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Versions 10.0 through 10.8 of this Operating System used various "Big Cats" as the code names for new versions before switching to "Landmarks"
What is Apple
– i.e.
Version 10.0: "Cheetah"
Version 10.1: "Puma"
Version 10.2: "Jaguar"
Version 10.3: "Panther"
Version 10.4: "Tiger"
Version 10.5: "Leopard"
Version 10.6: "Snow Leopard"
Version 10.7: "Lion"
Version 10.8: "Mountain Lion"
Version 10.9: "Mavericks"
Version 10.10: "Yosemite"
Version 10.11: "El Capitan"