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Thread: 64-Bit RAM Cap?

  1. #1
    50 Custom PC's in 10 Years! TheGreatSatan's Avatar
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    Default 64-Bit RAM Cap?

    I know that a 32-Bit OS caps at 3GB. What's the most 64-bit can address?
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    Measure once, curse twice nevermind1534's Avatar
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    Default Re: 64-Bit RAM Cap?

    Quote Originally Posted by TheGreatSatan View Post
    I know that a 32-Bit OS caps at 3GB. What's the most 64-bit can address?
    Actually, 32 bit supports 4GB. I think 64-bit supports 128GB, but very few motherboards support that much.
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  3. #3

    Default Re: 64-Bit RAM Cap?

    32bit supports (mathematically) about 3.12GB (Obviously the hardware doesnt come like this) but with 4bit address extension in windows it can theoretically support more, however feedback is that this method generally doesn't work and is slow, as the PC will have to process these extra 4 bits in a seperate cycle.

    As 64bit systems contain 32 more bits, the total addressable memory is HUGE.
    However Windows XP is capped, as nevermind1534 has stated, to 128GB. I cannot find reference to Vista limits, but would again agree with nevermind1534 that few boards exist that even support 128GB RAM.

    I read an article recently on this subject which I think I found through this website, it may have been through the 'Whats the most Ram you've ever had in a PC' thread that was somewhere else in the forum, but I can't find the page now.

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    Measure once, curse twice nevermind1534's Avatar
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    Default Re: 64-Bit RAM Cap?

    For vista x64, they have a set RAM limit for each version. Ultimate will take th most, obviously.
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    Quote Originally Posted by progbuddy View Post
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  5. #5
    50 Custom PC's in 10 Years! TheGreatSatan's Avatar
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    Default Re: 64-Bit RAM Cap?

    Quote Originally Posted by dead4life View Post
    I read an article recently on this subject which I think I found through this website, it may have been through the 'Whats the most Ram you've ever had in a PC' thread that was somewhere else in the forum, but I can't find the page now.
    http://www.thebestcasescenario.com/f...ad.php?t=16518
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    ...What? progbuddy's Avatar
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    Default Re: 64-Bit RAM Cap?

    64-bit can support up to terabytes of RAM. That's why operating systems are moving towards this architecture, although you can get a 32-bit OS to act as a 36-bit (posted earlier down in the OS thread, I think) and support 128 GB of memory.
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    Religiously tolerant. Luke122's Avatar
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    Default Re: 64-Bit RAM Cap?

    Quote Originally Posted by dead4life View Post
    32bit supports.....
    Welcome to TBCS! Thanks for the input on this subject; memory addressing limits is a subject that comes up again and again here.

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    Fox Furry crenn's Avatar
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    Default Re: 64-Bit RAM Cap?

    32 bit addressing supports 4294967296 bytes of ram.
    36 bit addressing supports 68719476736 bytes of ram.
    64 bit addressing supports 18446744073709551616 bytes of ram.

    For those who dislike maths:
    32-4GB
    36-64GB
    64-18014398509481984KB-17592186044416MB-17179869184GB-16777216TB-16384PB-16EB

    Enjoy.
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    Resident EE mtekk's Avatar
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    Default Re: 64-Bit RAM Cap?

    However, note that no current x86 processor can address the full 64bit memory range. I'm not talking about motherboard limitations or OS limitations, these are actual design limitations of the CPUs. For newer intel, and older AMD64 products they are using 40bit addressing (1TiB max memory), new AMD64 products use 48bit addressing (256TiB). The first intel x86-64 processors only used 36bit addressing, so they can only support 64GiB of memory. See http://en.wikipedia.org/wiki/Amd64

  10. #10

    Default Re: 64-Bit RAM Cap?

    http://msdn.microsoft.com/en-us/library/aa366778.aspx

    Everything you want to know about Windows address space and memory limits.

    CB

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