ICP ARCHITECTURE — HOW IT WORKS INTERNALLY

The Internet Computer is composed of four main layers:

LAYER 1 — HARDWARE (Nodes)

Physical machines running the ICP protocol. Each node runs the IC Replica software. Nodes are organized into subnets.

LAYER 2 — SUBNETS

Groups of nodes that run in consensus. Each subnet is an independent blockchain that canister logic runs on. Subnets are interconnected via NNS-coordinated routing.

LAYER 3 — CANISTERS

Smart contracts on ICP. Unlike Ethereum smart contracts, canisters:

- Have their own memory (heap + stable)

- Can hold web frontend code

- Can be upgraded without losing state

- Execute instructions in deterministic time

LAYER 4 — USERS AND CLIENTS

End users interact with canisters through:

- Internet Identity (authentication)

- Candid (interface description language)

- HTTP outcalls (external APIs)

MESSAGE FLOW:

User -> Gateway -> Subnet Router -> Consensus -> Execution -> Canister -> Response

Each layer handles a specific concern. This modular architecture is what enables ICP to scale horizontally by adding new subnets.

Next: Part 3 — Chain-Key Cryptography

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