>>>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
>>
>>
>>In each case, the first one is single, or one OS, DS, SA. The second one is multiple. For example, 2 or more Operating Systems (NT, Windows 95). The same for DA & SA.
>
>Thanks Craig,
>
>I may look stupid to ask this question. However, I learned to use a singular form of a word to be used as an adjective, for example, we say: he is a horse rider or a car repairman. On the other hand, I would say I am a systems analyst and I do systems analysis and systems design. So you native speakers feel it is ok or even preferable to use the plural form, systems, instead of a singular form, system, in these cases.

Not stupid at all. Learning another language, especially English is not easy. We use plural form when it is needed...when we are discussing multiples. Singular and plural are both nouns.