Non-ECC RAM for 2008 (3,1) Mac Pro, Voltage Issues

Discussion in 'Mac Pro' started by Policar, Jan 17, 2010.

  1. Policar macrumors 6502a

    Joined:
    Nov 21, 2004
    #1
    I want to upgrade my mac pro from 4gb (4X1gb) to 12gb or 16gb of memory. I know this seems excessive especially since I use the 32bit kernel and 32bit XP, but that's my problem.

    I don't need and can't afford more ECC RAM... So I'm putting mine on eBay and picking up 12gb (to start) of "normal" PC6400 DIMMs. I'd like to know if these would work:

    http://www.newegg.com/Product/Produ...27248&cm_re=pc6400_4gb-_-20-227-248-_-Product

    I see that there are 1.8V and 2.1V DIMMs. Do I want one and not the other? Are there known issues with non-ECC unbuffered memory in mac pros beyond the occasional error?
     
  2. BillB50 macrumors member

    Joined:
    Dec 7, 2009
    Location:
    Bucks County, Pennsylvania
    #2
    Can you tell us why you wish to go to 12 GB? Both OSs you quoted in your post can only address 4GB, since both are 32 bit OS. Secondly, I don't know if non-ecc would even boot. Others more seasoned would know...
     
  3. Policar thread starter macrumors 6502a

    Joined:
    Nov 21, 2004
    #3
    Mac Pros work fine with non-ECC memory, you just can't mix it with ECC. I don't know much about voltage, though, and I think Apple uses 1.8V DIMMs and most of the ones I see online are 2.1V.

    I may be mistaken, but I believe each application can access 4gb so it's not worthless to have more than that on a 32bit system. I believe After Effects, which I use frequently, can (mistake me if I'm wrong) devote 3gb to each core when doing multicore rendering by invoking multiple processes, which is helpful to me since most of my After Effects renders use in excess of 2gb of memory, currently limiting me to one core and slow renders.
     
  4. bozz2006 macrumors 68030

    bozz2006

    Joined:
    Aug 24, 2007
    Location:
    Minnesota
    #4
    OSX can address more than 4GB so it's totally plausible that more RAM would help speed things up, but I would discourage you from going the non-ECC route. non-ECC memory causes kernel panics in Mac Pros and RAM without the huge heatsink gets way too hot. so instead of selling off your old RAM, why don't you keep it and add to it? if you buy from somewhere like macsales.com, you can add 8GB for $300. Then you will have a machine that works properly. You say you can't afford ECC memory, but I want to know if you can afford RAM that doesn't work consistently with your machine.
     
  5. Guiyon macrumors 6502a

    Joined:
    Mar 19, 2008
    Location:
    North Shore, MA
    #5
    If you actually have a 2008 Mac Pro you can't use any of that memory. The 2008 Mac Pro requires matched pairs of 800MHz DDR2 ECC FB-DIMMs which means you cannot use most off-the-shelf DDR DIMMs. I would suggest looking at TransIntl or OWC (this is where I get my RAM).
     
  6. Policar thread starter macrumors 6502a

    Joined:
    Nov 21, 2004
    #6
    The Mac Pro manual (I "actually" have one, yes) states that you can use non-ECC DIMMs so long as they are not mixed with ECC memory. I don't think there's a much more authoritative source than that. transintl.com does have good prices, though, less than twice the price of non-ECC DIMMs.

    To be honest, I don't see why ECC makes a big difference unless you're running a server or a render farm, and I'm just doing compositing work for 1080p video and the occasional 3D render. I figure if you get the voltage and timings right, errors will be minimal. After all, no other mac requires error checking memory. Still, I already get occasional kernel panics and would not welcome any more.

    Anyhow, thanks for the help. I'm going to wait to hear from those who've tried non-ECC DIMMs before deciding what to buy, though, but ECC sounds more tempting than it did before.
     
  7. J the Ninja macrumors 68000

    Joined:
    Jul 14, 2008
    #7
    They meant non-ECC FB-DIMM

    That is not what you linked, what you linked is vanilla DDR2. I'm not even sure that physically fits. Your machine will most certainly not boot with that in it, you may even fry something depending on how the pins are different. That is assuming it even fits in the first place. FB-DIMM may be keyed differently. As for non-ECC FB-DIMM does anyone even sell that? FB-DIMM DDR2 is required by the chipset, which is in turn required for running dual CPUs. End of story.
     
  8. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #8
    FB = Fully Buffered, which is ECC.

    The non ECC version is just 800MHz DDR-2. As it doesn't run hot, it won't need the heatsinks either, and will actually work according to the manual. The PCB notch (keying) is the same for any DDR2 variant.
     
  9. BillB50 macrumors member

    Joined:
    Dec 7, 2009
    Location:
    Bucks County, Pennsylvania
    #9
    I don't mean to take this thread in a wrong direction, but, Bozz2006 stated that OSX can address more than 4 GB of RAM. If the poster stated he's using the 32 bit kernel, is more than 4 GB possible? Does the 32 bit kernel use PAE or some other scheme to get above the 4 GB limit? Obviously the 64 bit kernel doesn't have this limitation.

    Again, apologies for taking this off topic, but I am curious about this point. It's applicable to this poster's question I guess...
     
  10. Guiyon macrumors 6502a

    Joined:
    Mar 19, 2008
    Location:
    North Shore, MA
    #10
    No, the two are not interchangeable as their architecture is completely different. FB-DIMMs use a serial (as opposed to parallel) architecture with the AMB protocol to transmit data to the memory controller using an onboard microcontroller. You can't simply plug a standard DDR2 chip in there, the memory controller has no idea how to address it. Also, per the spec, the notches on the chips are NOT the same.
     
  11. fiatlux macrumors regular

    Joined:
    Dec 5, 2007
    #11
    Non and no.

    Fully Buffered DIMM use an Advanced Memory Buffer (AMB) between the memory controller and the memory module. Unlike the parallel bus architecture of traditional DRAMs, an FB-DIMM has a serial interface between the memory controller and the AMB (source: Wikipedia).

    ECC is something else. ECC DIMMs are those that have extra data bits which can be used by the system memory controller to detect and correct errors (Wikipedia again).

    Most machines will accepte ECC and non-ECC DIMMs (but not a mix). The Mac Pro requires FB-DIMMs.

    Since the AMBs dissipate a lot of heat, FB-DIMMs require heat spreaders.

    The FB-DIMMs designed for the Mac Pro have larger heat spreaders, because the air flow in the memory cage is lower, and the air there has already passed through the CPU coolers and is warmer. My 2nd hand Mac Pro came with regular server FB DIMMs without large spreaders and I have had no problem but YMMV: in a regular server (such as the XServe), the memory modules are typically in a much stronger (and noisier) air flow.

    To make a long story short, you need FB-DIMMs, preferably with large heat spreaders. You wouldn't gain much by going for non-ECC ones if you could find any.

    If you really want to save money, you can try server FB-DIMMs (with regular heat spreaders) and/or purchase on eBay (don't hesitate making direct offers under the buy-it-now prices).

    I went from 4 GB to 12 GB by buying 4x2GB modules (with large spreader) on eBay, for 230 USD total. Not too bad IMO.
     
  12. bozz2006 macrumors 68030

    bozz2006

    Joined:
    Aug 24, 2007
    Location:
    Minnesota
    #12
    Yes, OSX uses PAE to break the 4GB ceiling. If you're interested in the long answer to your question, read this article describing the process. It's interesting.
     
  13. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #13
    There is a lot of confusion and tangents in this thread. The only type of memory that works with Mac Pros from 2006 through 2008 (models: 1,1; 2,1; 3,1) are DDR2 FB-DIMMs, you can't use regular DDR2 modules. FB-DIMMs feature ECC as part of the specification. You won't find them without it.
     
  14. nanofrog macrumors G4

    Joined:
    May 6, 2008
    #14
    I know. It was too early, and I had a massive brain fart. :eek:

    Next time I'll remember: COFFEE FIRST. ;) :p

    This is what ran through my mind, as it does hold true in the '09 models (IMC will run both non ECC and ECC in two flavors <UDIMM and RDIMM, but even these two cannot be mixed>).
     
  15. Policar thread starter macrumors 6502a

    Joined:
    Nov 21, 2004
    #15
    Okay, looks like I'm going with ECC. Thanks for all the info.

    Any advantage (if I have 4X1gb installed already) between 2X4gb and 4X2gb?
     
  16. Umbongo macrumors 601

    Umbongo

    Joined:
    Sep 14, 2006
    Location:
    England
    #16
    4x2GB would mean all 8 memory slots are full and you can balance the memory on each riser (2GB DIMMS in slots 1&2 on each board, 2x1GB in 3&4). You would reach optimal performance. However the 2x4GB gives you room for expansion and the performance difference might not make any real world difference for you.
     
  17. rtrt, Jan 18, 2010
    Last edited: Aug 13, 2011

Share This Page