RAM

Discussion in 'iMac' started by massy72, Aug 13, 2017.

  1. massy72 macrumors newbie

    massy72

    Joined:
    Jul 11, 2017
    #1
    Hi,
    I have new Imac 2017 with i5 3.5-575-512-16GB

    Question about RAM
    I have purchased this one and I'm waiting the shipping.....
    Crucial 16GB Kit (2 x 8GB) DDR4-2400 SODIMM Memory for Mac
    DDR4 PC4-19200 • CL=17 • Single Ranked • x8 based • Unbuffered • NON-ECC • DDR4-2400 • 1.2V • 1024Meg x 64 • lead free • halogen free • for Mac


    My Mac have Apple 16 GB of RAM (8+8) so occupied 2 slot
    I don't have opened the rear flap and I don't know how this RAM is located into the slot (Maybe 1&2 or 1&3)

    When I installed the Crucial RAM I must to change the sequence or I can put inside in any free slot?

    Thank you so much

    Max
     
  2. redheeler macrumors 603

    redheeler

    Joined:
    Oct 17, 2014
    #2
    Simply instal the new RAM into the free slots.
     
  3. Ledgem macrumors 65816

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #3
    You're correct to question this, because if you mix RAM modules then you'll lose out on dual channel functionality and if your purchased RAM is faster than the RAM that came with your computer, it'll be forced to run slower.

    When I upgraded my iMac I did it interleaving (RAM pair #1 went into slots 1 and 3, pair #2 went into slots 2 and 4) but I can't find out where I read it... and I ended up buying a second set of identical RAM, so when I check my memory configuration in "About this Mac" it all looks the same.

    But that might be the best solution. Go to the Apple menu > About this Mac > System Report... > Memory.

    You should have four slots: BANK 0/DIMM 0, BANK 0/DIMM 1, and BANK 1/DIMM 0, BANK 1/DIMM 1.
    You want the memory to be in the same bank. So if you're currently seeing either Bank 0 or Bank 1 full, then as redheeler suggested, just install your new RAM into the empty slots.

    If it's currently showing RAM in bank 0 and bank 1, then you may need to move one of the original sticks. Where to move it will involve a bit of guesswork, but here's how I'd do it. If the DIMMs are currently in slots 1 and 2, then I'd move one from slot 2 to slot 3. If they're in 1 and 3, then I'd move the stick in slot 3 to slot 2. Then fill in the empty slots with your RAM from Crucial.

    Hope it helps.
     
  4. massy72 thread starter macrumors newbie

    massy72

    Joined:
    Jul 11, 2017
    #4
    The RAM that I have purchased have the same CL of Apple RAM.... it's full compatible
    This is my situation..

    Schermata 2017-08-16 alle 11.07.41.png

    So you think it's better to move the Apple RAM from BANK1/DIMM0 to BANK0/DIMM1??

    Sorry.... my system is in Italian language :)
     
  5. Ledgem macrumors 65816

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #5
    Yes, that is what I would recommend. If the RAM you purchased has all of the same specifications as the RAM that came with the computer it may not matter, but you have a lower risk of incompatibility if you have perfectly matched RAM sticks.
     
  6. SaSaSushi macrumors 68040

    SaSaSushi

    Joined:
    Aug 8, 2007
    Location:
    Takamatsu, Japan
    #6
    Just put the new Crucial RAM into the empty slots as redheeler already recommended above. The Apple stock RAM is already installed in dual channel configuration. Leave it be.

    With the Mac you want to have matching RAM sets in alternating slots (DIMM0 and DIMM1).
     
  7. Ledgem macrumors 65816

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #7
    Based on the screenshot that he posted, it looks like the RAM didn't come installed in a dual-channel configuration (he has one DIMM in Bank 0 and another DIMM in Bank 1). He'll need to move one of the original DIMMs before he can install his new RAM, if he wants to have everything running as fast as it can go.
     
  8. SaSaSushi macrumors 68040

    SaSaSushi

    Joined:
    Aug 8, 2007
    Location:
    Takamatsu, Japan
    #8
    Proper dual-channel configuration on the iMac means matching modules in DIMM0 and DIMM1. This has been proven by both benchmarks which show severely decreased performance with matching module sets in BANK0 and BANK1 as well as CPUZ in BootCamp Windows which confirms dual channel enabled only with matching sets in DIMM0 and DIMM1.
     
  9. Ledgem macrumors 65816

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #9
    I tried to do a search but couldn't find anything supporting what you mentioned; by any chance, do you have links? I know how annoying it can be to find something you saw weeks, months, or even years ago, though; if you can't easily find it, no worries.

    The reason that "matching DIMMs" (as opposed to matching DIMMs to Banks) doesn't make sense to me is because DIMM refers to the RAM module, itself (DIMM standing for "dual in-line memory module"). Apple is designating two memory banks in the iMac, with two DIMMs per bank. Unless the terminology is skewed in some way, the bank should thus refer to the two memory modules that are paired. It doesn't make sense to have DIMM 0 in Bank 0 match DIMM 0 in Bank 1, because the banks are where the grouping is occurring. If that's incorrect, then what does "Bank" refer to?

    I suppose another reason I'd like to see the original data for myself is because the performance difference between operating in dual-channel and single-channel mode is generally regarded as being not overly significant; most people cite only a few percentage points. I'm the type of person who likes to have optimal performance (particularly if I've already paid for it and it's just a matter of swapping some components around), which is why I keep replying, but it means that @massy72 shouldn't suffer a hit to performance even if the RAM isn't operating in dual-channel mode.
     
  10. SaSaSushi, Aug 17, 2017
    Last edited: Aug 17, 2017

    SaSaSushi macrumors 68040

    SaSaSushi

    Joined:
    Aug 8, 2007
    Location:
    Takamatsu, Japan
    #10
    I am basing this on my own benchmark results but others in these forums have also confirmed it. Not only do benchmark results improve noticeably with matching sets in DIMM0 and DIMM1 as opposed to BANK0 and BANK1 but running CPUZ in BootCamp Windows shows dual channel enabled only when it is configured that way and not when it is in matching banks. Then there is the fact that Apple ships the iMac with their matching sets in DIMM0 as well.

    I will get a screenshot from CPUz later and post it to this thread. I like optimal performance as well.

    Dual channel alone probably wouldn't affect performance so much but my best guess as to why my benchmarks show such a marked difference is that with matching modules in BANK0 and BANK1 you are actually using mismatched sets in the same channel. If all of the modules are identical then it probably wouldn't make much of a difference at all. However, in my case I have 2x16GB of Crucial Ballistix Sport LT CL16 RAM and 2x8GB of Apple stock CL17 RAM and when the Ballistix and Apple modules are forced into the same channel with each other the benchmarks show it.
     
  11. Ledgem macrumors 65816

    Ledgem

    Joined:
    Jan 18, 2008
    Location:
    Hawaii, USA
    #11
    Indeed, I ended up skirting the issue by using four of the same RAM modules, and unfortunately there doesn't seem to be a way to verify dual channel operation within macOS. Thanks for offering to check in CPUz to set the record straight.
     

Share This Page