Nodes and subnet blockchains
Internet Computer subnet blockchains provide physical hardware and resources—like CPU and memory—for performing software operations. Each subnet is a blockchain that consists of some number of individual machines—connected peer computers called nodes—that run the software components of the Internet Computer protocol.
The Internet Computer software components that run on each node are called a replica because they replicate state and computation across all of the nodes in a subnet blockchain.
The core components of a replica are organized into the following logical layers:
A peer-to-peer (P2P) networking layer that collects and advertises messages from users, from other nodes in its subnet blockchain, and from other sub-networks. Messages received by the peer-to-peer layer are replicated to all of the nodes in the subnet to ensure the security, reliability, and resiliency of the platform.
A consensus layer that selects and sequences messages received from users and from different subnets to create input blocks that can be notarized and finalized before being delivered to the message routing layer.
A message routing layer that routes user- and system-generated messages between subnets, manages the input and output queues for applications, and schedules messages for execution.
An execution environment that calculates the deterministic computation involved in executing a program and processes the messages it receives from the message routing layer.
The following diagram provides a simplified overview of the Internet Computer protocol components deployed as a local replica in a development environment.
As a developer, it isn’t necessary to know the details about how your applications and user interactions with your applications are routed through the Internet Computer architecture or replicated on the network. However, a general understanding of the key components can be useful because the development environment includes the replica components to provide a local test network for deployment and a realistic sense of the workflow for a production deployment.