During a reboot, a server displays an OS not found error message. Which of the following is the most likely cause?

Resource exhaustion refers to CPU, memory, or storage capacity being depleted during runtime and would not produce an 'OS not found' message during early boot.

Excessive file system fragmentation degrades disk read performance but does not prevent the bootloader from being located or cause an 'OS not found' error.

A degraded RAID array may produce RAID controller warnings or slower performance but typically still presents a bootable volume unless a drive critical to the array has completely failed.

The BIOS/UEFI boot order defines the sequence in which the firmware searches devices for a bootable partition. If the boot order is incorrect - for example prioritizing an optical drive, USB, or network adapter over the OS drive - the firmware will exhaust its list without finding a valid bootloader and display 'OS not found.' Correcting the boot order to place the OS drive first resolves the error immediately.