The Subst Drives tab allows you to specify mappings between drive names and source code locations
There are no mappings set up by default:

Substitute drives
•Add 
 adds a row to the Subst Drives table 
 enter the name of a disk drive in the Drive column 
 click in the Path column 
 enter the path that is to be used to substitute for the drive name 
For example, you might enter X:\ for the drive and e:\version2_1\release for the path.
You can double click to edit drives and paths in the table, or remove items:
•Remove 
 removes selected substitutions from the list 
Alternatively, press 
 to delete selected items, and 
 + 
 to select all items in the list first.
Reset All - Resets all global settings, not just those on the current page.
Reset - Resets the settings on the current page.