About block 644
Bitcoin block 644 was mined by Unknown on January 16, 2009 at 12:21 AM UTC, 5 min 26 s after block 643. That is faster than the 10-minute average the network aims for: blocks come in bursts because finding one is pure chance.
It confirmed 1 transactions in 0.00 MB (0.0% of the 4 million weight-unit limit). The median transaction paid 0.00 sat/vB, and all fees added up to 0.0000 BTC. With the 50.000 BTC subsidy of halving era 1, Unknown earned 50.0000 BTC for this block.
Block 644 is number 645 of 2,016 in difficulty epoch 0; 1,371 blocks remain until the next difficulty adjustment at block 2,015. The next halving is at block 210,000, 209,356 blocks after this one.
Its hash starts with 8 zeros: that is the proof of work, a number below the target that the whole network’s hashrate had to search for. Unknown found 8 blocks in the week before. Today the block has 971,983 confirmations, so it is settled beyond any practical doubt.