The global state of Ethereum is comprised of accounts that interact with one another through a message-passing framework. The most basic interaction is that of sending some value - like etmp tokens, ether - the native cryptocurrency of Ethereum blockchain. Each account is identified by a 20 byte hex identifier which is called an address - this is generated from public key of the account. There exist two types of accounts:
- Externally Owned Account - An account controlled by a private key, and if you own the private key associated with the account you have the ability to send tokens and messages from it.
- Contract Owned Account - An account that has an associated smart contract code with it and its private key is not owned by anyone
These can be differentiated as follows:
Externally Owned Accounts
- can send transactions (ether transfer or trigger contract code)
- is controlled by private keys
- has no associated code
Contract Owned Accounts
- has associated code
- code execution is triggered by transactions or messages (calls) received from other contracts
- when executed - perform operations of arbitrary complexity (Turing completeness) - manipulate its own persistent storage, i.e., can have its own permanent state - can call other contracts.