[Haskell-beginners] Meaning of '!' in record defintion? UNPACK?

[Colin Paul Adams]

>>>>> "Thomas" == Thomas Davie <tom.davie at gmail.com> writes:

    Thomas> The {-# UNPACK #-} tells the compiler that it can unpack
    Thomas> the Int – meaning that a Position will be neatly packed
    Thomas> into 12 bytes.

What would be the difference if there was no UNPACK pragma?
-- 
Colin Adams
Preston Lancashire