Final answer:
Airline Reservation Systems, Communication Networks, and Automated Teller Machines which require high reliability and availability typically use Mainframe computers. These systems are known for secure, massive data processing capabilities suitable for 24/7 operations, which is not the typical domain of personal computers, despite their own advancements. The correct answer is 1) Mainframe.
Step-by-step explanation:
Airline Reservation Systems, Communication Networks, and Automated Teller Machines, which must be operational at all times, typically use Mainframe computers. Mainframe computers are powerful systems that are capable of processing and managing vast amounts of data securely, reliably, and concurrently for multiple users.
Despite the popularity and improvements in personal computers, they do not match the continuous operational capacities of mainframes.
Mainframes have played a key role in computing history. For example, the semi-automatic business research environment (SABRE), which began as a connection between two mainframe systems, helped to shape early computer networks and airline reservation systems.
Over time, computing has become indispensable in various aspects of business and personal life, but for 24/7 operations with high reliability and transaction handling requirements, mainframes remain the system of choice.