I ma not a native English speaker. However, I have to use English to do reading, thinking and a lot writing. After years working in the computer tech World, I still cannot tell what is the difference between the words 'System' and 'Systems' in cases such as:

Operating System v Operating Systems
Database System v Database Systems
System Analist v Systems Analist
...

I would appreciate anyone who cares to offer an English lesson.

Chen