What is "graphics memory aperture base" in Intel chipsets?

I'm trying to understand how I can paint simple graphics in x86 protected mode on Intel chipsets. I already (kind of) know how to do that with VGA interface, and I'm trying to understand how I could use G35 Express to do the same. For this purpose I'm studying this document.

I can't understand what "graphics memory aperture base" is; is there anything in the PCI configuration space with that name? For instance, at page 164 the document says:

It represents an offset from the graphics memory aperture base and is mapped to physical pages through the global GTT开发者_运维技巧.

I still need to study a lot, I only skimmed through the previous volumes, but I suspect this is an important concept. Also, do you know where I can find a friendly explanation of this architecture, or another Intel one?

EDIT - Some additional findings

I'm having a look to another another Intel document, 317607.pdf, and it looks like what they call "Graphics Memory Range Address" at page 231 is actually the "Graphics Memory Aperture Base Register" of page 58. However it's a PCI configuration register starting at 0x18.

@ SPRQ: thank you, i think it's a similar concept to the AGP aperture but according to page 52 of the same document:

Note: AGP Aperture no longer exists with PCI Express.

It's something else.

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"Graphics Memory Aperture Base" is a reference to AGP memory or system memory mapped for use by the graphics controller for image or command buffers. The GTT is a page-translation table scheme similar to CPU MMU page tables for mapping system physical memory to a linear AGP address space. So in AGP memory space you can deal with a logically continuous address space which is mapped by the chipset and graphics controller to a set of physical memory addresses references from the CPU.

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a good reference http://msdn.microsoft.com/en-us/library/windows/hardware/ff568296(v=vs.85).aspx. This explains what aperture space is used for.