Have you ever wondered why the PIN on ATM cards is exactly four digits? The truth of the matter, from the man who built the very first machine:
The first automatic teller machine, now known as ATMs, was installed at a branch of Barclays Plc in a north London suburb on June 27, 1967.
Plastic bank cards had not been invented yet, so [John] Shepherd-Barron’s machine used special checks that were chemically coded. Customers placed the checks in a drawer, and after entering a personal identification number, a second drawer would spring open with a 10 pound note.
Shepherd-Barron originally planned to make personal identification numbers six digits long, but cut the number to four after his wife Caroline complained that six was too many.
“Over the kitchen table, she said she could only remember four figures, so because of her, four figures became the world standard,” he told the BBC.