Create ethereum.md

blockchains/ethereum.md

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+## Ethereum notes
+
+
+### Basics
+
+* a state is made up of objects called "accounts", with each account hacing a 20-byte address and state transitions being direct transfers of value and information between accounts.
+
+* an Ethereum account contains four fields:
+   * the nounce: a coutner used to make sure each transaction can only be processed once
+   * the account's current ether balance
+   * the account's contract code
+   * the account's storage
+
+* there are two type of accounts: externally owned accounts (controlled by private keys) and contract accounts (controlled by their contract code)
+
+* a transaction refers to the signed data package that stores a message to be sent from an externally owned account. It contains:
+  * the recipient of the message
+  * a signature identifying the sender
+  * the amount of ether to transfer from the sender to the recipient
+  * an optional data field
+  * STARTGAS, representing the maxium numner of computation steps the transaction is allowed to take
+  * GASPRICE, representing the fee the sender pays per computation step 
+
+* contracts can send "messages" to other contracts, which are virtual objects that are never serialized and exist only in the Ethereum execution environment. It contains:
+  * the sender of the message (implicit)
+  * the recipient of the message
+  * the amount of ether tot transfer alongside the message
+  * an optional data field
+  * STARTGAS
+
+* a message is like a transaction, except it is produced by a contract and not an external actor. A message is produced when a cotnract currently executing code executes the CALL opcode.