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How Is 64bit Implimented?

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#1 american.swan


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Posted 04 April 2008 - 09:44 PM

How is Vista 32 different from Vista 64 on the processor?

This is a hard question for me to answer. I have tried to find the answer but I only find vague descriptions that don't help.

I have some processor that supports 64bit OS. (I don't know if intel and amd are different)
I install 32bit Vista or XP pro. Now, is part of the processor going to be idle because my os and bios don't use it. Or is the bios going to help out and make it look like I have 2 32bit registers to use...aka two processors....I just don't know.

Is a 64 bit processor one 64 bit string of registers or is it two separate 32bit registers? Will XP pro see only one 32 bit register and therefore have 32bits idle?


Can someone please example this?

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#2 dc3


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Posted 04 April 2008 - 10:54 PM

Wikipedia actually has a pretty good explanation of the difference between 32 bit and 64 bit operation. You can read it here.

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#3 american.swan

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Posted 04 April 2008 - 11:54 PM

Wikipedia actually has a pretty good explanation of the difference between 32 bit and 64 bit operation. You can read it here.

I had been looking at some wiki pages but not that particular one. Thanks for the link.

That article has the following paragraph.

"Currently, most commercial software is built as 32-bit code, not 64-bit code, so it can't take advantage of the larger 64-bit address space or wider 64-bit registers and data paths on 64-bit processors, or, on x86 processors, the additional registers in 64-bit mode. However, users of free or open source operating systems have been able to use exclusive 64-bit computing environments for years. Not all such applications require a large address space or manipulate 64-bit data items, so they wouldn't benefit from the larger address space or wider registers and data paths; the main benefit to 64-bit versions of applications that wouldn't benefit from them would be that x86 versions would be able to use more registers."

So...to answer my question...this paragraph suggest that XP32 would then use 32 bits of the 64 bit register and the other registers would not be used. XP32 wouldn't use the full 64bit address space either, but again it probably wouldn't want to in most cases anyways.

This article gave me the impression that Vista 64 using all 64 bits of the register would also use 64 bits of the address space, but that while running limited or 32 bit data using the full address space would be a "waste". This article mentions z/os which I had never heard of which uses 32bit address space along side 64bit registers.

Have I read the article correctly?

#4 usasma


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Posted 05 April 2008 - 10:13 AM

The program may only use a part of the registers - but the operating system will manage the load according to it's capabilities (and the capabilities of the processor).

The actual usage depends on how the code was written for the processor - and how it was implemented in the Operating System. Add in the ability of 32 bit processors to "emulate" 64 bit processing and it's way too complicated for me to tell.
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