What was the first modern transaction processing system?

The cash register is recognized as the first modern transaction processing system because it was one of the earliest devices used to record sales transactions electronically. Developed in the late 19th century, the cash register automated the process of recording sales and calculating totals, which significantly improved the efficiency and accuracy of financial transactions in retail settings. This development marked a pivotal shift from manual record-keeping to more systematic and effective transaction processing, laying the groundwork for more advanced systems that followed.

Other options represent advancements in transaction processing that came later. Electronic data interchange, while crucial for business communications, is not specifically a transaction processing system in the way a cash register is. Point of sale systems evolved from cash registers and incorporate more features but came about after the introduction of the basic cash register. Online payment gateways are modern mechanisms that facilitate online transactions, further reflecting the evolution from the basic functionalities established by the cash register.