What does C drive indicates?
The default annotation C: typically refers to the primary hard
drive or primary partition of a hard drive from which the operating
system is booted. The reason it is typically the C: letter drive is
that, back in the day, a 3.5" disk drive was annotated as A: by
default and the 5" or floppy drive was annotated as B: by default.
The drive letter D: is usually utilized to indicate the default
annotation of the primary optical (cd-rom or dvd-rom) drive of the
computer.
Due to the creation of hard drive partitions, (or devisions of a
hard drive to create virtually separate drives) it is possible for
one hard drive to have multiple drive letters typically ascending
in letter from E: (Drive C: Primary Hard Drive Drive D: Primary
Optical drive. Drives E:, F:, G:, etc secondary hard drives which
are also known as slave drives.) Windows is capable of customizing
the drive letter annotations to suit the user, (including the
primary drive annotation of C:) which is why this is not universal
for all computers. However, for Windows, the primary hard drive
from which the operating system is booted is always annotated as C:
by default. If the drive letter has been changed in the operating
system only, a menu will typically pop up on boot up on at least
one occasion asking for the drive letter of the hard drive on which
the operating system is loaded. (Unless the motherboard settings
are changed, the motherboard will automatically try to boot the
operating system from drive C:)