PoS

Proof of Stake (PoS) is an algorithm for choosing a validator to build the next block. Per the PoS algorithm, when a validator owns more coins, the validator has a higher chance to be chosen. Compared to PoW, PoS is much more energy efficient and quicker.

A pure PoS will lead to the richest validator being selected frequently, causing a supernode problem, referring to a node validating the majority of the blocks being added to the chain. This obviously will not work. Additional randomness is required to give other validators better chances. Several randomization methods are available:

• Randomized block selection: Uses a formula to look for the lowest hash value in combination with the size of the stake for selecting a validator.
• Coin age-based selection: Coins owned long enough, say 30 days, are eligible to compete for the next block. A validator with older and larger sets of coins have a better chance of being granted the role.
• Delegated PoS: This implementation chooses a limited number of nodes to propose and validate blocks being added to the blockchain.
• Randomized PoS: Each node is selected randomly using a verifiable random beacon for building the new block.

Ethereum is working on replacing PoW with PoS in future releases.