Why MacBook Pro Core 2 Duo units are limited to 3 GB RAM

“We previously reported that while the MacBook Pro Core 2 Duo can physically accomodate two 2 GB RAM modules for a total of 4 GB, Apple’s specs list the model as able to recognize a maximum of 3 GB of RAM. Today we have some some additional information regarding why the units can only recognize 3 GB, and the questionable nature of other manufacturers’ claims that their Core 2 Duo-based uportables can address up to 4 GB of RAM,” MacFixIt reports.

“The MacBook Pro Core 2 Duo presumably uses Intel’s 945PM chipset, which can physically handle 4 GB of DDR2 RAM. However, a number of items that must be stored in physical RAM space, and when RAM reaches 4 GB, there is some overlap. In other words, in a 3 GB RAM configuration, there is no overlap with the memory ranges required for certain system functions,” MacFixIt reports.

Full article here.

31 Comments

  1. The next Intel Chipset (Santa Rosa is the code name) is supposed to fix the 4GB memory issue. That should be out 1H 2007 according to Intel.

    Also, as for FBDIMMS. Apple has no choice but to use those with the new Xeon Processors. The 5100 series processor requires FBDIMMS. Apple would have to release a desktop with a (Conroe) Core 2 Duo Processor to avoid use of FBDIMMS. But the Conroe processor can not be used in a multi processor configuration.

    my 2 cents

  2. @MacMental.

    Don’t be a dumbass. I’m currently using a G4 ibook 1GHZ proc with 768MB of ram. I can open and use several apps including photoshop, acrobat and quark at once and not witness any slow down what so ever. My mother uses a G3 ibook and still doesn’t know how to use it, bless her, so she’s always got about 10 apps running at once and that still runs about as fast as mine. To say OSX is a memory hog is a lie and telling everyone they need at least 3 gigs of RAM is just snobbery.

  3. I don’t understand this – which shouldn’t be a surprise; this is pretty esoteric board level design stuff, BUT:

    Why would a chipset decide to use memory addresses between 3 gig and 4 gig? Where would the chipset expect to find that memory if it’s not installed? Does the chipset have some onboard memory addressed there? If so, has the idiot at Intel who decided that a chip set – used with a 64 bit processor – should usurp the OS’s memory space been hung, drawn, and quartered? Slowly?

    Just askin’.

  4. Those that think 512MB – 768MB of memory is enough have never used a Mac with 2-4GB of memory. The difference is night and day. Those of you with less then 1GB of memory, join us and learn what a Mac should feel like. It’s only going to get worse from here as well, those of you used to the 512MB – 1GB… your running the bare minimum now. Times change, programs are using more memory, 1GB is barebones scraping now.

  5. M.T.MacPhee asked:
    “Why would a chipset decide to use memory addresses between 3 gig and 4 gig? Where would the chipset expect to find that memory if it’s not installed? Does the chipset have some onboard memory addressed there? If so, has the idiot at Intel who decided that a chip set – used with a 64 bit processor – should usurp the OS’s memory space been hung, drawn, and quartered? Slowly?”

    It’s because the processor is 32-bit. The largest memory address it can use is limited to 2^32 which is 4GB. That address space must be shared by the firmware, video memory and regular memory and so not all of it is available for the regular memory. This is very old news – it’s been a limitation since 32-bit address spaces were conceived. If you want more RAM, get a 64-bit laptop – models using AMD’s 64-bit processor line have been out for many months, just not from Apple. Fully supported by Linux.

  6. AlienApple opined:
    “Those that think 512MB – 768MB of memory is enough have never used a Mac with 2-4GB of memory. The difference is night and day. Those of you with less then 1GB of memory, join us and learn what a Mac should feel like. It’s only going to get worse from here as well, those of you used to the 512MB – 1GB… your running the bare minimum now. Times change, programs are using more memory, 1GB is barebones scraping now.”

    However, before parting with your hard-earned cash, take a few minutes to listen carefully to hear whether you hear hard disk activity when moving between applications or when manipulating large images, etc, in programs. If you do, then you would benefit from more memory as MacOS is having to use your slow hard disk as virtual memory. If not, then increasing your memory will have no effect whatsoever, as your existing memory is already able to fully handle your computing needs. Adding memory only makes computers faster if they are having to frequently swap and page to disk. Otherwise, it’s irrelevant.

  7. DanDrum (since you asked for it) you’re a cretin. You’re even insulting your own mother. She’s doing it the right way.

    I have more than 20 years of experience with Macs and 15 with NeXT computers and I let open all the apps I need without quitting them.
    It’s the way it’s designed for.

    You’re a stupid OS7 user, used to mono-tasking, who still believes apps need to be quitted.

    You’re a cretin!

  8. Mac Matt,

    “It’s because the processor is 32-bit.”

    No, the processor — other than the Yonah chip on the Mac Mini — is 64 bit, but the current Macs use an Intel MB chip set that is limited to 32 bit addressing. If you want full 64 bit goodness, you will have to wait for the Intel Santa Rosa MB chip set. That should also solve the nasty 3G limit on usable address space.

  9. Nice try, Reality Check, but, of course, anyone that knows even a scintilla knows that we *are* talking about 64 bit processors. The Intel Core 2 Duo. Mac users, of course, are used to thinking about 64 bit processors since we have enjoyed them since G5 days. Years and years.

    Now, if you want to be useful, explain why the Intel chipset corrupts the 3-4 gB address space.

  10. Guys, this has zilch to do with the chipset. Take an OS design course!

    32-bit Intel chips can address more than 32 bits of RAM with PAE, which is supported by Linux and Windows. It took a while to develop PAE support in both systems, so it may be a few versions of MacOS before it’s supported there. That’s why Apple is limiting specs to 3GB whereas other manufacturers will sell you 4.

    PAE is an unappealing segmentation of your VM, so Apple may prefer to skip it and move to 64-bit processors instead.

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