The ATA Hi-Cap Support Driver software was created to allow the use of extended capacity ATA drives (drives greater than 128 Gigabytes in size) on older (Pre-Mirrored Door) G4 and G3 Macintoshes -- including Cubes, PowerMacs, PowerBooks, iBooks eMacs and iMacs running MacOS X versions 10.2 and later.
Without this software installed, any extended capacity drive which is connected to the built-in ATA bus on older Macintosh models will be limited to only 128 Gigabytes. Later model G4's and all G5's and Intel Macs do not suffer from this limitation.
The ATA Hi-Cap driver package also includes an easy-to-use installation/removal utility.