For the most part, I'd say Apple's compatibility efforts have been equally impressive: * 'Classic' support enabled Mac OS 9 apps to run on OS X for many years.

For the most part, I'd say Apple's compatibility efforts have been equally impressive: * 'Classic' support enabled Mac OS 9 apps to run on OS X for many years. * Rosetta allowed for apps written for a completely different processor architecture to run on Intel (until 10.7, aparently). Apple also made these moves before the bulk of 3rd-party applications were running natively on the new systems/architectures. The fact that Apple has been able to change low-level OS & processor architectures over the past 10 years is quite a feat.