OS 9.1 is the final version of the 'Classic' style Mac OS (as Apple has dubbed it). It represents the pinnacle of stability and user-friendliness of the old-style operating system.

However, this isn't saying much. OS 9.1 is just the old system with a few enhancements and some re-coding to make way for OS X. It has the same problems that have plagued Apple for years. Macs running OS 9.1 or earlier probably crash just as often as Microsoft Windows-based PCs, due to poor memory management and too many loaded extensions, among other reasons.

As an upgrade, Mac OS 9.1 doesn't represent very good value. The simple reason for this is that it's actually included free with Mac OS X for compatibility with older applications, since Mac OS X is currently a bit starved of third party software.

Our advice? Buy Mac OS X and get OS 9.1 free. This way, you can set up a dual boot system easily and either boot into OS 9.1 or run it from within OS X.