Unlike previous upgrades, there were no compatibility issues with the new operating system.

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Microsoft's Windows 95 has dominated the U.S. desktop market because of its compatibility: users buy the operating system that has the most software available, and third-party developers produce software for the system that has the most users.

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It's a compelling proposition: all the power and application compatibility of a laptop running a proper desktop operating system, all the portability and convenience of a tablet, all mixed together in one package.

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Linux, the "open-source" pc operating system, has a different sort of cultism, one more disposed to compatibility.

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Bug-for-bug compatibility is a problem, but breaking backward compatibility would be a much bigger problem, so even as the lowest layers of the operating system are revised and rewritten, the layers that applictions talk to (the application programming interface, or API) are carefully tested to ensure that no changes are visible to the application.

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