WHY AREN'T KEYBOARDS IN ALPHABETICAL ORDER?

We always see our keyboard and only 1 question arise that why aren't keys arranged in alphabetical order. So what is the reason behind it. Why these keys are not arranged in alphabetical order. What is the history behind it? 

ANSWER :-

This goes back to the original manual typewriters. The keys were originally arranged based on most common letter usage, but people typed so fast the mechanical character arms would get stuck together. So the keys were placed in positions to actually slow people down. 

The Dvorak keyboard came out in probably the 80s and is based on the most common letter usage idea again now that people do electronic word processing rather than "typing". 

The QWERTY keyboard layout was devised and created in the 1860s by the creator of the first modern typewriter, Christopher Sholes, a newspaper editor who lived in Milwaukee. Originally, the characters on the typewriters he invented were arranged alphabetically, set on the end of a metal bar which struck the paper when its key was pressed. However, once an operator had learned to type at speed, the bars attached to letters that lay close together on the keyboard became entangled with one another, forcing the typist to manually un-stick the type-bars, and also frequently blotting the document. 

A business associate of Sholes, James Densmore, suggested splitting up keys for letters commonly used together to speed up typing by preventing common pairs of typebars from striking the platen at the same time and sticking together. The effect this rearrangement of letters had on maximum typing speed is a disputed issue. Some sources assert that the QWERTY layout was designed to slow down typing speed to further reduce jamming. Other sources assert the rearrangement worked by separating common sequences of letters in English. Ostensibly, the hammers that were likely to be used in quick succession were less likely to interfere with each other.