Disk array space issues

Hi guys.

I just bought a HP Proliant DL320n disk array for use as a backup server. It has 2 146GB disks and 4 750GB SATA disks.

The two 146 GB's are in one array with RAID 0+1 for the OS and apps.
The four 750 GB's are each in their own array (no fault tolerance of course) with one logical drive to use all the space.

My problem is that when I create a logical drive for the array, it maxes out at 719GB instead of 750GB. Why isn't it pulling in the extra 31GB?

So I can kind of let this go... but when Windows picks up the drives, it only recognizes 698GB of the 719GB that should have been 750GB to begin with. Where did that go??

So in total I've lost over 200 gigs. Does anyone know where all the space went? Is it a limitation of my Controller card? (Smart Array P400).

Thanks for the help!!
Tim

Just to elaborate on CJL's correct response (it goes beyond windows), the computers measure sizes in powers of 2 for exabmple a gigabyte is 2^30 or not the more common meanining of giga (1000000000). It leads to a descrepincy, which is why there is a disclaimer on every hard drive sold nowadays (formatting may lead to smaller size displayed), after a lawsuit was filed against all the drive makers.