What RAM for RevB iMac??

Discussion in 'Macintosh Computers' started by arklab, May 3, 2005.

  1. arklab macrumors member

    Feb 26, 2005
    This is my first Mac, and I could sure use some help form experienced iMac users.
    I will be buying a new (RevB) iMac G5 this afternoon with some aftermarket DDR RAM (two 1M sticks of DDR400).
    While I am familiar with Wintel requirements in CL ratings, the move from 600 to 667 FSB in the revB has me worried.

    The "rev A" iMac machine was quite happy with the CL (CAS-to-RAS) of 3 (the slowest and cheepest) memory.

    But with the faster 667 FSB of the rev B iMac, would through-put be helped by a CL of 2.5 or even 2.0? :confused:

    Newegg has Roswell 1M sticks on sale today for only $79 ($158 for a pair), but they are only CL 3.0.

    Your advise please . :)
  2. arklab thread starter macrumors member

    Feb 26, 2005
    (shameless bump)

    Comon, guys!
    Somebody must know? :(
  3. akelley macrumors newbie

    May 3, 2005
    Memory type and installing 2 different sizes?

    Yes, I would like to know this as well. I just purchased my first Mac (20" iMac) and want to upgrade the memory via 3rd party RAM (I would like to add a 1GB stick). On another board, someone mentioned that you shouldn't mix memory sizes (i.e., 512MB and a 1G stick). I read the instructions for installing RAM from the Apple site and it doesn't mention anything about installing memory in pairs - it just said that either slot can use 256MB, 512MB, or 1GB sticks of PC3200 400Mhz DDR.
  4. arklab thread starter macrumors member

    Feb 26, 2005
    OK, from what tests I have read done on the Rev A iMacs (and also from Wintel machines):
    1) The current processor/memory controler is not of a dual-channel design.
    2) Although benchmarks show improvement with a mached pair of DIMMs, realworld apps don't.
    3) Anyone, on any computer system, who wants to assure maximum benifit from more than one DIMM will Use all DIMMs of the same size, type, timeings, manufacture/brand, and batch which were purchased from the same store at the same time.

    Anything else will probably work, but may well slow down your computer .
    Memory conflicts and problems are also the hardest to find and fix.

    And I still don't know the optimum timeings for the new 667 FSB to use! :eek:
  5. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    The iMac G5 uses the same memory architecture as the previous rev. -- that is 64 bit access, slots can take RAM individually. The 128 bit access option with two matched DIMMs may make a marginal difference in speed, but may not.
    "If only one DIMM is installed, the memory bus is 64-bit. If two non-identical DIMMs are installed, there are two 64–bit memory buses. If two identical DIMMs are installed, the memory bus is 128-bit. Identical DIMM pairs have the same size and composition and provide the fastest and most efficient throughput."


    Apple has previously stated that CAS Latency doesn't make a difference in speed, but the new iMac dev notes don't comment one way or the other
    "The iMac G5 supports CAS latencies of 2, 2.5, 3, 4, and 5."

    As far as the NewEgg budget RAM goes, I'll say again; choose RAM from a vendor who gives a guarantee of compatibility with your Mac. Buy PC Generic at your own risk of time and money.
  6. arklab thread starter macrumors member

    Feb 26, 2005
    If CAS of 2.0 is supported, it may be advisable to try it.
    And now that you mention, with the switch to the 64bit Tiger, I wonder if paired memory's 128 bit bus might not really begin to show more of an advantage?

    As far as NewEgg "budget" goes, it is not "generic", but branded.
    Just last year Patriot ram was considered "low-end generic" by some ... until AnandTech and others tested it and discovered it out proformed Kingston, Crucial, Corsair, and others.
    OCZ was at one time junk, but now is an industry leader.
    Buying from a quality company that will accept returns if something doesn't work is perhaps the best safeguard.
    Unless, of course, for maximum safety (but NOT necessarily proformance) and maximum high price, then Apple really can't be beat.
    I understand they even include instructions and the proper screwdriver to open the iMac case. A very nice touch, indeed!
  7. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Not arguing that the (Patriot, OCZ, whatever) RAM isn't quality RAM, but the risk you take is compatibility. The iMac G5 is the most finicky machine Apple currently makes, lots of PC3200 models do not work in it.

    Yes by all means make sure the company will take it back without restocking charges, but you'd still be out the shipping cost 2 ways and the week or two it takes to sort out. It doesn't make sense to me to take that risk to save $10. (Compared with Data Memory Systems, RamJet, OWC or other Apple-knowledgeable sellers)

    I don't see any benefit to CAS Latency 2 RAM -- 1 Gb CL2 modules are disproportionately expensive. Apple doesn't say whether the motherboard will adjust itself to take advantage of the lower latency (a la Intel P.A.T.), just that the RAM will function. My unsubstantiated guess is that the Mac simply runs all RAM at CL 3.0.

    PS: do NOT try to install RAM with heat spreaders -- you'll break the RAM socket because there isn't room physically in the iMac G5.
  8. arklab thread starter macrumors member

    Feb 26, 2005
    Thanks for the warning! It may help other Macnewbies, too.
    I was aware of the incompatability problem (I think it may have been discovered by BareFeats?), as I recall quite a few brands of ram (obtained from Apple aware shops) that had worked perfectly in PowerMac G5s flat would not allow the iMac to even boot!
    However if Apple has not completely solved that problem with this completly new motherboard (err, excuse me, "midplane") with a new memory controller, it will be not only my first Macintosh but my last as well! :mad:
    Time will tell.

    And as to saving $10, I'd agree if that were true.
    But the fact is I can get two 1Mb DIMMS for the price of one 1M DIMM upgrade on my order, and I get to keep the 512M DIMM as well.

    I believe that this is going to be the perfect computer for my mother as well, and I can upgrade her machine to a gig for nothing.

    Please correct me if this no longer holds true, but I always felt that if you wanted your computer (ANY computer ) to run smoothly, the buyer should take the recomended minimum and double it. ;)

    Anyway, it looks like my 17" superdrive will not be shipping for another week (the 11th - my wife really wanted the wireless keyboard, so BTO it is.), so maybe more test based info will come to light by then.

    Oh, and I just learned today that Apple shipping policy requires a person to sign for the delivery.
    I don't suppose (since I have to work) any of you good fellows would be willing to be here if I gave you the address, would you?
    Of course I understand your privacy must be protected, so I won't ask you real name. :p
  9. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Wasn't comparing third party with Apple, was comparing NewEgg or Fry's PC Generic unknown quantity RAM with a Mac-friendly seller like Data Memory Systems - that's the $10 spread.
  10. NevadaJack macrumors 6502

    Mar 8, 2005
    Las Vegas, NV
    I went to the Crucial site...used their Finder for the 2.0 20" iMac and ordered 1GB stick for $145. It will be here Friday. Did the same with my 17"PB when I got it. Works fine and guaranteed. Not worth playing games with who has the lowest price.

    My order is in manufacturing and hopefully be shipped by Friday.
  11. killuminati macrumors 68020


    Dec 6, 2004
    I am going to be getting the new iMac and I was considering buying 3rd party RAM. But I have decided that I will just spend the extra money and but it from apple. Then I know that I definately wont have any problems. :)

    And now to upgrade to 1gb of ram is only $150.
  12. Chip NoVaMac macrumors G3

    Chip NoVaMac

    Dec 25, 2003
    Northern Virginia
    What would you suggest for buyers that want to do a BTO with the Apple 1GB option, and do a future upgrade down the road, in order to get a matched pair?
  13. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Basically it can't be predicted. Even if you buy Apple RAM 1 month from now, you may get a different design of module with different chips.

    If you want to take the chance, you could pull the Apple 1 Gb and then call around to see who has a Samsung, or Hynix or Elpida or Micron module of the same model number. But sellers aren't going to take back a good module without a restocking charge just because it didn't play at 128 bit with your existing one.

    Also, Apple doesn't specify what constitutes a match - "identical ... size and composition" -- obviously the number and density of chips, the CAS Latency and the Row and Column organization of the banks will have to match, but we don't know what else.

    The only guarantee is to buy the 2 RAM modules together at one time, and sell off the Apple module.
  14. arklab thread starter macrumors member

    Feb 26, 2005
    With this I agree.

    And it gives lie to Apple consistency (not quality, consistency).
    Apple is saying that any ram that meets their basic specifications will work. Not work best, or fast. Just work.

    And that does not account for timings.
    I doubt they even bother to test every brand with every model of Mac, and they may be using what we call "generic" themselves. Price and availability change far to often in the memory market.

    And this is why I feel you might as give well try 3rd party ram. The mac-friendly online stores I've checked are also NOT specifing brand, timings, or that their memory will run the best for an iMac G5, just that the machine will run.
    Not suprising, as Apple makes no other claims, ether.
  15. paradillon macrumors member

    Jan 1, 2004
    possible to confirm 128bit performance?

    Once you have the add'l ram installed is there a way to confirm you are getting 128 bit performance? If you can't tell then for most people this is much ado about nothing. :rolleyes: But I'm still trying for the 128bit!
  16. Platform macrumors 68030


    Dec 30, 2004
    So let's say that someone has an iMac and it has the 1 512MB DIMM in it....but then they buy a 1GB stick from somewhere like Crusial or Kingston....would that be slower than the pervious.......if so then we need to throw out one and install two new or buy directly from apple :confused: :mad:
  17. monty77 macrumors 6502a

    Mar 4, 2005
    UK, South Coast
    I bought from Crucial too .... 2 x 1Gb sticks - not the cheapest but their support/warranty is 2nd to none and I know it'll work 100%.

    ...I am not interested in spending £1200 on a computer only to suffer sporadic memory/crash issues just because I chose to save a few £ on RAM.

  18. Savage Henry macrumors 65816

    Savage Henry

    Feb 20, 2004
    in a one horse, two house, three pub town.
    That is exactly what I did....
    Although I have yet to try it with serious memory/processor rendering stuff etc, the speed bumps in the applications I've used thus far are noticeably rewarding.
  19. paradillon macrumors member

    Jan 1, 2004
    More Ram Will Be Faster

    But what I am trying for along with others is optimization of performance. So let's say you have two different 1 GB sticks that have the same specs. What I'm asking is there a system diagnostic panel where the performance can be confirmed as either 64bit or 128bit from a pair of ram sticks. Either 2x512's or 2x1GB's. One being apple one being crucial. :)
  20. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    There is a misconception that one RAM design runs "better" than the other.

    There is no "best". The iMac will run the RAM at PC3200 speed whatever RAM is installed as long as it is iMac compatible. You do not get any extra speed out of a particular memory brand, because it's the motherboard that controls all of the memory access timings.

    Apple says that lower latency doesn't matter. I am inclined to agree until shown otherwise - performance optimization from lowered latency has to be built into the motherboard, and there is no evidence I have seen of that.

    So: If you put a 1 Gb iMac compatible RAM beside an existing 512 Mb iMac compatible RAM, it will run at the full iMac G5 64-bit access speed, which is the full design speed of the iMac. It will NOT be slower than it was before.

    If you put a matched pair of RAM into the iMac, it will utilize 128 bit access. This shows approximately 20% improvement in memory access with synthetic memory benchmarks, but according to Barefeats.com, no real-world improvement when averaging across a number of application tests.

    Any speed increases would be attributable mostly to the extra RAM, and not to whether it was 128 bit. It MAY say in the Apple System Profiler whether it is 128 bit or not, I haven't had time to search the archives but it was discussed with vigor about 6 - 8 months ago.
  21. Platform macrumors 68030


    Dec 30, 2004
    Ok Thanks.......well then it can't be too bad to do that :rolleyes: :D

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