800MHz vs. 1066MHz RAM Pricing

Discussion in 'Mac Pro' started by Michael73, Mar 5, 2009.

  1. Michael73 macrumors 65816

    Feb 27, 2007
    OWC is my go-to place for MP RAM - great service and fast as all get out but what's with the pricing now? 16GB (8 x 2GB) modules for my early '08 (800MHz) stands at $374.99 whereas 16GB (8 x 2GB) modules of the 1066MHz stuff is only $289.99. That's like 29% more. What gives?

    BTW, I never thought I'd really need that much RAM but with *only* 4GB I'm getting all sorts of Page Ins and Outs since I installed VMWare and started running WinXP Pro at the same time I've also got CS4 going. Ever since I tweaked Spaces and went from the default of 4 to 9 I've just got tons of apps open and/or running actively in the background.
  2. bozz2006 macrumors 68030


    Aug 24, 2007
    the RAM for your Mac Pro are FB-DIMMs, and the new ones are not. FB-DIMMs are very specialized and because of the heatsinks, they'll cost more. One reason the RAM for the new mac pro is cheaper is because it's a lot more "standard"
  3. Tallest Skil macrumors P6

    Tallest Skil

    Aug 13, 2006
    1 Geostationary Tower Plaza
  4. Michael73 thread starter macrumors 65816

    Feb 27, 2007
    According the OWC, "FB DIMM technology takes advantage of multiple channel access. Apple recommends the use of 4 or more modules to take advantage of this 256-Bit Wide memory architecture."

    So, does this mean that the new MP doesn't have 256-bit addressing? It would seem like this is a distinct advantage provided you put in the DIMMs in like quads.
  5. nanofrog macrumors G4

    May 6, 2008
    DDR2 FB-DIMM's are even different from standard DDR2. It uses a 69 pin serial connection, rather than a wide parallel connection, which is why standard DDR2 couldn't be used.

    In the case of DDR3, it's a different architecture, and also is not compatible with either DDR2 or FB-DIMM. But it can be used in a 3 channel configuration. This combined with it's differences in architecture, actually allow it to achieve a higher throughput than quad channel FB-DIMM. :eek: ;)

    In both cases, the data is only 64bit, and ECC adds up to another 56. The remaining pins aren't data. Voltages, clocks, grounds, addressing... Addressing has to do with the amount of memory (capacity) that can be accessed, not the actual data itself.
  6. Michael73 thread starter macrumors 65816

    Feb 27, 2007
    I thought each module is 64bits wide + 8bits for ECC = 72Bits at least that's what OWC has on their pages.

    I'm not a technical guru and I guess that given the new architecture I could see how 3 DIMMs of like sized RAM of the new 1066 stuff could outperform the 800MHz stuff, but how on earth could 3 DIMMs of like-sized new stuff outperform 4 of the old stuff :confused:
  7. doctor-don macrumors 65816

    Dec 26, 2008
    Georgia USA
    But compare the 32.0GB prices

    OWC has 800MHz mem for $999.99 whereas 1066MHz mem is $4999.99. Each price is for 8 modules @ 4GB each for 32.0GB total RAM. That is a HUGE difference.
  8. nanofrog macrumors G4

    May 6, 2008
    Oops. Sorry about that. :eek:

    I was thinking in terms of DDR3. It uses 12 pins on the DIMM for the Register/PLL IC, and can operate from 28 to 56 bits. (Remaining pins are for wiring to the memory IC's, voltages, grounds,...) Texas Instrument's SN74SSQE32882ZALR is an example.

    The difference is in the increased prefetch buffer & clock. DDR2 had a 4 bit PFB, while DDR3 has an 8 bit PFB. DDR3 operates at 800-1600MHz data rates, so a 400-800MHz I/O clock, while DDR2 has a data rate of 400-1066, and a 200-533MHz I/O clock. Both transmit data on both rise and fall of the clock, so data rate = 2x I/O clock. Higher frequency (I/O clock) + faster PFB (due to 2x bit rate) does provide faster throughput. :)

    Hopefully, this covers the memory side. ;)

    The on die IMC + QPI (Integrated Memory Controller + Quick Path Interconnect) also helps, as it replaces the slower FSB architecture. Moves data to/from the DDR3 to the CPU faster than was possible with FSB.

    Does this help?
  9. Michael73 thread starter macrumors 65816

    Feb 27, 2007
    Yeah, I saw...WHAT'S UP WITH THAT?!!?

    So, just to recap OWC 2GB DIMMs are 29% more expensive for the 800MHz variety over the 1066MHz stuff BUT 400% more for the 1066MHz variety over the 800MHz stuff (at least at 32GB). WHERE'S THE LOGIC IN THAT?!!!?

    Back to the original question, I still don't understand why a couple of fins for heatsinks are cause for the price variation? All I can come up with is that FB-DIMMs are relatively uncommon and therefore don't benefit as much from economies of production scale nor from competition among producers.

    Any thought on whether the price for 800MHz FB-DIMMs has already bottomed out or do you think we'll go lower? Personally, I get 16GB in a heartbeat at $249.99. Heck, if it came down that much I might even spring for 32GB at $499.99.
  10. nanofrog macrumors G4

    May 6, 2008
    You might want to check out Crucial, particularly for the 32GB kit. They're offering it for $1500USD (Registered btw).

    As for FB-DIMM, it was different than standard non ECC DDR2, required an expensive AMB chip, custom heatsinks, and had a small market. So economy of scale didn't really exist in comparison to it's non ECC cousins. :(

    In the case of DDR3, it uses the same DIMM PCB, and memory IC's, (no matter if non ECC, Unbuffered, or Registered), so economy of scale is going to benefit here given the commonality of the parts, (save the Register/PLL IC, which isn't expensive. ~$9.30USD or less ea.). :)

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