What type of device is primarily used to store a computer's system files and folders?

The hard drive is primarily used to store a computer's system files and folders because it serves as the main storage component in a computer system. It is designed to hold the operating system, application software, and user data, allowing for quick access and retrieval of files. Unlike USB drives, CD-ROMs, and flash drives, which can be used for supplementary storage or data transfer, the hard drive is integral to the computer's functionality, providing the primary space where the system files necessary for booting up and operating the machine are kept. Additionally, hard drives typically have larger storage capacities and are optimized for continuous use, making them essential for running applications and managing system resources effectively.