Display simultaneous text

I would like to get the code where

" when you are typing in a text box ,another display box automatically displays the text that is being typed simultaneously".

Eg :- If i am typing America -As i type "A" in the 'text box' the 'display box' should display "A".Then as i type m after A ,the display box will show " Am" (original word and second word).Now as i type e after Am in the text box the display box should show "Ame".

I hope i am making it clear.

How do we do that.
Please suggest.

 

This is done via javascript not php

<script type="text/javascript">

function copyText() {
    document.getElementById('displayarea').innerHTML = document.getElementById('text').value;
}

</script>

<textarea id="text" style="width: 300px; height: 100px" onKeyUp="copyText();"></textarea>
<div id="displayarea" style="width: 300px; height: 100px; border: 1px solid #000;"></div>

Code (markup):

 

Thank you very much Mr.Stephan.That works!