Compared to Bitcoin
Many people will come to Ethereum with some prior experience of cryptocurrencies, specifically Bitcoin. Ethereum shares many common elements with other open blockchains: a peer-to-peer network connecting participants, a Byzantine fault–tolerant consensus algorithm for synchronization of state updates (a proof-of-work blockchain), the use of cryptographic primitives such as digital signatures and hashes, and a digital currency (ether).
Yet in many ways, both the purpose and construction of Ethereum are strikingly different from those of the open blockchains that preceded it, including Bitcoin.
Ethereum’s purpose is not primarily to be a digital currency payment network. While the digital currency ether is both integral to and necessary for the operation of Ethereum, ether is intended as a utility currency to pay for use of the Ethereum platform as the world computer.
Unlike Bitcoin, which has a very limited scripting language, Ethereum is designed to be a general-purpose programmable blockchain that runs a virtual machine capable of executing code of arbitrary and unbounded complexity. Where Bitcoin’s Script language is, intentionally, constrained to simple true/false evaluation of spending conditions, Ethereum’s language is Turing complete, meaning that Ethereum can straightforwardly function as a general-purpose computer.