Mac Pro 2008 - RAM - max transfer rate?

Discussion in 'Mac Pro' started by sparkie7, Sep 1, 2011.

  1. sparkie7, Sep 1, 2011
    Last edited: Sep 1, 2011

    sparkie7 macrumors 68000

    sparkie7

    Joined:
    Oct 17, 2008
    #1
    Does anyone know the maximum transfer rate of internal RAM?

    Wikipedia states:

    Notably, due to its FB-DIMM architecture, installing more RAM in the Mac Pro will improve its memory bandwidth, but may also increase its memory latency.[19] With a simple install of a single FB-DIMM the peak bandwidth is 8 GB/s, but this can increase to 16 GB/s by installing two FB-DIMMs, one on each of the two buses, which is the default configuration from Apple.

    So this equivalent to a maximum of 800MB/s - 1,600MB/s transfer?
     
  2. sparkie7 thread starter macrumors 68000

    sparkie7

    Joined:
    Oct 17, 2008
    #2
    Barefeats testing http://www.barefeats.com/harper3.html yields up to 7.5GB/s

    so is that the same as 7,500MB/s ?

    SATA II SSD's are 3GB/s, so am I right in interpreting that RAM is twice as fast?
     
  3. sparkie7 thread starter macrumors 68000

    sparkie7

    Joined:
    Oct 17, 2008
    #3
    I tried Xbench (see below)

    Is accurate is this test. Your thoughts on the results?
     

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  4. accessoriesguy macrumors 6502a

    Joined:
    Jul 8, 2011
    #4
    I only know that 2 RAM sticks are faster then 1 due to dual channel. RAM (as of now) smokes SSD's to the ground, idk what the max rate is however.
     
  5. JavaTheHut macrumors 6502

    JavaTheHut

    Joined:
    Aug 15, 2010
    #5
    Are you trying to decide whether to invest in more RAM or use a SSD as a scratch?

    I believe the RAM is a better performer in the long run I think your config would be using PC2-6400 DDR2-SDRAM (dual channel 128-bit) 102.4 Gbit/s 12.8 GB/s 800 MHz DDR2-800?

    List_of_device_bandwidths
     
  6. toxic macrumors 68000

    Joined:
    Nov 9, 2008
    #6
    SATA II has a max bandwidth of 3 Gb/s (6 Gb/s for SATA III), RAM max bandwidth is in excess of 5 GB/s. GB and Gb are not the same thing. the slowest RAM is at least 10 times faster than the fastest SSD.

    however, RAM does not spend much time running at max bandwidth, at least not today. this is obvious since dual/triple-channel yields less than 5% performance gain, even though the max bandwidth is double or tripled.

    relating SSDs to RAM is a pointless exercise unless you plan on making a RAMdisk. they aren't used for the same operations.
     

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