text: with an add on card atm system wat would happen if both the persons withdraw money from diff places simultaneo i've an account for which i and my father hold atm cards. now i'm at delhi n my dad at pune and the balnce in the account is rs.10000. both of us r trying to withdraw money from the account at 9:00 in the morning exactly. another problem is i'm tryin to withdraw rs.8000 and my dad an amount of rs.5000 which exceeds the balance of rs.10000. so, wat would happen in such a situation and how could we technically term it??? no,the people who design banking systems have thought of that one...  when you use an atm, you are not directly accessing your bank account, you are simply placing a request for a transaction.  transaction requests are placed in a queue and only one will be processed at a time, for a particular account.  even though both requests are placed at the same time, they will be assigned different transaction numbers, and one will be picked for processing first... usually the one that gets to the queue first.  access to the account would be locked for a short period until the first transaction is completed, so the second transaction would be held in queue.   once the first transaction is completed, the lock will be released and the second transaction will be processed -  in this case, unsuccessfully.  technically, this is called "conflict avoidance"