You may have heard that blockchains are composed of peer to peer nodes which are simply devices that participate in the blockchain network. There are different types of nodes performing different functions. These nodes can be divided into two types, full nodes and light nodes. However, these nodes can each be sub-categorized depending on specialty.
Full nodes can be divided into two: let's start with full archival nodes. As their name suggests, they maintain a complete copy of a blockchains' transaction history. Starting from the Genesis block to the most recent one. They are responsible for enforcing the consensus algorithm rules, participating and validating transactions. Incase of an error or failure, the entire blockchain can be reconstructed so long as there exists a single archival node in the network.
Archival nodes can be further sub-divided into four types. Mining nodes, Staking nodes, Authority and master nodes. Mining nodes participate in the process of creating a new block in a proof of work blockchain like Bitcoin. They receive rewards in the form of newly created crypto.
Closely related are Staking nodes which participate in the process of validating new blocks in a proof of stake blockchain. They are often referred to as Validators or validator nodes. They have their crypto locked up which dis-incentivises dishonest & malicious actors. This has the effect of strengthening the network security using purely financial incentives.
The other type of archival nodes are known as Authority nodes. Their use is common in partially decentralised networks. Validators who run these nodes are typically hand-picked by the entity behind the network. Although they perform similar tasks to full nodes, they have the power to veto some specified transactions or suspicious ones. They are commonplace in young centralized blockchains which want to boost the overall network security when a 51% attack is easy to execute as the network is still young.
The last type is Master nodes. Unlike the previous ones, this type can't add blocks to the network, rather, they validate and keep record of transactions. They are more like a utility type of node.
Aside from archival nodes, we have another type of full node known as pruned full node. Just like its name implies, it is a trimmed down version of a full node. Pruned nodes start by downloading the entire blockchain and verify that it is correct. They then discard some of the data and store only an n number of blocks up to a specified period in history. It could also be up to a specified size limit, reducing the amount of disk space required to store the blockchains and run a node. Whereas the technique or parameters for composing a pruned full node may vary, they all have one thing in common, they are basically a full node but do not store the entire blockchain data! They perform the same processes as other full nodes.
Moving on from full nodes, we have light nodes. They typically do not require powerful hardware or high bandwidth to run, enabling access to the blockchain via devices like laptops and smartphones. They are used in day to day operations like checking balances, broadcasting transactions but don't enforce network consensus rules and only store data relevant to transactions being performed fully relying on full nodes to provide them with any other necessary information. A common practical use case is by block explorers like Etherscan on Ethereum.
Lastly, unless you literally live under a rock you've already heard of Bitcoins' lightning network. It is powered by a type of node known as lightning nodes which allow off-chain transactions to reduce the overall load on the main-chain. However, it is important to note that not all nodes are found on all blockchains or follow this particular categorisation, there are often blends of 2 types of nodes or more to perform more varied and advanced tasks.
