Discovering Cryptocurrencies

I recently found myself in the market for a mid-range graphics card and latched onto a previously-opened (hence discounted) GeForce GTX 750 Ti from Newegg. (I purchase all my computer equipment from them. They hate patent trolls, as do I. Unlike me, they actually do something about them.)

The GTX 750 Ti is based on the new Maxwell architecture and per online reviews actually vastly improves on previous generations in terms of cryptocurrency hashing power and efficiency, traditionally the realm of ATI graphics cards. Why? Besides generally having more ALUs, ATI chips implement the important right-rotate operation in silicon, whereas NVIDIA chips don’t. Right-rotate is used extensively in Bitcoin’s proof-of-work function, SHA-256, and by extension in scrypt and scrypt-N, leveraged by alternative coins such as Litecoin and Vertcoin. That means when an ATI chip goes to right-rotate by 6, it takes one clock-cycle to complete:

01100101100101001101111001110001 rot 6
= 11000101100101100101001101111001

Meanwhile, most NVIDIA chips have to do two shifts and an addition – three clock cycles:

01100101100101001101111001110001 >> 6
= 00000001100101100101001101111001

01100101100101001101111001110001 < < (32-6) = 11000100000000000000000000000000

OR of previous two operations
= 11000101100101100101001101111001

While the GTX 750 Ti probably still doesn’t outperform a similarly-priced ATI card, it at least remedies that right-rotation penalty. I get about 250-260 khash/s out of it when doing scrypt-2048.

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