Asus motherboard? -- never again!

[D. Hugh Redelmeier]

| From: Matthew Godycki <mcg2-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org>

| > My only complain about asus is that their bios demands
| > certain amount of 
| > ramm of the physical side, and last time I upgraded to 4 GB
| > and darn 
| > thing took 850Mb out of it, what's with that.
| > 
| 
| Sounds to me like an OS issue.  32-bit operating systems are routinely only able to address just over 3GB.

Agreed.

There is 4G of address space on the 32-bit PCI bus.  Some addresses
are reserved for I/O devices.  So you cannot fit 4G of RAM in that
address space.

The BIOS typically maps a chunk of 4G of RAM to above the 4G address
space.  This RAM is tricky for an OS to deal with: on many machines,
you cannot do DMA to it.

Because of this, some BIOSes have an option of how this is mapped.  In
fact, they are willing to throw the memory-that-won't-fit away.  I
think that the option might be called "linear" (I forget since I've
never had such a BIOS).

Summary: use an OS willing to handle more than 4G of RAM (64-bit
version or PAE version).  Perhaps you need to adjust a BIOS setting.
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