How many SHA256 hashes can a modern computer compute?

Question

I want to know the mathematical time required for cracking hashes based off different sets of characters.

For example, using only 7 letter, US-ASCII alphabetic character

Answer 1

Remember that a GPU can hash 50x - 100x faster than a CPU. Its harder to program, but more efficient. See www.bitcointalk.com for numbers. I know I do 622 million SHA-256's per sec on a Radeon HD5830.