The workbench program itself in AmigaDOS wasn't written as a multi-threaded app. There are various workbench substitutes that are multi-threaded as far back as the pre workbench 1.3 jazzbench. Just lookup the aminet readme's on various workbench substitutes. It was considered a nice feature to implement because folks got tired of things taking so long to load in one window when all they wanted to do was open the next drawer inside the first one they opened, or waiting for one copy to finish to start another one. Multi-threading a file manipulation program (and GUI program launcher) does make the program more complex due to possible race conditions when various threads are working with the same filesystems at the same time along with filesystems which weren't necessarily notifying clients of changes happening underneath them and the client programs making presumptions that things weren't changing.
