Get Info-Why HD capacity isn't the same as HD's spec?

Ok, I'm stumped as to why is this.

My macbook came with an 80 gig hd. So why in the 'get info' does it say its capacity is 74.21 gigs?

The same with my external drive. I bought it....a 250 gig drive. So why when I use 'get info' it tells me its capacity is only 232.74 gigs??

Now this is not supposed to have anything to do with whatever was installed on these drives, yes?

Don't tell me drivers are eating up all that space.

My external came with a bit over 1 gig in "extras". So if its advertised as 250, were the heck is the missing 18 gigs? 18 gigs missing? Thats the size of my recording drive on my old system! Thats alot.
On the Apple drive.....where the missing 6 gigs? I don't get it.

Thanks
Jon

There ya go. You've answered my question. You guys are the BEST!

Thanks