When a hard fork is scheduled, how does the program recognize the hard fork? And how to make the whole network recognize the new algorithm?

  • Which algorithm specifically?
    – jtgrassie
    Commented Nov 19, 2018 at 18:22
  • Not specific. I want to know how hard fork is recognized by every upgrade.
    – user9076
    Commented Nov 19, 2018 at 18:29
  • Well each fork is hardcoded in the software to happen at a particular block height. Therefore it is recognized as soon as people are running the latest software and the height is reached. Code is modified ahead of time to make use of the fork version. Note that "version" can be misleading as there could be a new block version, transaction version, PoW variant or other that is tied to a hard fork version, not all are changed at a given fork version.
    – jtgrassie
    Commented Nov 19, 2018 at 19:04

1 Answer 1


Every hard fork introduces a new version that is programmed to "handle" the fork. Something like "Up until block height XXX do this, starting from block height XXX+1 do that".

Older versions will not be able to do that, because when they were released, no one knew what will the requirements be for the next hard fork. This is the reason that before every hard fork people are being told over and over to update their version.

Every hard fork relies on the hope that most of the network will upgrade to the new version - something that goes pretty well so far.

  • So who knows to generate a new version?
    – user9076
    Commented Nov 19, 2018 at 18:30
  • Developers, ahead of a fork, decide what features go into that fork and set the fork height in code. Before the fork hits, a new version of the software is released (with the code changes). Users download and run this new version (ideally before the fork height).
    – jtgrassie
    Commented Nov 19, 2018 at 19:09
  • Do you have the code change examples?
    – user9076
    Commented Nov 20, 2018 at 5:30

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