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Comment Re:You use GPUs for video games? (Score 5, Informative) 112

This is the explanation I've been given for the disparity between Nvidia and AMD:
https://en.bitcoin.it/wiki/Why_a_GPU_mines_faster_than_a_CPU#Why_are_AMD_GPUs_faster_than_Nvidia_GPUs.3F

Specifically:

Secondly, another difference favoring Bitcoin mining on AMD GPUs instead of Nvidia's is that the mining algorithm is based on SHA-256, which makes heavy use of the 32-bit integer right rotate operation. This operation can be implemented as a single hardware instruction on AMD GPUs (BIT_ALIGN_INT), but requires three separate hardware instructions to be emulated on Nvidia GPUs (2 shifts + 1 add). This alone gives AMD another 1.7x performance advantage (~1900 instructions instead of ~3250 to execute the SHA-256 compression function).

For GPU programming I've enjoyed Nvidia's CUDA package greatly over wrangling OpenCL that Radeon relies on.

Comment Re:You use GPUs for video games? (Score 5, Interesting) 112

Haha, I'm at less than 1:1 electricity to bitcoin ratio after ~5 months.
Kill-A-Watt says I've used approx $68.23 of electricity at 11.5 cents per kWh. Bitcoins currently trade at 1 to $30 and I've got 2.2 bitcoins. The Radeon 6770 was (and still is) ~$110.

Additional factors to consider:
-The bitcoin machine is also my daily workstation so if it were running headless and otherwise unused it would have probably done better in the electricity used category.
-It makes a damn fine space heater and I've enjoyed it immensely this winter.
-My focus in this project was to learn hands-on about scientific computing applications and it's been great for that.

In conclusion: as a business it would have been a flop, partially because I haven't optimized the setup for that application. As a learning opportunity and 200 watt heater it's been phenomenal.

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