Your operating system automatically assigns a drive letter for your main drive, which is usually C, so it saves you the trouble of choosing it yourself. As you install more drives and more devices, the letter allocation can become confusing, and it can actually cause problems with the drive installation; the USB drive or external will not appear due to the allocated letter already being used by something else.
Luckily you can overcome this problem before installing any new drive, or in case “My Computer” doesn’t display the drive you’ve just installed. It is simple enough to change the letter allocation for your hard-drive or secondary drive (usually the “slave”), and we will look at how to do just that.
A Word about Installation Paths
Since most installers will look for "C" by default (such as MSI installers for instance), it is helpful to know how to change this directory during the installation process. This is only needed if the drive you’ve reassigned is your main partition or the drive with your main Operating System.
Using the MSI installer as an example, you can change the path a couple of screens after you are guided through the process. After having clicked "next" a couple of times, a screen with "Select Destination Location" will appear: here you can select the drive-letter where you want the installation to take place.
Changing Drive Letter Allocation
The easiest solution in order to avoid problems with letter allocation, is to make your main hard-drive and your slave or secondary-drive (if you have one installed) Y and Z; this of course ensures that there are no allocation problems, unless you have a large number of drives installed, which isn’t likely.
The following applies to the Windows Vista operating system; the changes for XP are the same and you can follow the link below for help.
Click on the “Start” menu and go to “Control Panel”. Click on “Administrative Tools” (if you have classic view switched on, click on “System and Maintenance” first). Click on “Computer Management:” in the open window look on the left and find the heading “Storage.” Click on “Disk Management” under “Storage.”
Now you can change or re-allocate a drive letter. Right-click on whichever drive you want to change (i.e. C: or your primary partition for example); a drop-down menu will appear and you can choose “Change Drive Letter and Paths…” Click on Change and re-assign a letter by “Assign the following letter” and choosing on the right-hand side.
Here is an article for changes in Windows XP:
Remember that frequently re-allocating hard-drive letter can cause problems. In case of such problems you can run the "Disk Management Utility" or read the following article which deals with some of the problems which you can encounter:
Finally here are a couple of related BrightHub articles: