MacBook with 4Gb Ram question

Discussion in 'MacBook Pro' started by Neoraven, Jul 25, 2007.

  1. Neoraven macrumors member

    Nov 18, 2006
    Anyone know exactly how much is reserved for APIC and PCI Express? i.e if only .5 Gb are reserved, we can still use 3.5GB of Memory making the 4GB sticks worth it. Useful excerpts?

    [​IMG] [​IMG]

  2. Igantius macrumors 65816

    Apr 29, 2007
    The max. RAM a C2D MB can access is 3.3GB - there're a few threads about this already if you're interested - plus, there was a more technical one over at Ars Technica.
  3. minisamus macrumors newbie

    Jul 24, 2007
    I'm going to assume you're dealing with a MacBook Pro SR which can actually accept 2GB SODIMMs.

    This problem stems from a 32bit system. In short, 32bits of addressing space is 4GB, and if you're using memory mapped IO you can only address up to 4GB - IO space. These systems are 64bit however, and I believe 10.4.x is 64 bit 'enough' to address more than 4GB.

    So, it should work. But if you're trying to decide, you might want to find someone who has it working... :rolleyes:
  4. Neoraven thread starter macrumors member

    Nov 18, 2006
    I'm actually on a C2D MB, I knew that only 3.3GB was addressable and I knew that APIC and PCI Express had allocated memory in the higher ends of the 3-4GB range, but I was curious as to just how much and where/what that excess memory does/goes
  5. Igantius macrumors 65816

    Apr 29, 2007
    That's discussed at the Ars Technica thread I mentioned.
  6. CanadaRAM macrumors G5


    Oct 11, 2004
    On the Left Coast - Victoria BC Canada
    No, that's pretty much wrong. It has nothing to do with the OS. OS 10.3 can address 16 Gb in a G5. Nor is the issue the intel CPU. The issue is the hardware memory controller on the intel logic boards' chipsets.

    CoreDuo machines cannot recognize 2 Gb modules

    Core2Duos (including the MacBook C2D that the OP has) can recognize 2 Gb modules. If you install 4 Gb of memory, due to the requirements the chipset has for hardware resource address space under the 4 Gb ceiling, only 3.3 is available for the OS to use (this is the same with Windows laptops that use the same chipsets)

    The SantaRosa chipset (currently only inthe MacBook Pro) allows access to the full 4 Gb.
  7. Neoraven thread starter macrumors member

    Nov 18, 2006
    Thank you, I was just looking for a definite answer on this. I'm going to go ahead and purchase two 2 gig sticks, to utilize the full 3.3gb of usable memory. I'm tired of Parallels + OS X lag

Share This Page