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real operating system: n.

The sort the speaker is used to. People from the BSDophilic academic community are likely to issue comments like “System V? Why don't you use a real operating system?”, people from the commercial/industrial Unix sector are known to complain “BSD? Why don't you use a real operating system?”, and people from IBM object “Unix? Why don't you use a real operating system?” Only MS-DOS is universally considered unreal. See holy wars, religious issues, proprietary, Get a real computer!