IT Dojo: Quickly map drive letters in Windows XP with SUBST, PUSHD, and POPD In this IT Dojo video, Bill Detwiler demonstrates three old DOS commands that making mapping folders and network shares a snap.First, Bill looks at the SUBST command. SUBST lets you quickly and easily map a local, nested folder to a drive letter. Second, he examines the POPD and PUSHD commands.