Which characteristic is essential for online transaction processing systems?

An essential characteristic for online transaction processing systems is the requirement for fault-tolerant computer systems. This is crucial because online transaction processing (OLTP) systems must handle a high volume of transactions in real-time, and any failure or downtime can lead to significant financial loss and disruptions in service. Fault tolerance ensures that the system can continue to operate smoothly, even in the presence of hardware or software failures. It allows transactions to be processed reliably, maintaining data integrity and availability.

In summary, the presence of fault-tolerant systems within OLTP applications guarantees continuous operation, safeguards against data loss, and preserves the user experience. This is why it stands out as an essential characteristic of these systems. Other options may be useful in different contexts but do not address the core operational needs of OLTP systems effectively.