[ubuntu-uk] 64 bit lucid install

[Tony Travis]

On 27/04/10 12:34, Paul Sutton wrote:
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> Thomas Ibbotson wrote:
>>[...]
>> I'm running 64-bit Lucid with 4GB of RAM, however Lucid is only seeing
>> 3.1GB. It may be I have to set something in BIOS I haven't had time to
>> look into it fully yet, but be aware that it might not just see your
>> 6GB straight off.
>>
>> Tom
>>
> Would some of the missing memory be video memory perhaps which is
> shared, from the main memory.

Hello, Paul and Thomas.

It's not the memory that's shared, it's the address space: You need to 
set the BIOS to enable memory mapping around the 4GiB 'hole' for exactly 
the reason that Paul said. The 1GB of physical memory above 3GiB is 
remapped above 4GiB leaving a 'hole' where peripherals can be memory-mapped.

It's not possible for a 32-bit process to address beyond 4GiB, but PAE 
(Physical Address Extension) enables a 32-bit kernel to access memory 
above 4GiB. Using a 64-bit Linux all 64-bit processes and the kernel 
itself can address > 4GiB. However, 'legacy' processes using the ia32 
libraries would still be limited to ~3GiB.

HTH,

   Tony.
-- 
Dr. A.J.Travis, University of Aberdeen, Rowett Institute of Nutrition
and Health, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, Scotland, UK
tel +44(0)1224 712751, fax +44(0)1224 716687, http://www.rowett.ac.uk
mailto:a.travis at abdn.ac.uk, http://bioinformatics.rri.sari.ac.uk/~ajt