user12577: Just out of curiosity, I downloaded cpuminer, signed up at a mining pool site and started the miner.  It seems to be doing something.
[2014-01-22 22:51:09] 1 miner threads started, using 'sha256d' algorithm.
[2014-01-22 22:51:09] Starting Stratum on stratum+tcp://stratum.bitcoin.cz:3333 
[2014-01-22 22:51:10] Stratum detected new block
[2014-01-22 22:51:12] thread 0: 2097152 hashes, 1600 khash/s
[2014-01-22 22:51:42] Stratum detected new block
[2014-01-22 22:51:46] thread 0: 56289640 hashes, 1652 khash/s
[2014-01-22 22:52:47] thread 0: 99121136 hashes, 1624 khash/s
[2014-01-22 22:53:48] thread 0: 97418224 hashes, 1599 khash/s
[2014-01-22 22:54:40] thread 0: 95913336 hashes, 1821 khash/s

I was under the impression that mining could not be done without first downloading the whole chain (that takes about 3 days to download).  Is cpuminer really doing something or just showing me some fake data?

user11253: Mining by yourself requires that you have the whole blockchain. However, when you choose to mine as part of a pool, the pool operator maintains the full blockchain and just sends parcels of work out to the miners. (Of course, in this arrangement you have to trust the pool operator.)

12577: <p>Just out of curiosity, I downloaded cpuminer, signed up at a mining pool site and started the miner.  It seems to be doing something.</p>

<pre><code>[2014-01-22 22:51:09] 1 miner threads started, using 'sha256d' algorithm.
[2014-01-22 22:51:09] Starting Stratum on stratum+tcp://stratum.bitcoin.cz:3333 
[2014-01-22 22:51:10] Stratum detected new block
[2014-01-22 22:51:12] thread 0: 2097152 hashes, 1600 khash/s
[2014-01-22 22:51:42] Stratum detected new block
[2014-01-22 22:51:46] thread 0: 56289640 hashes, 1652 khash/s
[2014-01-22 22:52:47] thread 0: 99121136 hashes, 1624 khash/s
[2014-01-22 22:53:48] thread 0: 97418224 hashes, 1599 khash/s
[2014-01-22 22:54:40] thread 0: 95913336 hashes, 1821 khash/s
</code></pre>

<p>I was under the impression that mining could not be done without first downloading the whole chain (that takes about 3 days to download).  Is cpuminer really doing something or just showing me some fake data?</p>
 11253: <p>Mining by yourself requires that you have the whole blockchain. However, when you choose to mine as part of a pool, the pool operator maintains the full blockchain and just sends parcels of work out to the miners. (Of course, in this arrangement you have to trust the pool operator.)</p>
