Re: [SOLVED] Is my processor 32-bit or 64-bit?
Joe Pfeiffer <pfeiffer@cs.nmsu.edu> writes:
> shawn wilson <ag4ve.us@gmail.com> writes:
>
>> On Tue, Aug 28, 2012 at 1:34 AM, Bob Proulx <bob@proulx.com> wrote:
>>> Stephen Powell wrote:
>>>> By the way, there's something I don't understand. A 32-bit processor can
>>>> only access 4G of "real" (extended) memory, right? So why are there
>>>> motherboards available for 32-bit processors that support installing
>>>> more than 4G of RAM? What good is memory that the processor can't address?
>>>
>>> With PAE (physical address extensions) the processor *can* address
>>> more than 4G of ram. A single process is still limited to 32-bits
>>> which usually works out effectively to 3G of ram but the operating
>>> system can make use of more than this. It can be used for filesystem
>>> buffer cache and for multiple 3G programs. A machine with 6G of ram
>>> for example could run two 3G program at the same time and hold them
>>> both in memory without swapping. Or run one 3G program and still have
>>> 3G for the system to use in filesystem buffer cache. With PAE having
>>> more than 4G of memory is quite useful.
>>>
>>> Using PAE does have a small performance impact. It slows things down
>>> by 2%-3% in my use cases. But the increase in ram for buffers usually
>>> more than makes up for the differences.
>>>
>>
>> iirc, pae is only 48 bits too.
>
> "only" meaning 256 terabytes in this case... I'll be very surprised to
> ever see a 32 bit processor that can make effective use of that much
> memory.
Sorry to follow up my own post -- I hit "send" too fast. My response
was given the assumption that PAE gave a 48 bit physical address space;
of course it doesn't. It gives 36 bits -- 64 GB, which isn't nearly so
outlandish.
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