Re: [Xen-users] 4GB memory installed, 3.5GB shown (Xen 3.2 + PAE)

[Dimitri Puzin <max@xxxxxxxxxx>]

Wouter de Geus schrieb:
> > Hello,
Hi,

> >
> > I have recently upgraded one of my machines, both in hardware and
Xen version.
> > In the old situation it had 3GB of memory and Xen 3.1, worked like a
charm.
> > After upgrading it has 4GB of memory and Xen 3.2.
[...]

Same thing here. I have a tyan S5112 which has 4 GB phys. RAM installed
however  the max. mem. size the system can address is limited to 4GB.
PAE doesn't work. 64 bit systems don't need PAE. They can address all of
the RAM directly.

The PCI address space lies in the system addressable space in the upper
~768 MB, starting somewhere at 3.3 GB. The actual beginning may be a bit
different, depending on the installed components, BIOS/settings, etc. If
PAE (here I mean hardware support for PAE, which includes chipset
function) is available then the physical memory which collides with the
PCI addr range is remapped to another address, normally beginning
somewhere at 4096MB. However if PAE support isn't available, then the
last ~768MB of RAM are hidden. Otherwise it would be impossible to
address any device in the system because of address space collision
between the virtual PCI address range and physical memory address range.

The exact specifics of the chipset and addressable memory are noted in
the manual of your mainboard. As a rule, I don't buy/get any hardware
with max mem size equal to the mem size I intend to install.

Hope this could clear some things for you.


Regards,

Dimitri Puzin aka Tristan-777

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