What hardware component stores the macOS operating system?

The macOS operating system is stored on persistent storage devices, which include SSDs (Solid State Drives) and HDDs (Hard Disk Drives). These storage types retain data even when the device is powered off, making them necessary for holding the operating system, applications, and user data.

The RAM, while essential for temporarily holding data and allowing quick access during operation, does not retain information after a device is turned off and therefore does not store the operating system itself.

The circuit board is a critical component of the hardware structure and contains the essential circuitry for the device's operation but does not function as storage for the operating system.

The GPU is responsible for rendering graphics and accelerating visualization processes, but it does not store the operating system or data persistently. Thus, SSDs and HDDs are the correct answer because they serve as the primary storage mediums for the macOS system files and other data.