Main Memory Address Range and IGD.

Hello,

I have been reading a few Intel data sheets and keep coming across the following -

"This address range extends from 1 MB to the top of Low Usable physical memory that is

permitted to be accessible by the (G)MCH (as programmed in the TOLUD register). All

accesses to addresses within this range will be forwarded by the (G)MCH to the DRAM

unless it falls into the optional TSEG, or optional ISA Hole, or optional IGD stolen VGA

memory"

The last bit is confusing me about the stolen VGA memory, why would anything written to the stolen VGA memory not be forwarded to DRAM.

Is it because the CPU can't write to this area but the IGD can as it's using it as it's frame buffer?

Any help would be appreciated,

Thanks.