Non-functional Requirements of the ATM system :-
*Error Message:- Error message should be displayed at least 6 sec. If there is no response from the computer after a request within minutes the card is rejected with an error message.
*Money Dispenses:- The ATM dispenses money if and only if the withdrawal from the account is processed and accepted by the bank.
Each bank may be processing transactions from several ATMs at the same time.
With my best of the knowledge The Error Message which i can selected as the non functional requirements because Error Message is not a particular function of a ATM system. This is a facility provided and necessary for the ATMs. Money dispenses is directly related to your bank account system. This infrastructure of banking system has money dispense non functional requirement i.e. the ATM dispenses money only if the bank accepts the user ATM request , also authenticated by the bank etc.