Re: 6GB memory and XP 32 bit

Tech-Archive recommends: Repair Windows Errors & Optimize Windows Performance

On Sun, 04 Oct 2009 12:15:55 -0700, ToddAndMargo
<ToddAndMargo@xxxxxxxxxxx> wrote:

Ken Blake, MVP wrote:
On Sat, 03 Oct 2009 19:29:08 -0700, ToddAndMargo
<ToddAndMargo@xxxxxxxxxxx> wrote:

Hi All,

I have a customer with two Vista 64 bits trying
to run software that explicitly states its does not
work with Vista, especially 64 bit Vista. Oh, what
a mess!

Question: her computers have 6 GB of memory.
If I change her over to XP 32 bit, being
that 32 bit OS's only can use 4 GB of memory,
what happens to the extra 2 GB of memory?
Does it just get ignored or do I get a BSOD?


It gets ignored, but it's not just 2GB that gets ignored; it's more
like 3GB.

Here's the scoop on it:

All 32-bit client versions of Windows (not just Vista/XP/7) have a 4GB
address space (64-bit versions can use much more). That's the
theoretical upper limit beyond which you can not go.

But you can't use the entire 4GB of address space. Even though you
have a 4GB address space, you can only use *around* 3.1GB of RAM.
That's because some of that space is used by hardware and is not
available to the operating system and applications. The amount you can
use varies, depending on what hardware you have installed, but can
range from as little as 2GB to as much as 3.5GB. It's usually around
3.1GB.

Note that the hardware is using the address *space*, not the actual
RAM itself. If you have a greater amount of RAM, the rest of the RAM
goes unused because there is no address space to map it to.

Thank you. Great explanation.


You're welcome. Glad to help.

--
Ken Blake, Microsoft MVP (Windows Desktop Experience) since 2003
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