Of course things such as mismatched account balances (i.e. the account balance does not equal all credits - debits) or erroneous postings due to bugs happen in

Of course things such as mismatched account balances (i.e. the account balance does not equal all credits - debits) or erroneous postings due to bugs happen in the banking IT world. It's just that they are not that visible because only the people affected and that are quick enough in checking their balances will learn about it and after a few hours or days, when they notice the mistake, they will just fix the entries. (And if you thought you were clever and transferred all the funny money away, they are going to sue you to get it back; see e.g. this Quora thread for bank errors and legality: https://www.quora.com/If-my-bank-mistakenly-deposits-1-000-000-into-my-account-am-I-legally-allowed-to-spend-it-before-they-realize-their-mistake https://www.quora.com/If-my-bank-mistakenly-deposits-1-000-0...) EDIT: Also, to answer the question: I think distributed computing is hard. The bank will usually have all their account balances on one huge central mainframe in one location, so you do not need to rely on computers talking to each other. And also, a bank does not really need to publish credits and debits at the same time - they just have to make sure your account is debited at or before the other account is credited (in fact, with most money transfers between banks there will be days between these two). So they can just debit your account, check whether this has worked and then send the money on its journey afterwards and be done with it. If a bug happens and the money does not show up at the recipient, they will complain, the bank can look into it and fix it - no (or not much to the bank, anyways) harm done.