Virtual Directory Support is not related to virtual() but to the actual implementation of some file/directory macros used by zend/php and some php modules.
Virtual Directory Support off -> php relies on the c library functions for resolving the current working directory
Virtual Directory Support off -> php uses the tsrm implementation that keeps track of the current working directory on a per thread level.
oops, copy&paste error.
Virtual Directory Support on -> php uses the tsrm implementation that keeps track of the current working directory on a per thread level.