Final answer:
The startup instructions needed when a computer is powered on are stored in the BIOS, which is firmware on the motherboard. It is responsible for hardware initialization and bootstrapping the operating system. The correct answer is a) BIOS.
Step-by-step explanation:
The component that holds startup instructions needed when the computer is powered on is the BIOS (Basic Input/Output System). The BIOS is firmware embedded on the motherboard of a computer and is the first software that runs when a computer is started. It initializes and tests the system hardware components and loads the operating system from a hard drive or other bootable devices.
The correct answer to the question is: a) BIOS. The other options such as b) CPU (Central Processing Unit), c) GPU (Graphics Processing Unit), and d) SSD (Solid-State Drive) do not hold the startup instructions. The CPU processes all instructions once the computer is on, the GPU handles graphic processing, and the SSD is a type of storage device that may contain the operating system but does not itself hold the startup instructions.