Mailinglist Archive: opensuse (3605 mails)

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Re: [SLE] 32-bit machines hit physical RAM limit at 4GB?
  • From: James Knott <james.knott@xxxxxxxxxx>
  • Date: Sun, 11 Jun 2006 16:06:33 -0400
  • Message-id: <448C77C9.80405@xxxxxxxxxx>
Jerry Feldman wrote:
> On Sun, 11 Jun 2006 12:40:16 -0400
> James Knott <james.knott@xxxxxxxxxx> wrote:
>
>> While I don't have the exact details of PAE, in general memory mapping
>> works by mapping physical memory outside of the normal addressing range,
>> to an address within that range. This means that only a portion of that
>> physical address range can be visible at a given time. An application
>> has to be able to tell the operating system what portion of the physical
>> memory it wants and also where in address space it wants it to be located.
> The way an application works in Linux is that it is layed out into a
> 32-bit or 64-bit virtual environment. In general, an application
> consists of 3 major sections:
> Text - these are the instructions
> Data - Initialized data
> BSS - Unititialized data.
> Everything is mapped into a virtual address space. Additionally, shared
> libraries are also mapped into virtual memory. This virtual memory is
> blocked into pages (the page size can be changed on some systems).
> When a page is resident in physical memory, its virtual addresses are
> translated to physical addresses.

PAE is not virtual memory. Virtual memory is a method of making disk
space appear as memory. PAE is a memory mapping technique, that allows
an applcation to access memory (real or virtual) beyond the normal 4 GB
limit.


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