Is node a single computer ?

In practice, the term “node” in a blockchain network typically refers to a single instance of the blockchain software running on a physical or virtual machine. Here’s how it usually plays out in practice:

1. Physical Computers: Most commonly, each node is a separate physical computer. For instance, in a decentralized blockchain like Bitcoin, thousands of physical computers around the world run Bitcoin Core (the software that implements the Bitcoin node). These computers might be personal desktops, servers, or specialized mining rigs.
2. Virtual Machines: Nodes can also run on virtual machines provided by cloud services like AWS, Google Cloud, or Azure. These virtual nodes operate just like physical nodes but are hosted in a cloud environment. Organizations might use cloud-based nodes for scalability, reliability, or cost reasons.
3. Multiple Instances on One Physical Machine: In some scenarios, especially for development or testing purposes, one physical computer might run multiple instances of node software. This setup can simulate a network with multiple nodes without needing multiple physical machines.
4. Light Nodes on Mobile or IoT Devices: Lightweight or mobile nodes can run on smartphones or IoT devices. These nodes don’t store the entire blockchain but interact with full nodes to perform transactions or retrieve data. They rely on full nodes to get complete blockchain data and to validate transactions.
5. Mining Rigs: In proof-of-work (PoW) blockchains like Bitcoin, mining rigs can be thought of as specialized nodes. These are powerful machines or clusters of machines dedicated to solving cryptographic puzzles to validate transactions and secure the network.
6. Full Nodes: For major blockchains like Bitcoin and Ethereum, many nodes are full nodes. They store the entire blockchain and perform extensive validation of transactions and blocks, ensuring network security and integrity.

In Summary: Practically, a node is usually a single instance of blockchain software running on a single computer or virtual machine. The key aspect is the role it plays in the network, whether it’s storing the complete blockchain (full node), validating transactions, or performing other network functions.