The reason that only adds up to 150gb is because that is the formatted size of the hard disk. 160gb is the size before it is formatted.
Er, not quite. The factor you haven’t mentioned is that while most of the world thinks of one GB as being 1024MB, the hard disk industry thinks of it as being 1000MB.
In fact – and worse still – whenever the rest of the world thinks binary 1024, the hard disk industry thinks decimal 1000, so this creates an even more false upsizing of claimed hard disk sizes.
Feast on this less-than-easy-to-digest Wikipedia piece: