The reward is agreed-upon by everyone in the network but is generally 12.5 bitcoins as well as the fees paid by users sending transactions. To prevent inflation and to keep the system manageable, there can be no more than a fixed total number of 21 million bitcoins (or BTCs) in circulation by the year 2040, so the “puzzle” gets increasingly harder to solve.
Transactions are defined using a Forth-like scripting language.:ch. 5 Transactions consist of one or more inputs and one or more outputs. 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. The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. 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. Any input satoshis not accounted for in the transaction outputs become the transaction fee.
Bitcoin is a peer-to-peer payment network established in 2009 that uses a virtual currency, the bitcoin, to conduct transactions. Unlike currencies issued by nations, Bitcoin is independent of any country or stock exchange and is entirely digital, with no ties to a central bank, company, or organization. It is used as an investment and medium of exchange by all members of its network. Getting bitcoins of your own is thus a matter of becoming a part of the Bitcoin network by setting up a bitcoin account and wallet.
Mining rewards are paid to the miner who discovers a solution to the puzzle first, and the probability that a participant will be the one to discover the solution is equal to the portion of the total mining power on the network. Participants with a small percentage of the mining power stand a very small chance of discovering the next block on their own. For instance, a mining card that one could purchase for a couple thousand dollars would represent less than 0.001% of the network's mining power. With such a small chance at finding the next block, it could be a long time before that miner finds a block, and the difficulty going up makes things even worse. The miner may never recoup their investment. The answer to this problem is mining pools. Mining pools are operated by third parties and coordinate groups of miners. By working together in a pool and sharing the payouts amongst participants, miners can get a steady flow of bitcoin starting the day they activate their miner. Statistics on some of the mining pools can be seen on Blockchain.info.
Earning bitcoin in exchange for goods and services is just as feasible an option as mining or investing in the digital currency. There are businesses that allow people to earn bitcoin in exchange for services, including some freelance job listing sites where people are paid in bitcoin, as well as businesses accumulate bitcoin by accepting it as a payment method.
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 and released as open-source software in 2009. Bitcoins are created as a reward for a process known as mining. They can be exchanged for other currencies, 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.