4GB memory

[Lennart Sorensen]

On Wed, Apr 02, 2008 at 10:42:13AM -0400, D. Hugh Redelmeier wrote:
> In the XP days, the swap file was unmoveable.  You could turn off
> static swap file allocation and then defrag & shrink, then turn it on
> again.  I don't know if this applies in the MS Vista era.
> 
> I had to buy MS Vista recovery disks.  I could not boot Vista for
> the first time (after owning the machine for ~5 months).  Acer's one
> year warranty did not apply to Vista -- that was only 90 days (grrr).
> It turns out that under some conditions Vista won't boot if you fiddle
> with the MBR, which, of course, installing Linux does.  I haven't got
> the measure of this problem.  Perhaps it is only the first boot that
> won't work.
> 
> According to Wikipedia's article on PAE
>   http://en.wikipedia.org/wiki/Physical_Address_Extension
> MS Vista SP1 can use PAE to get at all the memory.  So install SP1.
> 
> SP1 was not offered by Windows Update until I deleted the
> hungry-to-install-itself trial version of Norton
> Anti-something-or-other.  Others find some drivers prevent SP1 from
> being offered.  If you care, google.
> 
> That is surprising.  If you use dmesg you should see early on what the
> kernel thinks the physical memory blocks are.  Here's from my machine:
> BIOS-provided physical RAM map:
>  BIOS-e820: 0000000000000000 - 000000000009fc00 (usable)
>  BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved)
>  BIOS-e820: 00000000000e7000 - 0000000000100000 (reserved)
>  BIOS-e820: 0000000000100000 - 000000003ffc0000 (usable)
>  BIOS-e820: 000000003ffc0000 - 000000003ffd0000 (ACPI data)
>  BIOS-e820: 000000003ffd0000 - 0000000040000000 (ACPI NVS)
>  BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
>  BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
>  BIOS-e820: 00000000ff7c0000 - 0000000100000000 (reserved)
> 
> I use x86-64 on my machines that can handle it.  This hardly ever
> causes problems these days, at least in the Red Hat / Fedora / CentOS
> world.  I admit that the advantages on a desktop are minor; sane
> large-memory handling is one of them.

That clearly shows that the BIOS is NOT mapping the extra ram above 4GB
so PAE and the like won't help.  The BIOS has to first do the right
thing before any OS can use the remaining ram.  Some intel chipsets are
incapable of remapping so there is nothing that can be done in that
case.

-- 
Len Sorensen
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