Ask HN: How OS detect keyboard layout?

I was just build GH60 keyboard, and set the key using this dvorak layout here http://www.keyboard-layout-editor.com/#/gists/2f5956676fb8761a4fe504d32e118470. It works perfectly on qwerty layout in windows and linux, but not detected as dvorak keyboard and doesn't work in dvorak layout.

It is make me wondering how the windows or linux detect keyboard layout?