Why 7970 GHz Edition 6GB work like a 7970 classic ?

[davco77]

Hello everybody

i just buy a sapphire video card :
- VAPOR-X HD 7970 GHz Edition 6GB GDDR5
but she work like a 7970 classic at 3GB.
i use hascat lite v0.09
If some one have a idea why ? if i have a specific drive to install or if hashcat is not compatible with this type of card ? ...

thank you.