The correct answer is: A. COMMAND.COM, IO.SYS
When you turn on your computer, the BIOS (Basic Input/Output System) performs a power-on self-test (POST) to check the hardware and make sure it is working properly. If the POST is successful, the BIOS then loads the first sector of the hard drive into memory. This sector contains the boot sector, which is a small program that is responsible for loading the operating system.
The boot sector loads the operating system into memory and then transfers control to it. The operating system then takes over and starts running programs.
The operating system checks the following control files each time you turn on the power switch:
- COMMAND.COM: This is the command interpreter that allows you to type commands at the command prompt.
- IO.SYS: This file contains device drivers that control the input/output devices on your computer.
- MSDOS.SYS: This file contains configuration information for the operating system.
If any of these files are missing or damaged, the operating system will not be able to load and your computer will not start.