[mabbo]

Two questions:

Mining bitcoins is about being the first one to generate the hash that satisfies having however many 0s. Whoever gets there first wins the prize, cool.

Does that mean that you can only get new bitcoins in blocks of 25? If my mining program gets unlucky, and never gets a hit, do I get nothing for it? Or are there schemes where I am helping, and I get a portion?

Further, is there something in the data being hashed that includes the previous block chain?

Otherwise, couldn't I make myself some free bitcoins by pre-computing the hash for a transaction I'm going to do in the future, and verifying it first? Sure it might take some computing power, but with no competition I just need to make sure that my costs are less than 25 bitcoins- and at today's prices, that's a lot cash to work with.

[krallja]

> If my mining program gets unlucky, and never gets a hit, do I get nothing for it? Or are there schemes where I am helping, and I get a portion?

Correct, if you are mining alone, it is all-or-nothing. One way to distribute this risk is pooled mining, where you join a group of other miners and split the rewards.

[krallja]

> Further, is there something in the data being hashed that includes the previous block chain?

Yes, the block chain structure includes the previous block; otherwise it would just be a block set :)

[haakon]

To be precise, each block contains the hash of its previous block.