From my point of view, banks make money through the services they render to we the customers who save our money with. As we save with them, they deduct a certain amount of money from our savings. Again, banks lease out the money customers save with them and through that, they gain some interest from loaning out money to others. Customers are being charged some fees for using banks' resources such as the automated teller machines and others.
They also make money out of interests, just like you said with loaning. They are using that to their advantage. I'm not sure if they have a central server dedicating,
the information they have on people but knowing such information would be crucial from them, they would know who has money and who does not have.
Most of the banks money is just virtual - they do not exist. Banks make most of their money on interest differences between deposits and loans, they collect another large portion for just running bank accounts. There is still a large part of what they trade when they keep the money transferred from the account to account - yes - all delayed transfers mean that the bank uses your money to trade on exchanges with currencies.
I think it's just numbered with corresponding users with what amount they have on an account, whether it is a savings type or a checking account, whatever.
They are the ones collecting a lot of money and they use that to invest in other ways, having a large sum amount of money could really be why banks are so strong.
Everything now is all about money, taking advantages of other people to profit from. Thankfully Bitcoin was invented.