[Wylug-help] Extra RAM not being recognised

[linux at felixu.com]

Hi

I tried to upgrade my desktop's memory from 512M by adding a 1G unit.

The BIOS (I think) picks it up, because when GRUB shows up, it says something 
about 636K lower / 1570688K upper memory.

I've tried switching the RAM units around, and I've also tried appending 
mem=1536M on the end of my kernel line in my grub config, but my system still 
only recognises 1G altogether according to /proc/meminfo or top.

Any ideas where I could turn next?

Many thanks,

Felix.