This document explains how to set up a private or testnet Ethereum chain using Geth software. It discusses components needed for a custom genesis block, including the genesis block's properties such as mixhash, nonce, gas limit, and difficulty. Additionally, it mentions important Ethereum improvement proposals and the major releases of Ethereum, specifically Frontier and Homestead.

1. Genesis
Introduction
Geth is widely used to interact with Ethereum networks. Ethereum software enables a user to set up a
“private” or “testnet” Ethereum chain. This chain will be totally different from main chain.
Component that tell ​geth​ that we want to use/create a private Ethereum Chain:
1. Custom Genesis file
2. Custom Data Directory
3. Custom Network Id
4. Disable Node Discovery
Genesis
Genesis block is the start block of the blockchain, i.e., ​block 0. ​A block which not points to a predecessor
block.
Coinbase
This is ​meaningless​ in the genesis block, but the goal was to make the genesis block look identical to any
other block on the blockchain, so the value exist.
Mixhash, Nonce
Both used together to determine if the block was mined properly. These are ​meaningless​ in genesis block.
But make them a random value is good, so that other peers don’t accidently connect to your chain by
having the same exact genesis.
Gaslimit
The maximum number of computations any block on that chain can support. (Set it to a high value to avoid
being limited when testing).
Difficulty
It is mining difficulty. It should be set to low so miner can easily mine.
ParentHash
The 256-bit hash of the previous blocks header. This is ​meaningless​ in the genesis block since block 0
has no parent.
Timestamp
Output of Unix time() function, when the block was created.
Alloc
Pre-funded address (40 digits hex string). This will not create an account in genesis.
Config
Blockchain Configuration
eip155Block
Ethereum Improvement Proposal, where developers propose ideas to improve Ethereum.
homesteadBlock
Second major release of Ethereum. First one was ​Frontier.