slots :D
  4. DanielCoffey macrumors 65816


    Nov 15, 2010
    Edinburgh, UK
    If your iMac has 4 slots, then yes you can have 2x2Gb and 2x4Gb for 12Gb providing you keep them in their pairs (2,2 and 4,4 rather than 2,4,2,4) and the spec of your new 2x4Gb match the memory the iMac can use. List your exact model and folks here can advise what type of ram you need.

    Find your model in About this Mac, More Info, Hardware, Hardware Overview, Model Identifier. Your current memory will be listed under About this Mac, More Info, Hardware, Memory. You need to match the Type and Speed.
  5. John T macrumors 68020

    John T

    Mar 18, 2006
    All latest versions of the iMac take up to 16 GB of memory. They all have 4 RAM slots. There is no reason why you shouldn't add RAM as you originally suggested. The most important thing to bear in mind is to buy RAM sticks that are to the specification as originally installed in your machine. Look in :apple: > About this Mac > More info... > memory.
  6. philipma1957 macrumors 603


    Apr 13, 2010
    Howell, New Jersey
    i own a 2009 iMac a c2d 3.06ghz a 27 inch. When I purchased it last feb 2010 4gb ram sticks were very expensive .. i hace tested my imac with one 1gb stick in each of the four slots
    1 e e e
    e 1 e e
    e e 1 e
    e e e 1

    then a 2gb stick in each slot
    2 e e e
    e 2 e e
    e e 2 e
    e e e 2

    then a 4gb stick in each slot
    4 e e e
    e 4 e e
    e e 4 e
    e e e 4

    then combos of 1 and 2 and 4 gb sticks i ran xbench and geekbench and aja and day to day tests surfing the net and a lot of eyetv and netfilx.

    i never crashed the iamc in any combo i tried . higher ram won 16 gb got the best scores 14gb the next 13 gb the next 12gb the next 11gb the next. matched pairs were not needed and sometimes did not get the best scores.
    this was not on a quad core a dual core. so just buy thr right sticks ddr3 1066 for imacs from 2009 etc.
  7. rb5505, Jan 31, 2011
    Last edited: Jan 31, 2011
  8. runandsurf09 macrumors newbie

    Apr 19, 2009
    I have the i5 quad core 27" iMac and have 12 gb of ram in the same way you describe. I have not had a single issue with my computer since doing this.
  9. aussie_geek macrumors 65816


    Apr 19, 2004
    Sydney Australia

    Nope - WRONG!!

    Mixing RAM sizes/brands can lead to instability issues. - No - as long as Voltage and speed are the same.

    You always want an even number of sticks in your iMAC - 2 or 4.

    You can mix the densities. Just make sure you have the 2 x the same density in each bank.

    eg 2 x2GB or 2 x 4GB or 2 x 8 GB - bank A
    with 2 x2GB or 2 x 4GB or 2 x 8 GB - bank B


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