HDD problem

I've just recently switched to Mac and am now the proud owner of a DA Powermac G4 533. Given that the 30GB HDD currently running 10.3.9 is a little pokey I want to install a new maxtor 80GB 7200 2mb cache drive.

I've physically installed the 80GB drive and set it to slave for the time being. However Disk Utility only identifies the HDD as having 31.5GB rather than the full 80GB ? I'm not really sure why it's doing this. The drive has not been used before and so there were no partitions etc on it. I ran "Erase" on it hoping that it might free up some more space. But no change to total capacity unfortunately.

Any suggestions would be greatly appreciated.

P.S boot ROM version is 4.1.8f5