ATM — Notes

Functional

• Card insert + PIN.
• Withdraw, deposit, balance, transfer, mini-statement.
• Receipt print.

Non-functional

• 99.9%+ uptime.
• Reversal handling: if cash not dispensed, reverse the debit.

Patterns

• State, Command (transactions), Strategy (denomination split).

Trade-offs

• Online vs offline mode: some ATMs allow limited offline with delayed posting.
• Cash inventory management with denomination optimization is its own LLD.

Refs

• Common LLD references; banking integration whitepapers.