text: 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.\n\nTransaction requests are placed in a queue and only one will be processed at a time, for a particular account.\n\nEven 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.\n\nAccess 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.\n \nOnce the first transaction is completed, the lock will be released and the second transaction will be processed -  in this case, unsuccessfully.\n\nTechnically, this is called "conflict avoidance"