What type of memory retains data using battery power after the PC is turned off?

The correct choice is CMOS RAM. This type of memory retains data when the power is turned off because it is powered by a small battery on the motherboard, which ensures that the information, such as BIOS settings and system configuration, remains intact even when the computer is not in use. CMOS RAM is specifically designed for this purpose, allowing it to store critical system data without being dependent on the main power supply.

While other types of memory—like RAM and ROM—serve important functions in computing, they do not retain data in the same way when the power is turned off. RAM, for instance, is volatile memory, meaning it loses all stored data when the power is lost. ROM, on the other hand, is non-volatile and retains data but is typically used for firmware and not for dynamic system configuration. Flash memory, while also non-volatile and capable of retaining data without power, is not used specifically for storing BIOS settings and is generally utilized for storage purposes, like in USB drives and solid-state drives.