Final answer:
The first step in the boot process is the Power-On Self-Test (POST), which tests essential system components before the system BIOS proceeds with the boot.
Step-by-step explanation:
The first step in the boot process is B) POST (Power-On Self-Test). This occurs immediately after the system is powered on. The POST is a diagnostic testing sequence run by a computer's firmware to ensure that all essential system components are present and functioning correctly before the BIOS begins the actual boot. If any errors are detected during POST, the system will usually halt the boot process and give an error message or a series of beeps to indicate the problem.
After POST, the system can proceed to step C) Reading the master boot record, which in turn leads to step A) Loading the operating system. Initializing peripheral devices, D), is also part of the process, but it occurs later on.