The largest 64 bit integer is:
18,446,744,073,709,551,615 or, in hex: 0xffffffffffffffff
but there aren't that many sats, there are only:
00,021,000,000,000,000,000 or, in hex: 0x004a9b6384488000
sats that can ever exist (actually slightly less due to rounding decisions involved in the issuance schedule)
According to a google search the largest bitcoin transaction ever is this one which sent this number of sats:
‎00,000,002,613,938,974,287 or, in hex: 0x000002609ae76e4f
So a lot of bits in the 64 bit output amount field have never actually been used in any mainnet bitcoin transaction
Just to clarify, 18,446,744,073,709,551,615 is the largest unsigned 64-bit integer. Which makes sense in this context, since you aren’t sending negative sats.
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Hm... Satoshi wasted in theory at least one byte then. In practice 2. Anyway. I was thinking in the context that I wish bitcoin was more divisible. And it clearly it was possible for bitcoin to be more divisible if one bitcoin was defined as a bigger integer (and the initial reward was still 50 btc) without actually sacrificing anything.
I feel that it may be possible in the future 1 satoshi to be too big of a value. And as far as I have read this cannot be fixed without some very disruptive hard fork. (And yeah, subsatoshi on the lightning network is not the same as it can't really be settled).
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