Due to the fact that GameMaker: Studio is focused on fast
cross platform development, there are a number of functions that
were available in previous versions of GameMaker that are
now no longer supported. Most of these have been removed to permit
games to run on devices without them blocking, but some have been
removed because they are obsolete with current technology, or
because they are specific functions for Windows that are no longer
necessary.
Explaining exactly why each of these features was removed, as well
as suggesting any possible workaround for you, is outside of the
scope of this manual, but you can find a list of all the functions
and functionality that has changed between Legacy versions and
GameMaker: Studio here: YoYo Games Knowledge Base - Porting GM7 And GM8
Games To GameMaker: Studio.
Each of the following pages details the functions that have been
removed and gives a brief explanation as to why they have been
removed: