What is the system designed for one user that processes data quickly called?

The correct choice is microcomputer. A microcomputer is specifically designed for individual use and is built around a microprocessor, which is a single chip that processes data quickly and efficiently. This type of computer typically includes a CPU, memory, and input/output interfaces, all integrated into a compact form that is suitable for personal or small business tasks.

Microcomputers are capable of running a variety of operating systems and software applications, making them versatile for everyday tasks such as word processing, internet browsing, and gaming. Their design prioritizes speed and efficiency to serve the needs of a single user effectively.

In contrast, a workstation generally refers to a more powerful and specialized type of computer used primarily for technical or scientific applications, while a mainframe is designed for large-scale computational tasks and can support multiple users simultaneously. A notebook, or laptop, is a portable version of a microcomputer but is more focused on portability than the rapid processing capabilities typical of traditional desktop microcomputers.