[wplug] 4GB Ram not seen by Linux kernel

[Mackenzie Morgan]

On Feb 7, 2008 12:04 AM, Tom Rhodes <trhodes at freebsd.org> wrote:

> On Wed, 6 Feb 2008 23:36:19 -0500
> "Mackenzie Morgan" <macoafi at gmail.com> wrote:
>
> > You're running a 32bit kernel, then?  You could theoretically address
> all
> > 4GB (and not a bit more) on 32bits, except that'd assume you had no
> drivers
> > or firmware or anything.  It varies by hardware just how much you'll see
> on
> > a 32bit OS.  Install 64bit, and you'll be good because that can
> > address....umm....Wikipedia says 16 exbibytes (1 exbibyte = 1024
> pebibytes,
> > 1 pebibyte = 1024 tebibytes, 1 tebibyte = 1024 gibibytes).
>
> Yea, it's 32-bit.  From what I can tell, PAE (physical address
> extentions) exist in the kernel file (perhaps I could rebuild and
> try) and should, theoretically, give me access to the larger
> amount of RAM.  I was also thinking that the OS needs upgraded
> to the 64-bit version; however, I need to double check and make
> sure that the CPU will actually run it.  I doubt a 64-bit
> version will run on a 32-bit CPU, but I've been told (may not
> be correct) that a 64-bit CPU will run either or.  On that,
> as I've not tested either, I reserve the right to be wrong.
>
> Maybe it's likely that even though PAE seems enabled in the
> source (seen with make menuconfig), it's not enabled in the
> default kernel - a rebuild, as noted above, may just fix this
> entire issue.
>

Ah, some hardware doesn't support PAE.  That's down to your CPU, I think.  I
got a kernel panic on boot when I installed Ubuntu 7.10 Server on a laptop
because the kernel is built for PAE.  It said "CPU too old for this
kernel."  If your hardware doesn't support PAE, nothing can be done about
that, AFAIK.

No, a 64bit OS will not run on 32bit hardware.  It is true that 64bit
hardware can do either, though.  That's just a matter of using only half the
registers.  You can't magically double the number of available registers
though.

-- 
Mackenzie Morgan
Linux User #432169
ACM Member #3445683
http://ubuntulinuxtipstricks.blogspot.com <-my blog of Ubuntu stuff
apt-get moo
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