question about iMac memory "pairing"

Discussion in 'iMac' started by John Paul, Sep 15, 2011.

  1. John Paul macrumors member

    Joined:
    May 10, 2010
    Location:
    Washington DC
    #1
    Just last night ordered one of the new 21.5" iMacs, which comes with 4 GB RAM standard (2 x 2GB). I know the iMac has 4 slots so am planning on upgrading the RAM once the computer arrives.

    My question is, is there any reason (other than the extra cost) why I wouldn't want to add (2 x 4GB) more, giving me 12 GB, rather than adding (2 x 2 GB), for a total of 8 GB?

    In other words, is there any "advantage" to having:

    2 GB
    2 GB
    2 GB
    2 GB

    Over having

    2 GB
    2 GB
    4 GB
    4 GB

    ??? Does my question even make sense? I guess it's a way of saying, if "paired" memory is good, is "quadded" (not a real word) memory better? Or as long as it comes in pairs, will more always be better than less?
     
  2. TMRaven macrumors 68020

    TMRaven

    Joined:
    Nov 5, 2009
    #2
    The iMac's motherboard supports dual channel memory. It is possible to get 2,2,2,2 in dual channel and possible to have 2,2,4,4 in dual channel as well. Just make sure each channel gets 2,4-- you want same amount of memory per channel.
     
  3. err404 macrumors 68020

    Joined:
    Mar 4, 2007
    #3
    2x2 + 2x4 is fine so long as you populate the banks correctly. Both memory stick in the same BANK should match in order to get dual channel support. The BANKs are arranged horizontally.

    Install it as:
    --2gb-- --2gb--
    --4gb-- --4gb--

    Do NOT install it as:
    --2gb-- --4gb--
    --2gb-- --4gb--
     
  4. AcesHigh87 macrumors 6502a

    AcesHigh87

    Joined:
    Jan 11, 2009
    Location:
    New Brunswick, Canada
    #4
    This

    I wound up only adding another 4GB to my new iMac to save a bit of money but adding 8GB will work just as well. I just plan on upgrading mine to the full 16GB when it becomes cheaper.
     
  5. shakyhand macrumors newbie

    Joined:
    Jan 14, 2011
    #5
    What if I have only 3 stick of 4gb ram and left 1 stick of original 2gb ram. will my iMac run properly with 14gb ram with this configuration?

    thanks
     
  6. TMRaven macrumors 68020

    TMRaven

    Joined:
    Nov 5, 2009
    #6
    It'll have 14gb of ram, but only 8gb will be in dual channel bandwidth.
     
  7. leman macrumors 604

    Joined:
    Oct 14, 2008
    #7
    The answer is "maybe". Combining RAM from different vendors is always a bit of a lottery. It may run, it may crash. Combining two different RAM blocks in paired slots is even more risky though, I suggest you avoid it.
     
  8. yusukeaoki macrumors 68030

    yusukeaoki

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    Mar 22, 2011
    Location:
    Tokyo, Japan
  9. shakyhand macrumors newbie

    Joined:
    Jan 14, 2011
    #9
    Yeah.. that's what I've been thinking.. My intention was to buy 2 stick of 4GB RAM yesterday. However, it was so damn cheap and I ended up with 3. However, I'm 300km away from my iMac now, cannot test the RAM until I get home tonight... if the RAM works, no doubt I'll get another one to make it 16GB..
     
  10. yusukeaoki macrumors 68030

    yusukeaoki

    Joined:
    Mar 22, 2011
    Location:
    Tokyo, Japan
    #10
    2x4GB are really cheap only like 30 bucks off newegg.
    Just make it 60 bucks and you get 16GB!
     
  11. err404 macrumors 68020

    Joined:
    Mar 4, 2007
    #11
    Sure, but the question is; does 16GB result in any tangible improvement over 12GB. If not, your throwing away $30 on bragging rights.
     
  12. philipma1957 macrumors 603

    philipma1957

    Joined:
    Apr 13, 2010
    Location:
    Howell, New Jersey
    #12
    well look at your activity monitor if you have a lot of page outs with 12gb rm then 16gb ram will speed you up if you have a hdd. if you run your osx off an ssd the ram is less important. every page out means you used your hdd instead of ram. some users can actually put in 32gb ram and be short ram of course they are few and far in-between. I need around 9gb or

    10 gb to avoid paging out but ram was cheap and i have 16gb. as my iphoto just keeps growing i will need it one day.
     
  13. shakyhand macrumors newbie

    Joined:
    Jan 14, 2011
    #13
    I will be doing a lot of video and photo editing (FCP X and photoshop CS5). Got a lot of 8mm tapes stuck in a drawer for the last 16 years and a new AVCHD video. Have been into photography since 2006 with a Canon 7D and a handful of red ring canon lenses..(another money wasting hobby).. Hopefully, the 12GB is enough..
     
  14. AcesHigh87 macrumors 6502a

    AcesHigh87

    Joined:
    Jan 11, 2009
    Location:
    New Brunswick, Canada
    #14
    I can run both PS CS5 and FCP X without any trouble and I only have 8GB of RAM. 12 Should work fine. The full 16 would run better, mind you, but 12 should do it.
     
  15. John Paul thread starter macrumors member

    Joined:
    May 10, 2010
    Location:
    Washington DC
    #15
    First, thanks to all who replied so far.

    But I am confused about "banks" because if I am reading this right, the 4 GB of RAM that came pre-installed by apple on the iMac in my office (21.5", bought new this January) is not properly paired (!?!)

    Directly from System Profiler:

    BANK 0/DIMM0:

    Size: Empty
    Type: Empty
    Speed: Empty
    Status: Empty
    Manufacturer: Empty
    Part Number: Empty
    Serial Number: Empty

    BANK 1/DIMM0:

    Size: Empty
    Type: Empty
    Speed: Empty
    Status: Empty
    Manufacturer: Empty
    Part Number: Empty
    Serial Number: Empty

    BANK 0/DIMM1:

    Size: 2 GB
    Type: DDR3
    Speed: 1333 MHz
    Status: OK
    Manufacturer: 0x80CE
    Part Number: 0x4D34373142353637334648302D4348392020
    Serial Number: 0x8125BBB5

    BANK 1/DIMM1:

    Size: 2 GB
    Type: DDR3
    Speed: 1333 MHz
    Status: OK
    Manufacturer: 0x80CE
    Part Number: 0x4D34373142353637334648302D4348392020
    Serial Number: 0x8125BA91


    So what they heck is that about? If I am reading this corrctly, then rather than pairing those two RAM modules in the same bank, they put one in one bank and one in the other. Which would mean if I were to add 2 more modules to this computer (let's say 2 x 4 GB just for discussion), it wouldn't simply be a matter of adding them to the two slots currently free?

    Thought I understood things, but now am more confused than I was before.
     
  16. AcesHigh87 macrumors 6502a

    AcesHigh87

    Joined:
    Jan 11, 2009
    Location:
    New Brunswick, Canada
    #16
    If you opened the RAM panel you'd see what they mean, trust me. Essentially though there are 4 slots in the iMac for RAM but two banks. A bank is a pair of horizontal slots, one stick of RAM in each. What comes pre-installed is a 2GB stick on both top slots, thus both in the top bank. System profiler just lists is oddly. There will be two open slots for new RAM in the bottom bank. You can either add two sticks in there or remove the ones pre-installed and add 4 new sticks. In theory you could remove the apple RAM and pop in new ones in bank 1 but it would serve no purpose.
     

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