Internal Table creation

Hi Friends,

I have a question..We can create internal tables in 2 ways:

1. Data:Begin of itab,

-

end of itab.

2. Types:Begin of itab,

-

-

end of itab.

types: myitab type standard table of itab.

data:int_tab type myitab.

what is the differenc ebetween two?

thanks