Before the internet, how did different branches of the same bank know how much money you had in your account?*
To be honest, Internet has very little to do with visibility into account balance across different branches of a bank.
Many banks have had this capability years before Internet went mainstream.
Some banks don’t have this capability even decades after Internet has gone mainstream.
Internet has democratized connectivity for the common man but, well before it went mainstream in business, banks – and retailers and companies in many other industries – have used dedicated leased lines and other WAN links to establish connectivity between their branches / offices.
Once banks computerized their core banking operations, it was possible for most branches of a given bank to know the account balance of all their customers regardless of the branch in which the actual account was held.
The key to the said capability is “Core Digitalization”. It happened in some banks in developed countries via mainframe computers 30–40 years ago. It happened in some banks in developing countries via minicomputers 10–20 years ago.
While connectivity of different branches – via Internet or dedicated leased lines – is necessary to acquire the said capability, it’s far from sufficient.
In Are Digital Natives Losing Their Data Chops?, I gave the example of a bank in Germany where account balances were not visible to different systems in realtime.
It also reminds of an experience I had with my bank in Germany in the early oughties. The bank’s ATM would continue to display the same account balance even after I withdrew cash from it. To see the latest balance, I’d have to insert my debit card into a separate machine and print out the statement. The ATM reflected the latest balance only on the next day. Apparently, the bank’s core banking system that computed account balances sent out the updated information to the statement printing machine in realtime but only in batch mode (once a day at midnight) to the ATM network.
*: This is the original question I answered. I’m repeating it to help me make sense of my answer in case it’s moved to / merged with some other question that I didn’t answer.