Have a look in this thread:
https://bitcointalksearch.org/topic/hd-radeon-6990-pulling-around-320-mhashs-how-can-i-get-more-44639
Looks like you're having a similar situation.
Topic: Just installed HD6990 but I only see one GPU... advice requested (Read 916 times)
I have been reading the forum for some time and also have been mining for a while. I have one rig with four 6870s and another with two 5830s. I decided to add a 6990 to my machine (personal use machine not a mining rig) but when I installed it I only see one of the GPUs for mining. I am running Win7 with the latest Catalyst drivers (11.6 I think) and using poclbm for mining.
Has anyone run into this before? After searching online for answers I have only seen one post describing the same situation and they claimed that updated drivers fixed their issue. I wouldn't have purchased a 6990 if I was building another rig but bang for buck since I had my existing system with an open PCI-E slot it was a no brainer but right now it is only performing 340MH/s (I haven't overclocked it yet since I need to get the other GPU working first) which isn't much better than my 5830's that overclocked are doing 300-310MH/s and they only cost $109 compared to the 6990 at $700. I am expecting 700-750MH/s once I figure this out.
Any suggestions are much appreciated.
Has anyone run into this before? After searching online for answers I have only seen one post describing the same situation and they claimed that updated drivers fixed their issue. I wouldn't have purchased a 6990 if I was building another rig but bang for buck since I had my existing system with an open PCI-E slot it was a no brainer but right now it is only performing 340MH/s (I haven't overclocked it yet since I need to get the other GPU working first) which isn't much better than my 5830's that overclocked are doing 300-310MH/s and they only cost $109 compared to the 6990 at $700. I am expecting 700-750MH/s once I figure this out.
Any suggestions are much appreciated.
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