Typing exams is better than handwriting?

Why can't students type their exams
under normal exam conditions?

I am thinking that we should allow our students to type their theory examinations. At work we have the facilities to lock the machines down so they can't communicate, block the net, limit USB access or do anything other than type in Word. 

It might be an optional thing. Students that WANT to type, can. Those that WANT to write, can. That way there is no penalty from switching from one system to another. A friend has raised the issue that the examiner (ie myself) may have a bias towards marking the typed essays.I personally don't feel that way because already as it is, some students have clear hand writing and others do not. Unless I really can not read what is written, I don't penalize messy hand writing. And there certainly isn't any bonus to writing crap responses in beautiful and clear script. 


My only concern would be, what would be the educational impact of this??