Is keeping the primary hard disk as disk C: still relevant?

"Your computer can use up to 26 drive
letters, from A through Z. Use drive
letters C through Z for hard disk
drives. Drive letters A and B are
reserved for floppy disk drives.
However, if your computer does not
have a floppy disk drive, you can
assign these letters to removable
drives.

From the allknowing Microsoft Knowledge Base

Before you modify drive-letter assignments, note the following items:

Changing the drive letter of the system volume or the boot volume is not a built-in feature of the Disk Management snap-in.
Many MS-DOS-based and Microsoft Windows-based programs refer to specific drive letters for environmental or other variables. If you modify the drive letter, these programs may not function correctly.

How to remove a drive letter

To remove an existing drive letter on a drive, on a partition, or on a volume, follow these steps:

Log on as Administrator or as a member of the Administrators group.
Click Start, click Control Panel, and then click Performance and Maintenance.
Click Administrative Tools, double-click Computer Management, and then click Disk Management in the left pane.
Right-click the drive, the partition, the logical drive, or the volume that you want to assign a drive letter to, and then click Change Drive Letter and Paths.
Click Remove.
Click Yes when you are prompted to confirm the removal.
The drive letter is removed from the drive, from the partition, or from the volume that you specified."

"You would be amazed at how many freshly developed, ""cutting edge"" applications assume c:\ to be the primary hard disk.

The convention may be outdated but guys who write the apps are still pretty ""dated"" for lack of a better word :)

My recommendation? Keep the C:\"

"Considering XP was around when floppy's were the thing, it is still the mainstream OS even though it is around 8-9 years old. So I guess I'm not that surprised that A and B are still skipped.

I remember someone at high school saying that they installed their windows instance on D: instead of C: so he couldn't get attacked or get viruses. I didn't have the heart to tell him about windows system variables (like windir and systemdrive). =)"

I think it falls under the "if it ain't broke...". I don't see any real advantage to changing the conventions and it would break a few old (some would say obsolete) assumptions. Pretty much a non-issue all the way around...

As best I can tell, the drive letters A & B have been reserved for backwards compatibility. Even though A: and B: are not in use, disk manager will not let you select either of those drive letters for your main boot partition. But I do agree with your point. A and B are no longer used so perhaps it is time for those folks at MS to jiggle the handle so to speak.