Why aren't keys arranged in alphabetical order on a keyboard?

Why aren't keys arranged in alphabetical order on a keyboard?

It was 1875, Christopher Sholes with assistance from Amos Densmore  rearranged the typewriter keyboard so that the commonest letters were not so close together and the type bars would come from opposite directions. Thus they would not clash together and jam the machine. The new arrangement was the "QWERTY" arrangement that typists use today.

On his first model, his "ABC" key arrangement caused the keys to jam when the typist worked quickly. Sholes didn't know how to keep the keys from sticking, so his solution was to keep the typist from typing too fast.


He did this using a study of letter-pair frequency prepared by educator Amos Densmore, brother of James Densmore, who was Sholes' chief financial backer. The QWERTY keyboard itself was determined by the existing mechanical linkages of the typebars inside the machine to the keys on the outside. Sholes' solution did not eliminate the problem completely, but it was greatly reduced. 
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The keyboard arrangement was considered important enough to be included on Sholes' patent granted in 1878, some years after the machine was into production. QWERTY's effect, by reducing those annoying clashes, was to speed up typing rather than slow it down.

The new arrangement was the "QWERTY" arrangement that typists use today. Of course, Sholes claimed that the new arrangement was scientific and would add speed and efficiency. The only efficiency it added was to slow the typist down, since almost any word in the English language required the typist's fingers to cover more distance on the keyboard.

                                                                                                           Source  : www.ideafinder.com