Every drive on PC is allocated letter. "C" is general for main hard drive, and letters generally ascend alphabetically from there A and B mechanically allocated to floppy disk drives. But you can assign own drive letters yourself from C to Z. This is useful if you are adjust to new PC that has different set of drive letters as last one you can set all drives to match with earlier.
• Go to Start and choose "Control Panel".
• Click "Administrative Tools". Choose "Computer Management”. Choose "Disk Management".
• Right tick drive you would like to modify and pick "Change Drive Letter and Paths."
• Select "Change," then select drive letter from list. You can only choose available, unallocated letter. Click "OK" to save modified settings.
• Go to Start and open "My Computer". Check below hard disk to double check that new drive letter has allocated and identified by system.