Genesis
Bitcoin is a digital currency that was first proposed in Oct 2008. Curiously, the proposer had a pseudonym Satoshi Nakamoto and started dissociating himself from any of the developments related to the currency from 2010. Nobody knows who he was. The currency came into existence starting with the genesis block created by Satoshi. The operation was started on 3rd January, 2009 by starting a free source project on Source Forge. In the four years since then, the number of units in circulation has reached more than 10.5 million units. This is half the total number (21 million) of units this currency can ever have, and is hard coded into the system as designed. This is designed to be reached by the year 2040. A Bitcoin unit or BTC can be divided into 100 million units in trade operations. These smaller units are known as satoshis.