Is continuously adjusted nouce mining and other variable header field, such that the entire hash value is less than or equal Block header target, the smaller the target, the greater the difficulty of mining.
To set a block of time 10 minutes, can be avoided as far as possible simultaneously release block, resulting in the longest chain multiple furcation block, finally bifurcated force is dispersed, and the force is concentrated on a malicious node count back up to the malicious node defensive zone 6 block acknowledgment block chains. In fact, 10 minutes is artificial and, in fact, 8 minutes, 5 minutes principle may be. For a payment system too long, so the ether Place a block of time is 15s, it also turned the mining difficulty, to ensure a stable block of time, it's a consensus agreement called ghost.
Mining difficulty settings to be adjusted once every 2016 blocks (each block Ethernet Square is adjusted once), the expected time of about 14 days, then up and down will adjust the difficulty in accordance with the 2016 actual dug out of time in the code.
The system will automatically adjust, if a malicious node is not adjusted intentionally, target 256 is in the range of 2, 32 bytes of storage, so that it has a compression coding nBits 4 bytes stored in the block header, the additional nBits honest node checks the area, if not adjusted, it will not be accepted.
Because this Bitcoin designers more conservative, such as a block of time, the language used, up to 1M bytes of each block are controversial, all the later development of so many virtual currency.