Sign in with
Sign up | Sign in
Your question

wrong video memory allocation

Last response: in Motherboards
Share
December 14, 2008 5:22:07 PM

hi guys,

i have a question about the memory allocation of my graphics card. my ati radeon 3870 has 512MB memory but the memory allocation in windows only shows 256MB.

the PCI-to-PCI bridge shows 512MB (CFF00000 - EFEFFFFF), but only 256MB (D0000000 - DFFFFFF) is allocated to my grapics card. as far as i can see, the remaining 256MB is not used for other devices.

if anyone can help me, i would really appreciate :) 

00000000 - 0009FFFF : System board
000A0000 - 000BFFFF : ATI Radeon HD 3870
000A0000 - 000BFFFF : PCI bus
000A0000 - 000BFFFF : PCI standard PCI-to-PCI bridge
000C0000 - 000DFFFF : System board
000E0000 - 000FFFFF : System board
00100000 - 7FFFFFFF : System board
80010000 - FFFFFFFF : PCI bus
CFE00000 - CFEFFFFF : PCI standard PCI-to-PCI bridge
CFF00000 - EFEFFFFF : PCI standard PCI-to-PCI bridge
D0000000 - DFFFFFFF : ATI Radeon HD 3870

F0000000 - F3FFFFFF : Motherboard resources
F8000000 - FBFFFFFF : Creative SB X-Fi
FE600000 - FE7FFFFF : Creative SB X-Fi
FE900000 - FE9FFFFF : PCI standard PCI-to-PCI bridge
FE9FC000 - FE9FFFFF : Marvell Yukon 88E8053 PCI-E Gigabit Ethernet Controller #2
FEA00000 - FEAFFFFF : PCI standard PCI-to-PCI bridge
FEAEC000 - FEAEFFFF : Microsoft UAA Bus Driver for High Definition Audio
FEAF0000 - FEAFFFFF : ATI Radeon HD 3870
FEBFF800 - FEBFFBFF : Standard Dual Channel PCI IDE Controller
FEBFFC00 - FEBFFFFF : Standard Enhanced PCI to USB Host Controller
FEC00000 - FEC00FFF : Motherboard resources
FED00000 - FED003FF : High precision event timer
FED13000 - FED19FFF : System board
FED1C000 - FED1FFFF : Motherboard resources
FED20000 - FED3FFFF : Motherboard resources
FED50000 - FED8FFFF : Motherboard resources
FEE00000 - FEE00FFF : Motherboard resources
FFB00000 - FFBFFFFF : Motherboard resources
FFF00000 - FFFFFFFF : Motherboard resources

setup:
- intel c2d e6300
- p5w dh deluxe
- 2gb corsair xms2
- sapphire radeon 3870
- win xp pro 32-bit
December 22, 2008 6:00:58 AM

That is how it should supposed to be. The card is fully able to use all the vram anyways
a b V Motherboard
a b } Memory
December 22, 2008 10:52:40 AM

modfreak333 said:
i have a question about the memory allocation of my graphics card. my ati radeon 3870 has 512MB memory but the memory allocation in windows only shows 256MB. the PCI-to-PCI bridge shows 512MB (CFF00000 - EFEFFFFF), but only 256MB (D0000000 - DFFFFFF) is allocated to my grapics card.

That's because there is no relationship between the address space allocated to your graphics card and the amount of RAM it has. Yes, I know, there are 1000 people who say that the graphics card needs memory address space for graphics RAM. And if there were a million of them, it would still not be any more correct.

Your graphics card needs address space independent of the amount of RAM. It is not entirely correct to say there is no relationship between graphics RAM and address space allocated for the graphics card. There is no direct relationship.

The following is a mile-high overview of what happens...

The device manufacturer decides what resources the device should request from BIOS during PCI configuration. This is programmed through the device firmware and the ASIC or card itself, which must comply with relevant PCI, ACPI (old PNP) BIOS, and other specifications.

The device gets a chunk of address space, some of which is inclusive of the bridge it resides behind. At this point, the system has not addressed the card's RAM (except for a small legacy frame buffer). It has only reserved a chunk of address space for that device based on how much the device requested (and other system resource considerations). The graphics driver then loads, determines how its address space should be used, and declares it to the rest of the system.

Typically, a graphics card with 64MB or less RAM is going to use 1:1 mapping between RAM and its physical address space. A graphics card with 128MB may or may not. A graphics card with 256MB or more definitely will not. Instead, the graphics driver will bank switch to reach all its RAM through an MMIO window or some equivalent scheme.
!