[BALU] 64 bit systems

Thomas Stover 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."
> http://en.wikipedia.org/wiki/X86-64
> 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.
> Jim

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