One of the most important factors of decentralized networks are the so-called nodes or network nodes. To ensure decentralization, it is necessary to distribute the network across many of these nodes. However, there is not just one type of node, but different types, each of which performs different functions in the network. Basically, every computer that is connected to the (Bitcoin) network can be called a node. In this article, we will list the most important types, describe their function and highlight the differences.
The most important nodes are the so-called"full nodes". As the name suggests, full nodes are basically responsible for storing a complete copy of the entire blockchain and continuously validating and synchronizing it. The full nodes are the backbone of the network, so to speak, as they are responsible for enforcing the consensus rules. As complete permanent storage of the entire transaction history requires a large amount of storage space, there are two different ways of dealing with this. In the area of full nodes, a distinction can be made between so-called pruned and archival nodes.
The special feature of a pruned node is that although it starts downloading and verifying/validating blocks from the genesis block , it discards the oldest blocks when a set limit is reached and only retains their header and block height. However, as the entire blockchain must always be downloaded and the transactions are also fully validated, pruned nodes are regarded as full nodes. They can therefore also verify newer transactions and participate in the network consensus.
In contrast to pruned nodes, archival nodes do not discard older blocks, but archive the entire blockchain (hence the name "archival" nodes). They can be divided into two types. Those nodes that are able to append new blocks to the blockchain and those that only validate them.
The main specification of validating nodes can also be seen from their name. They store the entire blockchain and validate it continuously. As a result, they naturally require more hard disk space than pruned nodes, which can be costly for operators in the long term. Validating nodes are a very important factor for the decentralization and security of the network, as they make the complete history available to all participants and new nodes in the network can then check it themselves without having to trust another instance. Validating nodes can be seen as a kind of "service provider" for the network. They provide historical data (e.g. for block explorers) and they transmit new blocks from miners to other nodes, for example. It is therefore extremely important that these archive nodes can be operated by as many entities as possible. This is one of the reasons why the block size of Bitcoin is deliberately kept small. This ensures that the storage space of the blockchain does not grow too quickly and that many people can afford to operate a validating node and the network is not dependent on large and centralized institutions.
The blockchain is updated and secured via a mechanism known as mining. Mining nodes are network nodes that are allowed to add a new block to the end of the blockchain after providing proof of the required work ("proof of work"). It is extremely important for the mining process to know all the necessary parameters for the next block. These also include data from previous blocks, which is why mining nodes must also act as full nodes.
Light nodes are sometimes also referred to as SPV nodes (Simple Payment Verification) and are used by almost every Bitcoin or crypto enthusiast in the form of "light wallets". As wallets rely on current data from the blockchain to process transactions, they usually come with a light node. This type of network node uses hardly any resources, communicates with the blockchain and relies on full nodes to provide them with the necessary information. As they do not store a copy of the chain, they only query the current status, which block is the last valid one and send transactions for processing. Accordingly, light nodes do not enforce any rules in the network and are not part of consensus building.
