I got a new PC , rig:
Intel core 2 quad Q9550
Asus P5Q Deluxe
Sapphire HD4870X2 2GB GDDR5
2X2 Crosair DDR2 1066Mhz
OS: Windows XP Professional SP2 (32bit)
When i check my computer ( Right click on My computer ) it shows me that i have 3GB RAM instead of 4GB
When i open Catalyst Control Center and check my Graphic card , it shows me 1GB instead of 2GB
Why ? as i know about the ram ,it could be the 32bit windows
about the GFX? i know nothing :X , why its show me 1GB only instead of 2GB ? could it be cuz its Dual GFX card in single pci-e slot or windows?
Your OS is 32 bits and will only have access to about 3-3.5GB of memory on the 4 (which isn't that bad given it's XP and not Vista).
As for video memory, I would have to guess like you: 1GB per GPU, check in CCC if you don't see another "tab" or something for the second GPU. Never used Crossfire so I don't know how CCC behaves with it.
In a 32-bit OS the system can only Address 4GB of memory. Your RAM, video card, and any pci card takes up address space. The 4870x2 has 2GB of cloned memory. Each core gets 1GB of memory that is an exact copy of the other 1GB of memory. The gpus can't access the same memory at the same time, so they came up with the 2GB cloned idea. Your video card has 256x2 bit interface(256 per gpu). If you didn't have a video card you would have 3.5GB of ram. If you added another 4870x2 you would have 2.5GB of ram. Hope this answered your question.
Basicly youve fallen for marketing hype. Your 4870x2 is actually a 2x1GB card, not a 2GB card. You actually have 2GB of VRAM, however only 1GB of it can be utilized per GPU, therefore you practically have 1GB.