As different peers on the network will see transactions at different times, transaction ordering is essential to ensure that there is no instance of bitcoins being recorded as being sent to two different users. This is the role of the Bitcoin blockchain, which acts as a ledger of all valid transactions propagated through the network.

The first block in the Bitcoin blockchain was Block 0 (the Genesis Block) which was hardcoded into the Bitcoin Software. It was produced on 3 January 2009 at 18:15:05 UTC and contains a single coin generation transaction. The script used to input this transaction contains an encoded message which when decoded reads “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks”. The purpose of using this Times headline message was apparently to show that the Genesis Block could not have been created before that date.

The initial block reward was 50 bitcoin, but that halves with every 210,000 blocks. At the time of the Trial it was 6.25 bitcoin. It is presently 3.125 bitcoin. The total number of bitcoin capable of being generated as rewards is capped at 21 million bitcoins in total. Bitcoin is configured to have a new block produced every 10 minutes on average. This means that the target hash needs to change according to the collective computing power of the peers competing in the mining process. The difficulty level itself changes according to the expected time to produce blocks divided by the actual time, meaning that difficulty increases or decreases depending on the collective computation power.