MBPSR 2GB on 2 Chips??? WHY?

Discussion in 'MacBook Pro' started by puuukeey, Jun 11, 2007.

  1. puuukeey macrumors 6502

    Dec 24, 2004
    tristate area
    so the guy at the store whispered in my ear and said to can the ram upgrade. So I get my macbook home and system profiler says that there are two 1 GB cards in there... that means I have to buy 4 gb instead of 2???

    its been so long since I've upgraded ram..
    is this right?
  2. Fearless Leader macrumors 68020

    Mar 21, 2006
    You have 2 1gb sticks correct? If so leave it alone, you don't need more.
  3. noway macrumors regular


    Jun 11, 2007
    Right now, if I understand right, you have 2x 1gig RAM. Total of 2gig.
    If you want a total of 4gig, you need to change those 1gig to 2gig. Then you'll have 2x 2gig (total of gig)

    lol yeah good point. dont throw money out the window. 2gig is more than most laptops on the market...
  4. vagarach macrumors member

    May 14, 2007
    If you want to upgrade to 4GB (which will be much cheaper than what apple will charge) you will indeed have to buy two 2GB sticks of ram and replace *both* 1GB sticks currently installed in your mbp. Alternately, you could just replace one and have 3GB, and not have to waste both sticks (unless you have another laptop which can use them).
  5. Episteme macrumors regular

    Jan 25, 2007
    Apple ships the new MBP with 2x1GB for a couple of likely reason. One is it's cheaper. The other is, it performs better, since with two DIMMs you can take advantage of the RAM running in dual channel mode.

    There was no gain to be had by running in dual channel mode on older MBPs, as the memory and FSB ran at the same speed. With the newer (Santa Rosa Platform) MBP, the FSB runs faster than the memory, so it can take advantage of the higher throughput afforded by dual channel mode.

    If you want to upgrade to 4GB, you'll have to buy 2x2GB DIMMs.
  6. mags631 Guest

    Mar 6, 2007
    Yes, you have to replace both for 4GB -- which cost me like $247 incl tax and shipping for a kit of 2x2GB. What's the problem?
  7. puuukeey thread starter macrumors 6502

    Dec 24, 2004
    tristate area
  8. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    Nooo... Don't confuse clock speed with bandwidth. Dual channel mode is independent of the FSB buss speed or the memory buss speed. In Dual Channel mode, two modules are accessible at the same time, doubling bandwidth to 128 bits, while still operating at the same clock speed (667 MHz). Theoretically, double the number of bits can be transferred in the same number of clock ticks (1/667,000,000th of a second).

    "The dual channel configuration alleviates the problem by doubling the amount of available memory bandwidth. Instead of a single memory channel, a second parallel channel is added. With two channels working simultaneously, the bottleneck is reduced."

    Kingston article (PDF)

    The fact that the FSB is 800 MHz makes no difference, as the memory controller is still limited to 667 MHz. In addition, since RAM has latency, (DDR-2 RAM only responds once every 5 ticks of the clock) it never comes close to saturating the available bandwidth of the memory buss.

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