> My ~700MB came from 'prtconf -v' and looking at the
> difference between physical and reported;
> 
> amup# prtconf | head -2
> System Configuration:  Sun Microsystems  i86pc
> Memory size: 3396 Megabytes
> amup# 

The  "3396 Megabytes" is reported when booted as a xVM / Xen dom0?

How much is reported when you boot without xVM / Xen?

> Doing a little more digging with xm the numbers look
> a lot worse and don't seem to make much sense; sense
> in that prtconf is reporting more memory than xm
> dmesg is reporting as being allocated...
> 
> An extract from 'xm dmesg'
> 
>  xVM version 3.0.4-1-xvm
> Latest ChangeSet: Tue Dec 04 09:56:10 2007 +0000 13231:f6074ad033f3
> 
> (XEN) Command line: /boot/amd64/xen.gz
> (XEN) Physical RAM map:
> (XEN)  0000000000000000 - 00000000000a0000 (usable)
> (XEN)  00000000000f0000 - 0000000000100000 (reserved)
> (XEN)  0000000000100000 - 00000000dfe8cc00 (usable)
> (XEN)  00000000dfe8cc00 - 00000000dfe8ec00 (ACPI NVS)
> (XEN)  00000000dfe8ec00 - 00000000dfe90c00 (ACPI data)
> (XEN)  00000000dfe90c00 - 00000000e4000000 (reserved)
> (XEN)  00000000fec00000 - 00000000fed00400 (reserved)
> (XEN)  00000000fed20000 - 00000000feda0000 (reserved)
> (XEN)  00000000fee00000 - 00000000fef00000 (reserved)
> (XEN)  00000000ffb00000 - 0000000100000000 (reserved)
> (XEN) System RAM: 3582MB (3668144kB)
> 
> Aside from the non-contiguous memory ranges (where
> did they go?)

A part of the 4G address space is reserved for PCI devices.

> I have 0xDFE2CC00 usable memory, or
> 3582MB.  4096 - 3582 = 514MB lost before anything is
> allocated.

Hmm, is there a BIOS setup option to remap the
memory that is lost due to PCI device address space
at an address >= 4GB?  The BIOS should have something
like "Memory Hole Remapping" and it should be enabled
so that the OS can use all of the available physical ram.

Of cause this also depends on the chipset used on the
mainboard, there are chipsets that can't access memory
at addresses >= 4GB.
 
 
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