WinPE: Identify drive letters with a script
WinPE drive letter assignments change each time you boot, and can change depending on which hardware is detected.
You can use a script to figure out which drive letter is which by searching for a file or folder.
This sample script looks for a drive that has a folder titled Images, and assigns it to a system variable: %IMAGESDRIVE%.
@echo Find a drive that has a folder titled Images.
@for %%a in (C D E F G H I J K L M N O P Q R S T U V W X Y Z) do @if exist %%a:\Images\ set IMAGESDRIVE=%%a
@echo The Images folder is on drive: %IMAGESDRIVE%
@dir %IMAGESDRIVE%:\Images /w