Another interesting snippet is that originally, he wanted a 6 digit PIN. But when he asked his wife, she said that she can't remember a number more than 4 digit. And thus was the ubiquitous 4 digit PIN born.
Shepherd-Barron's principal motivation while inventing the machine was 24*7 availability of cash. However, it helped reduce the cost of a transaction greatly and replaced the human tellers rapidly. Today in India, the average cost of an ATM transaction could be as low as Rs 12 (majority of the cost going towards cash counting and transportation) while the cost of the same transaction if done through a teller clerk, in spite of the low salaries, could be Rs 50 or more. The difference between cost of cash dispensed by humans and the ATM machines in the more well economies such as UK or USA would be much higher.
It is quite possible that the plastic card itself or mobile payment products or another invention could obviate the need of an ATM machine in future and the ATM machine becomes but a footnote in the long history of financial innovation. But at the moment, this machine is the mainstay of the retail banking industry replacing the need of a branch with this machine. In fact, Paul Volcker, the former US Fed Reserve Chairman, described the ATM as the last truly great innovation in financial services