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On 32-bit x86 systems, the total virtual address space has a theoretical maximum of 4 GB. By default, Windows allocates half this address space (the lower half of the 4-GB virtual address space, from x00000000 through x7FFFFFFF) to processes for their unique private storage and uses the other half (the upper half, addresses x80000000 through xFFFFFFFF) for its own protected operating system memory utilization.

64-bit Windows provides a much larger address space for processes: 7152 GB on IA-64 systems and 8192 GB on x64 systems.

I have several questions about the above quote :

  1. Why low address space is allocated for processes?
  2. "...uses the other half (the upper half, addresses x80000000 through xFFFFFFFF) for its own protected operating system memory utilization." - Why operating system doesn`t use physical addresses for system address space,but uses virtual addresses?
  3. Why on x64 system 8192GB is used for process and for system?In oppose to 32bit OS not all space of addresses is used?

Thank you

YAKOVM
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  • possible duplicate of [Difference between physical addressing and virtual addressing concept](http://stackoverflow.com/questions/3243610/difference-between-physical-addressing-and-virtual-addressing-concept) – Oliver Charlesworth Jul 01 '12 at 19:40
  • @OliCharlesworth - it is not.The post you are talking about gives overview of virtual vs. physical memory.But doesn`t provide the answer for the questions I have asked here – YAKOVM Jul 01 '12 at 19:46
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    You have asked three distinct questions here; in general, you should ask one question per SO post. The question I linked to answers one of your questions. (If it *doesn't* answer your question, you need to edit your question to make it clearer!) – Oliver Charlesworth Jul 01 '12 at 19:47
  • which question does it answer?Please point me - I couldn`t find the answer for any of the questions I asked.In addition all of the questions are related and I asked them together as a "principles" of virtual memory – YAKOVM Jul 01 '12 at 19:55
  • "Why operating system doesn't use physical addresses...". Perhaps I am misunderstanding what it is that you are asking? – Oliver Charlesworth Jul 01 '12 at 19:56
  • @OliCharlesworth - I have rephrased it. – YAKOVM Jul 01 '12 at 20:02

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