Ethereum at initial launch was started with Proof of Work protocol more over the game plan changes as soon as increasing use-cases brought about escalating transaction fees that brought the network under slow motion and decreasing patronage owing to overloading and congestion on the system.
Going by the foregoing, it was inevitable to introduce Ethereum 2.0 in November 2020; a consensus mechanism innovated to operate Proof of Stake Protocol. This network mechanism would see to gradual transition of Ethereum protocol from Proof of Work to Proof of Stake. Consequently, the system developer made the transition into phases of development starting with implementation of Ethereum 2.0 which upon its success would pave way for ETH 2.1 and then ETH 2.1.5 (System combinations involving POW & POS gradual transfer with sharding process). The last phase would probably be perfected at ETH 2.2 version.
These network improvements are aimed at increasing speed, efficiency and scalability of Ethereum ecosystem.
The most used consensus algorithms in Ethereum are Proof of Work (PoW) and Proof of Stake (PoS). PoW was the first consensus algorithm used in Ethereum that was used in cryptocurrencies. PoS is another type of consensus algorithm developed as an alternative to PoW. PoS and PoW are developed for the same reasons but there are a few fundamental differences. In PoW, the validation of blocks happens according to the stake of participants.