32-bit Client Effective Memory Limits

Discussion in 'Lenovo' started by BinkNR, Aug 24, 2009.

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  1. BinkNR

    BinkNR Knock off all that evil

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    There are often discussions in this forum on 32 versus 64-bit memory usage—and I came across this great blog post from Mark Russinovich (Microsoft Technical Fellow) that nicely explains 32-bit memory limits, albeit a bit technically. Hope this helps clear some of the misconceptions here.

    http://blogs.technet.com/markrussinovich/archive/2008/07/21/3092070.aspx

    Cheers.
     
  2. Renee

    Renee Notebook Virtuoso

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    The only thing that I've been adamant about is that 32-bits equals 4 gigabytes because the other things really when you get down to it, are questions of definition which in turn depends largely on how things are done.

    The VAX is where all of this comes from, did not have video cards for the three decades that I was there. That seems to be a major bone of contention. Of course, the VAX was not primaily constructed for the single user which machines are today. Todays Windows user is centered around their own machine whereas we were were looking at hardware thats was unbelievably more expensive so we had different design centers than exist today. We made time sharing between users feasible. Today, there is more emphasis, still between processes, but it's in support of a single user. If you wish, you can begin tossing gigabytes of memory around and when you do, the current design centers begin to make sense.

    But....32 bits still equals 4 gigabytes of memory (ordinarily).

    Renee
     
  3. antskip

    antskip Notebook Deity

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    Interesting! You might also like to look at another article on the area: http://www.geoffchappell.com/viewer.htm?doc=notes/windows/license/memory.htm

    It was quoted on Slashdot today. http://slashdot.org/
     
  4. Faruk

    Faruk Notebook Evangelist

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    32-bit means that the address bus is 32-bit wide, allowing you to have 2^32 distinct addresses. This usually also implies that the registers are 32-bits wide.

    If you google for the Intel x86 memory map, you'll see that not all of those 2^32 addresses are used for memory. Some of it is reserved for ROM, I/O and other things.

    You most definitely can't have 4GB of RAM in a 32-bit system because some of the addresses HAVE to be reserved for I/O ports.

    And strictly speaking, assuming no I/O ports, 32-bit only equals 4GB if you're addressing 1-byte chunks of memory (which is the case in the Intel architecture). If you were addressing 2-byte chunks of memory, for example, you'd have 8GB. So 32-bit doesn't "automatically" equal 4GB.
    (Edit: I'm only giving that as an example though, all current desktop/notebook systems address memory in 1-byte chunks)
     
  5. eatbuckshot

    eatbuckshot Notebook Consultant

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    lol wow, i happened to just read through that article a few days ago and tried it out. I somehow found out about it searching about why PAE isn't "working" in windows 7 32-bit rc. I came across some chinese forum/thread that quoted geoff chappell, after translating of course, but i just clicked through to that specific article so I could actually understand. I'm glad to say with those hacks, I got windows 7 x86 to detect and let me use all 8gb of my ram. I wanted to use it for a ramdrive that only has x86 drivers(and i also didn't have access to any other os's and didn't want to reinstall just forthis) Surprisingly, it let me allocate more than 6gb, supporting what geoff said about the transparency of PAE, 36-bit to many drivers
     
  6. Faruk

    Faruk Notebook Evangelist

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    Wanna run some before and after benchmarks? I think PAE adds some overhead/complexity.. since after all, you can't address all that memory natively. That extra memory needs to be addressed somehow :)
     
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