Usually one makes the conversion using DriveSetup 1.7.3 by re-initializing the whole disk, which of course destroys all the existing data on the drive, which is probably what you don't want to do. Also, OS 8.1 is the first MacOS to use HFS+. However, Alsoft, the makers of DiskWarrior and of PlusOptimizer, also makes a program which will let one convert from HFS to HSF+ without reinitializing. You could read about this by going to their website, www.alsoft.com. I've never done this and don't have this program, but I'm sure one could google information about this. The Alsoft people provide technical help which is good, too.