[BALU] 64 bit systems
thomas at wsinnovations.com
Fri Jun 8 12:07:39 CDT 2007
Well I stand corrected then. So max ram is 2^40/8, and max mmap() is
2^48/8. I gues this explains were win64 gets its mem limit. The same
should then apply to linux.
Jim Vines wrote:
> According to the wiki. The address space is 48bits-physical plus
> virtual(paged?, swap?), but the physical is 40 bits.
> "Current processor models implementing the AMD64 architecture can
> address up to 256 tebibytes of virtual address space (2 to the 48th
> bytes). This limit can be raised in future implementations to 16
> exbibytes (2 to the 64th bytes). This is compared to just 4 gibibytes
> for 32-bit x86. This means that very large files can be operated on by
> mapping the entire file into the process' address space (which is
> generally faster than working with file read/write calls), rather than
> having to map regions of the file into and out of the address space."
> "Current implementations of the AMD64 architecture can address up to 1
> tebibyte of RAM (2 to the 40th bytes); the architecture permits
> extending this to 4 pebibytes (2 to the 52th bytes) in the future
> (limited by the page table entry format). In legacy mode, Physical
> Address Extension (PAE) is supported, as it is on most current 32-bit
> x86 processors, allowing access to a maximum of 64 gibibytes."
> However keep in mind most motherboards have physical limits, number of
> slots and chip sets limits.
> The virtual address space combined with the efficient i/o to and from
> the HD for swap space, means that fast ram based data bases are usable
> into the 256,000 gigabyte range.
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