Money & WorkHow it works
How a card payment travels halfway around the world in a second.
Typing your PIN starts a relay race: the terminal sends amount and card data to the merchant's service provider (acquirer). It forwards them through the card network (Visa, Mastercard, a national debit scheme) to your bank (issuer), which checks balance and limit and replies "approved" in about a second. Booking comes later: settlement runs in batches, usually next business day.
Useful: That's why the amount often shows up in your account days later even though the payment went through instantly.
Source: en.wikipedia.org