4gb address space limitation for i386

Erik Trulsson ertr1013 at student.uu.se
Thu Aug 30 15:04:01 PDT 2007


On Thu, Aug 30, 2007 at 05:32:09PM -0400, User Bobby wrote:
> I have an IBM xSeries 350 4xPIII with 5.5gb of RAM, and see that only about 
> 3.5gb is being used under the i386 port.  I've been looking through the
> archives to try and figure out what the root of the problem is and I amn't
> quite sure I know which part of the situation is the real problem.
> 
> Is it a limitation of the i386 port?  That is to say, if there were a 
> specific PIII (i686?) port, would this problem be overcome?  Or is it a 
> hardware limitation?

It is a hardware limitation.

>  Is it necessary to use a not-clean method to access 
> the extra address space (is this what PAE is?)

That is exactly what PAE is for.  


>, and there's no clean
> way around it, regardless of the port?

Correct.


> 
> I was looking at building a PAE kernel, but was discouraged by the lack of 
> usb and certain SCSI support, both of which I'd really like to have (in the 
> case of SCSI, need to have).  Is this lack of support because of an 
> inherent difficulty in the hardware, or could it be overcome in a stable 
> way with modification of the device driver code?

All drivers could potentially be made to work correctly together with PAE.
For some of them it would probably require substantial and non-trivial 
modifications to the driver code.


> 
> My basic (and very hypothetical) question - if I had unlimited time and 
> knowledge (I have limited both), what direction would I take to get access 
> to all 5.5gb of RAM on this particular computer?

Use a PAE-enabled kernel.  Fix the drivers you need that do not currently
work correctly with PAE (or persuade/bribe/blackmail/hire somebody else to
fix the drivers.)


-- 
<Insert your favourite quote here.>
Erik Trulsson
ertr1013 at student.uu.se


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