I think you are referring to one of the many GUI's that are available on the internet for JkDefrag, made by other people. JkDefrag by itself does not have a drop down menu. MyDefrag also does not have a drop down menu. At the moment nobody has made a GUI program for MyDefrag, yet, so the only way to run for a single disk is through the native methods offered by the MyDefrag core. For more information see How to run MyDefrag for a single disk?