Notation (was: The "swap rule" in chess...)

Larry Tapper wrote:
> "Ed Murphy" <[EMAIL PROTECTED]> wrote in message
>> ObEasyFollowup:  Why did I choose P-KB3?
...
> if you were playing White and I could choose your first move, I might
> pick P-KR4.

Can you please tell me what notation that is? Is P-KB3 äquivalent to b3?
Then why the redundant way of notation?
Thanks.