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What is "difficulty" and how it relates to "target"? states that the largest possible target value (max target value) is:

0x00000000FFFF0000000000000000000000000000000000000000000000000000

The Difficulty page on the Bitcoin wiki also mentions the same value as the highest possible target.

The same is also the target value in genesis block and the first 2016 blocks.

Why is that the largest (max) target value? Is it one of the consensus rules? Thus, the target value can increase/decrease depending on the current hash rate but must be less than a given value?

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  • Searching for 0x00000000FFFF0000000000000000000000000000000000000000000000000000 on this site results in a list of 23 posts. In the future, could you please check whether your question has been asked before?
    – Murch
    Jan 2 at 16:41
  • @Murch My question was focused on why 0x00000000FFFF0000000000000000000000000000000000000000000000000000 is the maximum target value, in terms of whether it is some math that limits the value to be higher or is it just a consensus rule. I have not found anywhere that this is because it is just a consensus rule. All questions are mainly related to how difficulty and target are calculated and what is the relation between them. I see no reason to close the question and downvote.
    – LeaBit
    Jan 2 at 17:12
  • Your question is titled "What is the largest possible target value?", which is answered in both the topics I linked, while the answers also explain that it is so by definition. If your main question is not "what is the largest possible target", but "Why is 0x00000000FFFF0000000000000000000000000000000000000000000000000000 the max target?", please edit your question’s title to reflect that. Happy to reopen in that case.
    – Murch
    Jan 2 at 17:40
  • On second thought, I would then consider it a duplicate of bitcoin.stackexchange.com/q/67727/5406, so I’ve added that as an original.
    – Murch
    Jan 2 at 17:46
  • @Murch Ahh, let it stay as it is (closed). Its fine. I just wanted to know whether its consensus rule.
    – LeaBit
    Jan 2 at 17:49

1 Answer 1

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Is that one of the consensus rules?

Yes.

Thus, the target value can increase/decrease depending on the current hash rate but must be less than a given value?

Yes. In addition, it can only increase or decrease by a maximum factor 4 every retarget period.

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  • it can only increase or decrease by a factor 4 every retarget period To me, this sounds like it can only increase or decrease by 4 times in each retarget period, and that no value in between is allowed (for example, the target cannot be "eased" by 1.3 times). As far as I know, 4 and 1/4 are the upper and lower bounds, but everything in between is allowed. Am I missing something?
    – LeaBit
    Dec 31, 2023 at 5:12
  • 1
    Yes, 1/4 is the lower bound factor, and 4 is the upper bound factor. If either of those limits is exceeded, a factor 1/4 or 4 is used instead. Dec 31, 2023 at 5:18

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