The first cryptocurrency to capture the public imagination was Bitcoin, which was launched in 2009 by an individual or group known under the pseudonym, Satoshi Nakamoto. As of October 2018, there were over 17.33 million bitcoins in circulation with a total market value of around $115 billion (although the market price of bitcoin can fluctuate quite a bit). Bitcoin's success has spawned a number of competing cryptocurrencies, known as "altcoins" such as Litecoin, Namecoin and Peercoin, as well as Ethereum, EOS, and Cardano. Today, there are literally thousands of cryptocurrencies in existence, with an aggregate market value of over $200 billion (Bitcoin currently represents more than 50% of the total value).

The supply of bitcoins grows by the process called “mining” bitcoins. The supply is expected to increase by 10% in 2014 after going up 11.11% last year. The rate of block creation is 6 per hour with each block worth 25 bitcoins (around 25k USD). If more mining power goes online and the block generation increases to 7 blocks per hour for example, the so called “mining difficulty” will go up until the 6 blocks per hour average is reaffirmed. On the other hand if miners generate less coins then the difficulty will go down making it easier to generate new coins. You can read more about the supply of bitcoins here.
Transactions are verified by network nodes through cryptography and recorded in a public distributed ledger called a blockchain. Bitcoin was invented by an unknown person or group of people using the name Satoshi Nakamoto[9] and released as open-source software in 2009.[10] Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies,[11] products, and services. Research produced by the University of Cambridge estimates that in 2017, there were 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.[12]
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