rhapsody's blue box environment, available only when running on the powerpc architecture, was responsible for providing runtime compatibility with existing mac os applications. compared to the more streamlined and integrated classic compatibility layer that was later featured in mac os x, blue box's interface presented users with a distinct barrier between emulated legacy software and native rhapsody applications. all emulated applications and their associated windows were encapsulated within a single blue box emulation window instead of being interspersed with the other applications using the native yellow box api. this limited cross-environment interoperability and caused various user interface inconsistencies.