The original DLL call interface had limited facilities, since it was expected that all the external entry points being called would have been written to meet the requirements of the interface. When calling a subroutine written in 'C', all the parameters being passed are sent by reference, that is a pointer to the value. This limited interface resulted in the need for small 'wrapper' routines to be written to interface to standard Operating System functions. The extended call interface, which is available within the declaration of a 'function' enables parameters to be passed by value and reference, plus handles additional 'C' data types. Using the extended call interface normally avoids the need to write the 'wrapper' routines.