Is there a specific reason why 1D00FFFF is the target bit for the genesis block and not 1CFFFFFF? Both bits are forcing 8 zeros in the front of the hash (hexadecimal).

Regards steff

1 Answer 1


In the custom uint256 encoding used in Bitcoin, bit 0x00800000 denotes the sign, so 0x1CFFFFFF actually denotes the value -2200(223 - 1). Obviously the target value cannot go negative, so this aspect of the encoding is not useful in this context, but for whatever reason, that's what Bitcoin's creator chose.

  • Thank you that was helpful. I am not so deep in coding. That means when I am looking at the last 6 digits 000000 to 7FFFFF are positive and 800000 to FFFFFF are negative?
    – steff123
    Commented Apr 30, 2022 at 20:01
  • 1
    @steff123 That's right. Commented Apr 30, 2022 at 21:44

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