Stability was inconsistent and improved with successive public beta releases. Any problematic legacy program that would normally cause Mac OS 9 to crash could be contained and only require relaunching of the Classic environment without bringing down the main system.ĭuring beta testing of Mac OS X, the minimum version of classic Mac OS to be supported was 9.0.4, which needed to be installed separately. During its early development under the code name Rhapsody, a proof-of-concept called ' Blue box' demonstrated that backwards compatibility could be provided through a native application that would run the older software in a sandbox environment.
Mac OS X is based on NeXTSTEP, which uses a Unix-based kernel that is inherently incompatible with classic Mac applications.
