Which area is the first read by UEFI or BIOS during boot?

The boot process in UEFI or BIOS begins by examining the boot sector of the storage device. The boot sector contains critical information that helps the system identify the storage medium and the structure to look for the boot loader. This area is specifically designed to facilitate the execution of the operating system. The firmware reads the boot sector to decide the next steps in the boot sequence, such as launching the operating system or invoking the boot manager.

The other options do not serve the same foundational role during the boot process. For instance, the operating system partition holds the operating system files but is accessed later in the boot sequence after the boot sector has been executed. The file system table and root directory are also part of the operating system's file structure, but they are not directly accessed during the initial stages of the boot; they come into play once the operating system takes control and starts accessing files. Thus, the boot sector is the critical area that the firmware looks at first when booting the computer.