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As I heard, it is still used even in some official places too. Sometimes I also still use it, but the Windows 3.11 version.

Ok... but do they compatible with current hardware?
Or they use the old hardware itself.

Probably they use old hardware, including embedded systems, but I do not know certainly. The DOS system is usable on modern hardware too, so the Windows 3.1/3.11 is probably also usable on modern hardware.