The process of starting or restarting a computer system is called:

The process of starting or restarting a computer system is known as Booting. This fundamental process involves the computer's initial set of operations when power is turned on or reset. During booting, the system performs a Power-On Self-Test (POST), loads the operating system from storage into the computer's main memory (RAM), and initializes all necessary hardware and software components, making the computer ready for user interaction.

• Loading (B) is a general term for transferring data or programs into memory, but it doesn't encompass the entire startup sequence.
• Formatting (C) is the process of preparing a storage device (like a hard drive) for data storage by creating a file system, which typically erases existing data.
• Processing (D) refers to the general act of a computer performing operations on data, which is a continuous activity, not just the startup phase.