Blockchain is a public ledger which records all transactions between the nodes in the network. Miners verify new blocks of transactions and add them to the chain of previous blocks. Thus, this continuous chain is referred to as blockchain. However the property of immutability of any blockchain is dependent on the number of confirmations of the block containing the transactions.

Bitcoin confirmations and irreversibility

For a transaction to be completed it is imperative that it be verified and approved by miners. The number of blocks generated after the creation of the said block is called as confirmation. Any block that is being trailed by only one to six blocks is not considered to be completely irreversible. All transactions in a block being trailed by more than six blocks are said to be completely irreversible. It could take anywhere between 10 minutes to over 10 hours for the transaction to be considered completely irreversible. The speed at which transactions can be verified is dependent on the number of pending transactions in the mempool.

What is a block and how is it related to blockchain?

A block is mainly a list of records, which are continuously added to the blockchain. Each block consists of a hash of the previous block, a timestamp and transaction data. As miners create blocks of validated transactions, they are added to the blockchain.

A bitcoin wallet only reflects the current balance in a wallet and the digital currency is always stored on the blockchain. The address, also known as a public key, holds a record of all transactions done on it. Each public key has a private key which is used for transactions. Any transaction performed needs to be signed with a digital signature generated from both the addresses. Once a bitcoin transaction has been published to the network, nodes check if the bitcoin to be sent actually exists or not. After this, the transaction is considered to be validated and is then added to a block, which is then mined into the ledger.

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