How ATMs work | General financial discussion | Discussion forum

Hi everyone,

I have a trivial question about how ATMs work, in particular; how does the ATM work in relationship to updating the withdrawer's account balance?
i.e. When someone withdraws the money, is his/her bank account immediately updated (real-time), or are these transactions being stored in the ATM Controller which then runs a batch process to update the respective bank's accounts?

Take the following scenario:
Say I have $1,000 withdrawal limit but I only have $600 in my current account.
If I withdraw $300 from it, will the ATM update that current account straight away (real-time), or will it log this transaction and run a batch process at a certain point in time to update my current account?
What I would like to know is that, if the later is the case (i.e. a batch process is in place), will the system allow me to withdraw $300 two more times, (hence exceeding my account balance by $300) since I haven't gone over my daily $1,000 limit?

Thanks in advance!