Is the desktop OS obsolete due to easy-to-use interfaces like in a mobile OS?

I do not think so. There are a lot of things that are still very difficult to do in a mobile or touch based OS. For example image editing is painful to do well on a touch device, especially if you are looking for accuracy. Imagine trying use Photoshop on a smartphone! However, I have seen people use Photoshop on a Surface but they always use another tool such as a stylus or a mouse.

On the other hand touch OSs do a lot of things better such as low power consumption and being fast most of the time but these can never be trade offs for a lot of the things that desktops do a lot better.

Slightly off the topic here, a powerful device which was touchscreen but also had capabilities to connect to a mouse and keyboard would be a great option for many people. Also when you plugged a mouse in, the UI would change to better suit a mouse. Surfaces have a lot in common with this imaginary device but they are still very heavy and do not have much RAM.

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