What is MOSSYS: and SYS:MorphOS?
MOSSYS: is an assign pointing to SYS:MorphOS. The idea is that SYS:MorphOS is a private directory for the operating system and you don’t need to touch anything in it. A system upgrade will be done by simply putting a new directory (old one can be renamed or so). If you want to change the way the system is started edit s:user-startup, nothing else.