The sentence is speculating about the future development of computers by making a comparison with older technology. Without wires, telephones became smaller and more portable, and without horses, vehicles became faster and more convenient. But the author states that these technologies, once changed, did not simply continue to fulfil the same function as before, but took on new functions and gave people new possibilities. So, looking at the future of computers, we understand that fixed screens/monitors, keyboards and other peripherals will probably become unnecessary. Moreover, the author implies that these and other changes will allow the personal computer to evolve to the point where its functions are unimaginably more powerful and useful than they are today.

Mobile phones are more than existing phones without wires, and cars are more than carriages without horses. So computers without screens and keyboards, have the potential to be more useful, powerful and ubiquitous than people can imagine today.