How does Ethereum change shared state?

Separate execution rules from consensus.

Ethereum supports smart-contract programs executed by nodes. Transactions can call those programs and change state; consensus helps establish the accepted history.

In a teaching registry contract, execution checks whether a caller may edit an entry. Consensus concerns the history participants accept. Calling both simply a smart contract obscures the distinction.

Contract here means a program. Deployment alone does not establish legal enforceability outside the chain.

Begin with the account

An account records an address’s ETH balance and transaction sequence. A wallet prepares a signed request; a contract may apply additional permission rules. Start with accounts and authorization, then follow gas, consensus and finality before moving to Layer 2.

Sources and further reading

Go deeper

Ethereum gas: why failed calls still cost: Separate execution work, transaction value and fees.
Ethereum rollups: which confirmation matters?: Distinguish an L2 response from settlement and withdrawal.

Ethereum and ArcBlock

Ethereum can hold asset records and execute contracts while an application uses ArcBlock services. Applications and assets explains this division and the documented ArcBridge connection. For Ethereum scaling, continue with Layer 2 and Base.

Check your understanding

Are program execution and agreement on history the same task?

No. Execution and consensus have different responsibilities.

Continue along a learning path

Referenced here

Terms

Ethereum
The chain that made programs, not just transfers, the thing a ledger records. Smart contracts as most people mean them come from here, and so does much of the tooling other chains reuse.