where's my memory?

Mikkel L. Ellertson mikkel at infinity-ltd.com
Tue Jul 14 14:19:17 UTC 2009

Neal Becker wrote:
> I have a argument with another user about memory.  He claims that on running 
> linux on his 4G Dell machine, top only reports 3.something memory, he says 
> the missing space is for pci bus.  I think this is only because he's running 
> 32 bit and that 64 bit would give all the memory.
> I tried on my 64bit 8G machine, and it reports
> 8114688k total
> 8114688 * 1024 = 8309440512 (assuming top 'k' is 1024)
> 2**33 = 8589934592
> The diff is:
>  280494080
> I know some will be kernel space, but that doesn't account for 280M.
Check your BIOS settings. I can not remember exactly what it says,
and it varries by BIOS, but there is a setting that controls how it
handles the memory overlap with the PCI memory map. It can remap the
memory or just not use it. Some OSs have a problem with remapping it.

Also, I believe your friend with the 32 bit OS can probably recover
the rest of the memory by running the PAE version of the kernel.

One other thing to keep in mind is that the laptop may be using some
of the system memory for video memory.


  Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!

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