The definition of the term "nodes" can significantly vary depending on the context of usage. In computer and telecommunication networks, nodes perform various functions and can act as information relay points or end communication points. Typically, a node represents a physical network device, but virtual nodes also exist.
Simply put, a network node is a point through which messages can be created, transmitted, or received. Here we will discuss different types of Bitcoin nodes: full nodes, super nodes, miner nodes, and SPV clients.
Bitcoin Nodes
The blockchain, designed as a distributed system, is a network of computer nodes. This enables the use of Bitcoin as a decentralized peer-to-peer (P2P) digital currency, architecturally resistant to censorship, without the need for intermediaries during exchange from user to user (regardless of how far apart they are).
Blockchain nodes play a crucial role in maintaining connectivity and performing various functions. Any device connected to the Bitcoin interface can be considered a node as they exchange information with each other. These nodes also transmit information about transactions and blocks across a distributed network of computers using the Bitcoin peer-to-peer (P2P) network protocol. However, each computational node is defined according to its specific functions, hence there are various types of Bitcoin nodes.
Full Node
Full nodes are a crucial part of Bitcoin network security as they support its operation and participate in transaction and block verification, thus they may also be referred to as full validating nodes. Full nodes can also relay new transactions and blocks on the blockchain. Typically, a full node downloads a copy of the Bitcoin blockchain, with every block and transaction, but this is not a mandatory requirement for a full node (instead, a pruned blockchain copy may be used).
Many voluntary organizations and users run basic Bitcoin nodes to aid the Bitcoin ecosystem. Currently, there are about 9,700 public nodes operating on the Bitcoin network. Note that this number only includes public nodes which are part of the Bitcoin tracking nodes, visible and accessible (aka. Listening nodes).
Besides public nodes, there are many other hidden nodes that are not visible (non-tracking nodes). These nodes usually operate behind firewalls using hidden protocols such as Tor, or simply because they are configured not to be tracked.
Tracking Nodes (Super Nodes)
In fact, a tracking node or super node is essentially the same as a full node that is publicly accessible. It connects with other nodes and provides access to information upon connection request. Thus, a super node serves as a data transmission point that can be used as a data source and a communication bridge.
To reliably operate a super node, it is necessary to maintain a constant connection with several nodes worldwide and transmit blockchain history and transaction data. Therefore, a super node likely requires more computational power and a better internet connection than a full hidden node. It also needs to operate round the clock and have multiple established connections.
Miner Nodes
To have the ability to mine bitcoins in the current competitive environment, investment in specialized hardware and mining software is required. These mining software programs are not directly related to Bitcoin Core and run in parallel to attempt to mine Bitcoin blocks. Miners can work solo (solo miners) or in groups (pool miners).
While full nodes of solo miners use their own copy of the blockchain, pool miners work together, each contributing their own computational resources (hash power). In a mining pool, to operate a full node that could be called a miner pool full node, only the pool administrator is required.
Lightweight or SPV Clients
Also known as Simplified Payment Verification (SPV), lightweight clients are those that use the Bitcoin network but do not actually act as full nodes. Therefore, SPV clients do not contribute to network security as they do not store a copy of the blockchain and do not participate in the process of transaction verification and confirmation.
In short, SPV is a method by which a user can verify whether certain transactions have been included in a block without needing to download the entire block's data. Thus, SPV clients rely on information provided by other full nodes (super nodes). Lightweight clients act as communication endpoints and are used by many cryptocurrency wallets.
Client vs Mining Node
It is important to note that running a full node is not the same as running a full mining node. While miners have to invest in expensive mining hardware and software, anyone can run a full validating node. Moreover, before attempting to mine a block, a miner must gather pending transactions that have previously been accepted as valid by full nodes. The miner then creates a candidate block (with a group of transactions) and attempts to mine that block. If the miner manages to find the correct solution for this block, they broadcast it to the network, and other full nodes will verify the validity of this block.
Conclusion
Bitcoin nodes interact with each other through the Bitcoin P2P network protocol, thereby ensuring the integrity of the system. A node that misbehaves or attempts to spread incorrect information is quickly identified by honest nodes and disconnected from the network.
Although running a full validating node does not provide financial rewards, it is strongly recommended as it provides trust, security, and privacy for users. Full nodes enforce the rules, protect the blockchain from attacks and fraud (such as double spending). Additionally, a full node does not need to trust others, and it allows the user to have full control over their money.