How Windows Assigns Drive Letters
Last Updated: 27 Mar 2004
*** PLEASE NOTE: Link(s), If Provided, May Be Wrapped ***
Drive letters are automatically assigned by DOS and
Windows using certain criteria based on the type of
partitions of each physical disk.
For the most part, these default assignments can be
overridden. Here are some explanations concerning how
the determinations are made:
DRIVE LETTER ASSIGNMENTS
CHANGING THE SYSTEM DRIVE LETTER
Attempting to change the drive letter of an existing
installation of Windows (particularly NT and family) is
highly discouraged. It is not impossible (I've actually
done it before in NT4), but it is so tedious as to be
totally avoided. Not to mention, you'll be hounded by
weird problems for months... Many, many registry changes
to make, along with BOOT.INI and some other system files.
NOTE: If you're running Active Directory on the box in
question, don't even bother trying to change the
You're better off just reinstalling over the existing
installation to correct a drive letter change to the
OS. I honestly can't think of a good reason why this
is so difficult to change, but it is.
DRIVE LETTER ASSIGNMENTS DURING SETUP
To avoid the aforementioned problem of getting a letter
other than C: assigned as the system partition, it is
advisable that you always create a partition during the
setup process -- even if you intend to use the entire
drive as a single partition.
Doing it this way will enable you to see what letter
would be assigned to the partition. If the letter that
is provided is something other than C:, simply reboot
(after creating the partition) and run setup again. This
time, the correct letter will be assigned.
This happens most often if a ZIP drive is connected
during setup, or if you set a new drive as Master, and
the slave drive already has partitions on it. Rather
than disconnecting everything before installation (which
is one option), you can just make sure that you create
the partition(s) as mentioned above, and everything will
be good to go.
All that counts is the drive letter that is assigned
DURING the setup process.
MOVING DRIVES TO A NEW SYSTEM
DYNAMIC DISKS & DRIVE PATHS
Starting with Windows 2000, you can finally break the
26 drive letter barrier that has afflicted both DOS and
Windows for centuries.
Instead of drive letters, you get drive mount paths:
• Windows XP (both Home and Pro) behave just like NT and
2000 when it comes to drive letter assignments.
• In NT/2000/XP, I always manually set the drive letters
of all drives in my system (rather than simply relying
on the default assignments) so that the addition of a
new hard drive will not wreak havoc with my preferred
• If you add a second hard drive but create all of the
partitions as logical drives in an extended partition,
the drive letters of your primary hard drive will not
change, even if you haven't manually assigned them.
• I prefer the CDROM to be drive Z: (multiple CDs start
at Z: and work their way down) because it is much
easier to know that a CD will always exist at Z:, as
opposed to having to guess, depending on the number
of drives installed in a system.
RELATED TOPICS (ALSO IN THIS ARCHIVE)