Exercise 2: Why grub-install's Target Differs Between BIOS and UEFI — Possible Solution
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Explanation:

Per the chapter's own explanation, this difference exists because BIOS
and UEFI genuinely write GRUB to disk in two structurally different
ways, echoing grub1-5's own material on the two firmware models. On
BIOS, grub-install /dev/sdX writes boot.img directly into the MBR's
own boot sector on the WHOLE disk device -- there is no filesystem or
partition-level concept involved at this step, just raw bytes written
to a fixed physical location at the very start of the disk, which is
exactly why the command targets the whole device rather than any
specific partition.

On UEFI, grub-install --target=x86_64-efi --efi-directory=/boot/efi
--bootloader-id=GRUB does something entirely different: it writes a
real GRUB EFI binary as an ordinary FILE inside the FAT-formatted EFI
System Partition (specified via --efi-directory), and separately
registers a new entry in UEFI's own persistent NVRAM boot list
(labeled via --bootloader-id) so firmware knows this new bootloader
exists and can be selected. This is a filesystem-level operation on a
specific partition, plus a separate firmware-registration step --
genuinely nothing like writing raw bytes to a disk's first sector.

Because the two mechanisms accomplish "install GRUB" in fundamentally
different ways -- raw sector write vs. file-plus-NVRAM-registration --
grub-install needs to be told explicitly which one to perform, which
is exactly what the --target flag and its accompanying arguments
specify.

WHY THIS WORKS AS AN ANSWER
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This explains the actual mechanical difference in what each command
writes and where (raw MBR bytes on the whole device vs. a real file
plus an NVRAM entry), directly tying the syntax difference back to
grub1-5's own BIOS-vs-UEFI material rather than treating the two
commands as arbitrary syntax variations.