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Since we are in the Newbies section (and I am still pretty much noob), can you explain to me why this would fail for LTC?
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I would presume because the Scrypt algorithm method used by LTC mining is more dependant on using Random Access Memory in conjuntion with the GPU processor(s).
Depending on what you have your thread concurrency set to, mining will use less or more ram. In the case of cards with less vram, the optimal thread concurrency values typically end up being in a range that it suitable for the amount of vram the card has. My 6950s use 500mb and they are the 1gb versions. Mine at 450khps each.