TestOut LabSim A+ Certification 2026 – 400 Free Practice Questions to Pass the Exam

The CMOS battery is essential for saving system settings when the computer is powered off because it provides power to the CMOS (Complementary Metal-Oxide-Semiconductor) memory. This non-volatile memory stores BIOS settings, system time, and hardware configurations, which need to be retained even when the computer is unplugged. When the computer is turned off, the CMOS battery maintains these settings, allowing the system to boot up with the correct configurations the next time it is powered on.

In contrast, the power supply serves to convert electricity for the computer's components but does not store any data. The main processor executes instructions and performs calculations but does not maintain system settings. The hard drive is responsible for storing user files, applications, and the operating system but does not specifically keep the BIOS or system settings required for booting and system configuration.