An sdev file extension is related to the Apple System 7 Control Strip module file format.
SDEV file extension - Apple System 7 Control Strip module
What is sdev file? How to open sdev files?
File type specification:
The sdev file extension is associated with the Control Strip a user interface component (like Dock in OS X) integrated in Apple System 7 operating system. The *.sdev file stores module for Control Strip stored in System Folder ("Control Strip Modules").
Apple System 7 is obsolete system replaced by Mac OS Classic and OS X.
This sdev file type entry was marked as obsolete and no longer supported file format.
This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.