History
The first bitcoin transaction was recorded in May 2009. The system was proposed by white paper and was implemented as open source software released by bitcoin developer Satoshi Nakamoto. The system and its proof of concept were announced in a 2008–2009 research paper titled How to Automate Digital Cash.
The first successful block was found on 18 October 2009 (on the timestamp of 0200 UTC). The block was found by tokerz, a volunteer moderator for the forum, Bitcoin Forum. https://allportalonline.com/ On this day 1 bitcoin was introduced, having a value of 0.00004549 (0.00045 in 2008 dollars). The total amount of bitcoins created at that time was 21 million. The time stamp of the oldest block (the genesis block) is September 25, 2009, and the average time between blocks is 10 minutes.
The first blockchain explorer and search engine was hosted by Satoshi Nakamoto and released in October 2009 for viewing the first few blocks on the bitcoin blockchain. In November 2010, Blockchain.info founded to centralize blockchain data.
In 2013, the first block on the blockchain passed the landmark 2.5 million bitcoin milestone and the network's block interval was set at 10 minutes. In 2013 the average time between blocks was around 2.6 minutes.
Features
Blocks contain a reference to the previous block using the coinbase transaction, which is a special transaction used to introduce the first transaction in a coinbase transaction block. This allows the transaction to be identified when validating transactions. To ensure no two blocks contain the same coinbase transaction, a nonce is specified using the opcode OP_RETURN. From January 2016 onwards, the nonce in the coinbase transaction is taken from a block's coinbase scriptPubKey, rather than being hard-coded.
It is necessary to reveal the transactions and their associated inputs and outputs in order to fully reconstruct the flow of bitcoins between accounts. This process is similar to how banks record and verify transactions. Any attempt to double-spend coins by repeating the spend in a separate transaction is detected when the second transaction is put into a block and not accepted by the network (as all blocks have a fixed amount of space). To protect against double-spending, each transaction in the blockchain is digitally signed using the private key of the sender.
Blockchain nodes verify transactions by first checking that the conditions of the transactions are valid (that the inputs exist and their sums match the outputs, for example) and then checking that