system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When and how did banks switch from actual paper money to the computerized system they use today?
gpt
Banks have never really dealt with actual money.  They take your paper cash, write down in a book that they have $100 of your dollars... then loan $100 to someone else.

The bank now has 0 dollars on hand.  It owes you $100.  Some other guy owes them $100.

They make money because the bank told you it would give you $5 if it could have your $100 for a month.  It told the other guy it could have $100 if the guy paid them back $110 in a month.

At the end of the month, if the guy pays it back and you want all of your money, the bank has $5 more than it did before all this started.