The unit of account of the bitcoin system is a bitcoin. Ticker symbols used to represent bitcoin are BTC[a] and XBT.[b][72]:2 Its Unicode character is ₿.[1] Small amounts of bitcoin used as alternative units are millibitcoin (mBTC), and satoshi (sat). Named in homage to bitcoin's creator, a satoshi is the smallest amount within bitcoin representing 0.00000001 bitcoins, one hundred millionth of a bitcoin.[2] A millibitcoin equals 0.001 bitcoins; one thousandth of a bitcoin or 100,000 satoshis.[73]

To be accepted by the rest of the network, a new block must contain a proof-of-work (PoW).[75] The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash.[85][4] The PoW requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target.[7]:ch. 8 This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is the ascending natural numbers: 0, 1, 2, 3, ...[7]:ch. 8) before meeting the difficulty target. 

Several news outlets have asserted that the popularity of bitcoins hinges on the ability to use them to purchase illegal goods.[135][222] Nobel-prize winning economist Joseph Stiglitz says that bitcoin's anonymity encourages money laundering and other crimes, "If you open up a hole like bitcoin, then all the nefarious activity will go through that hole, and no government can allow that." He's also said that if "you regulate it so you couldn't engage in money laundering and all these other [crimes], there will be no demand for Bitcoin. By regulating the abuses, you are going to regulate it out of existence. It exists because of the abuses."[223][224]
EthereumPrice.org was developed by Ether0x in March 2016 to allow users to easily track the price of Ethereum both historically and in real-time. The platform has since evolved to include several fiat currencies (EUR, GBP, JPY and others) as well as price data for a number of Ethereum ERC20 tokens and other blockchain currencies. More recently, prediction data from Augur was also added to provide insight into the future price expectations of the Ether market. Price data is currently sourced from multiple exchanges with the weighted average price of these assets being calculated by CryptoCompare.com. For more details on the weighted average calculation, see our FAQ.
Bitcoin is a digital asset designed to work in peer-to-peer transactions as a currency.[4][135] Bitcoins have three qualities useful in a currency, according to The Economist in January 2015: they are "hard to earn, limited in supply and easy to verify."[136] Per some researchers, as of 2015, bitcoin functions more as a payment system than as a currency.[32]
According to The New York Times, libertarians and anarchists were attracted to the idea. Early bitcoin supporter Roger Ver said: "At first, almost everyone who got involved did so for philosophical reasons. We saw bitcoin as a great idea, as a way to separate money from the state."[126] The Economist describes bitcoin as "a techno-anarchist project to create an online version of cash, a way for people to transact without the possibility of interference from malicious governments or banks".[129]
Ethereum's blockchain uses Merkle trees, for security reasons, to improve scalability, and to optimize transaction hashing.[61] As with any Merkle tree implementation, it allows for storage savings, set membership proofs (called "Merkle proofs"), and light client synchronization. The Ethereum network has at times faced congestion problems, for example, congestion occurred during late 2017 in relation to Cryptokitties.[62]
Network nodes can validate transactions, add them to their copy of the ledger, and then broadcast these ledger additions to other nodes. To achieve independent verification of the chain of ownership each network node stores its own copy of the blockchain.[76] About every 10 minutes, a new group of accepted transactions, called a block, is created, added to the blockchain, and quickly published to all nodes, without requiring central oversight. This allows bitcoin software to determine when a particular bitcoin was spent, which is needed to prevent double-spending. A conventional ledger records the transfers of actual bills or promissory notes that exist apart from it, but the blockchain is the only place that bitcoins can be said to exist in the form of unspent outputs of transactions.[7]:ch. 5
After much debate, the Ethereum community voted and decided to retrieve the stolen funds by executing what’s known as a hard fork or a change in code. The hard fork moved the stolen funds to a new smart contract designed to let the original owners withdraw their tokens. But this is where things get complicated. The implications of this decision are controversial and the topic of intense debate.
The Ethereum Virtual Machine (EVM) is the runtime environment for smart contracts in Ethereum. It is a 256-bit register stack, designed to run the same code exactly as intended. It is the fundamental consensus mechanism for Ethereum. The formal definition of the EVM is specified in the Ethereum Yellow Paper.[34][37] On February 1, 2018, there were 27,500 nodes in the main Ethereum network.[38] Ethereum Virtual Machines have been implemented in C++, Go, Haskell, Java, JavaScript, Python, Ruby, Rust, Elixir, Erlang, and soon, WebAssembly (currently under development).
Mining is a record-keeping service done through the use of computer processing power.[e] Miners keep the blockchain consistent, complete, and unalterable by repeatedly grouping newly broadcast transactions into a block, which is then broadcast to the network and verified by recipient nodes.[75] Each block contains a SHA-256 cryptographic hash of the previous block,[75] thus linking it to the previous block and giving the blockchain its name.[7]:ch. 7[75]

EthereumPrice.org was developed by Ether0x in March 2016 to allow users to easily track the price of Ethereum both historically and in real-time. The platform has since evolved to include several fiat currencies (EUR, GBP, JPY and others) as well as price data for a number of Ethereum ERC20 tokens and other blockchain currencies. More recently, prediction data from Augur was also added to provide insight into the future price expectations of the Ether market. Price data is currently sourced from multiple exchanges with the weighted average price of these assets being calculated by CryptoCompare.com. For more details on the weighted average calculation, see our FAQ.


^ Jump up to: a b c d "Statement of Jennifer Shasky Calvery, Director Financial Crimes Enforcement Network United States Department of the Treasury Before the United States Senate Committee on Banking, Housing, and Urban Affairs Subcommittee on National Security and International Trade and Finance Subcommittee on Economic Policy" (PDF). fincen.gov. Financial Crimes Enforcement Network. 19 November 2013. Archived (PDF) from the original on 9 October 2016. Retrieved 1 June 2014.
Vitalik Buterin picked the name Ethereum after browsing Wikipedia articles about elements and science fiction, when he found the name, noting, "I immediately realized that I liked it better than all of the other alternatives that I had seen; I suppose it was the fact that sounded nice and it had the word 'ether', referring to the hypothetical invisible medium that permeates the universe and allows light to travel."[9]
Ether is a token whose blockchain is generated by the Ethereum platform. Ether can be transferred between accounts and used to compensate participant mining nodes for computations performed.[3] Ethereum provides a decentralized virtual machine, the Ethereum Virtual Machine (EVM), which can execute scripts using an international network of public nodes.[4] The virtual machine's instruction set, in contrast to others like Bitcoin Script, is thought to be Turing-complete. "Gas", an internal transaction pricing mechanism, is used to mitigate spam and allocate resources on the network.[4]
There is ongoing research on how to use formal verification to express and prove non-trivial properties. A Microsoft Research report noted that writing solid smart contracts can be extremely difficult in practice, using The DAO hack to illustrate this problem. The report discussed tools that Microsoft had developed for verifying contracts, and noted that a large-scale analysis of published contracts is likely to uncover widespread vulnerabilities. The report also stated that it is possible to verify the equivalence of a Solidity program and the EVM code.[41]
To be accepted by the rest of the network, a new block must contain a proof-of-work (PoW).[75] The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash.[85][4] The PoW requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target.[7]:ch. 8 This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is the ascending natural numbers: 0, 1, 2, 3, ...[7]:ch. 8) before meeting the difficulty target.
Both blockchains have the same features and are identical in every way up to a certain block where the hard-fork was implemented. This means that everything that happened on Ethereum up until the hard-fork is still valid on the Ethereum Classic Blockchain. From the block where the hard fork or change in code was executed onwards, the two blockchains act individually.
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