user56566: I'm reading https://en.bitcoin.it/wiki/Difficulty
And I don't get why max target is not (2^256 - 1) which is 0xFFFFFFFFFFFF... but 0x00000000FFFF...?

user208: If the maximum target was 2256-1, every candidate block would be a valid block.
As even the CPU miner in Bitcoin's first software release was capable of doing 100 kH/s or more, this would have led to a very rough start of the chain, with 1000s of blocks produced per second until the difficulty adjusted.
Because of that reason, the maximum target was probably set to a level that would guarantee not too frequent blocks after genesis.

56566: <p>I'm reading <a href="https://en.bitcoin.it/wiki/Difficulty" rel="nofollow noreferrer">https://en.bitcoin.it/wiki/Difficulty</a></p>

<p>And I don't get why max target is not <code>(2^256 - 1)</code> which is <code>0xFFFFFFFFFFFF...</code> but <code>0x00000000FFFF...</code>?</p>
 208: <p>If the maximum target was 2<sup>256</sup>-1, every candidate block would be a valid block.</p>

<p>As even the CPU miner in Bitcoin's first software release was capable of doing 100 kH/s or more, this would have led to a very rough start of the chain, with 1000s of blocks produced per second until the difficulty adjusted.</p>

<p>Because of that reason, the maximum target was probably set to a level that would guarantee not too frequent blocks after genesis.</p>
