Number of unspent transaction outputs The blockchain is a public ledger that records bitcoin transactions.
The maintenance of the blockchain is performed by a network of communicating nodes running bitcoin software. Nevertheless, the “trustless” design requires “each and every user to download and verify the history of all transactions ever made, including amount paid, payer, payee and other details.
To achieve independent verification of the chain of ownership each network node stores its own copy of the blockchain. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending without central oversight.
A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.
Bitcoin network Number of bitcoin transactions per month logarithmic scale  Transactions are defined using a Forth -like scripting language. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output.
To prevent double spending, each input must refer to a previous unspent output in the blockchain. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction.
As in a cash transaction, the sum of inputs coins used to pay can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer. Named in homage to bitcoin’s creator, a satoshi is the smallest amount within bitcoin representing 0. Though transaction fees are optional, miners can choose which transactions to process and prioritize those that pay higher fees.
The size of transactions is dependent on the number of inputs used to create the transaction, and the number of outputs. In the blockchain, bitcoins are registered to bitcoin addresses.
Creating a bitcoin address is nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second.