What is replica?

General
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Please forgive my rudimentary question, but what does replica mean? My understanding is that it is in some way “node” or “catchup packeage”, but I can’t be sure. What is it? Thank you in advance.

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Providing context is always helpful. Any particular literature you’re referencing?

Ideally it would refer to the one of the many nodes that are part of a subnet. Each one of the nodes is a replica.

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Thank you for your reply.

I’ve read several blogs, but the definitions of replica and node are vague, so I’m not sure what these terms are, as I don’t know much about technical theory. This blog, for example, talks about replica and node.

Each of the replicas holds all of the states of the canisters and processes, as well as all the messages that should be processed by the canisters.

Additionally, the network might at some point want to add a node to a subnet, perhaps to increase the fault tolerance on the subnets, but this node comes in without knowing anything about the state of the subnet

My understanding is that they are the same, but if they are the same, why don’t they use the same words and why do they use them differently?
I understand that catchup package is not directly related to the difference between the words replica and node. In my opinion, I think the following is true

Replica on ICP protocol layer
Node on physical layer or physical machine

I may be wrong, but I would like to know about this.

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A node is a physical machine running as part of the Internet Computer.

A replica is an instance of Internet Computer software that runs on a node. It implements the Internet Computer Protocol (ICP).

So nodes are hardware, replicas are software.

There’s another slight difference.

Every node belongs to one subnet (not necessarily the same). All of the nodes in a subnet replicate state and computation to achieve consensus. Hence, the term “replica”. So you’ll often hear replicas specifically used in the context of a subnet, whereas nodes can be used more generally, i.e. node providers, tokenomics, etc.

See Nodes and subnet blockchains :: Internet Computer

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Thank you.I understand very well.

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This is correct. Well said.

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