Just to clarify what this is, it is the complete studio recording sessions that Charlie Parker did for a group of small record labels in the 40's such as Savoy, Guild, Mercury, Dial, Clef, Norgran...generally these have come to be known as the Savoy and Dial recording sessions. These cuts contain the music that made Charlie Parker a legend and, indeed, changed the course of jazz music. They also contain work of a number of other masters like Dizzy Gillespie and Miles Davis; many of these recordings were originally with other musicians as the leaders of the sessions but they have come to be treasured because of the work of Charlie Parker on them. 　　This is a "complete" set of the recordings, meaning that it not only contains the "master" recordings that were released to the public but also the alternate takes. Alternate takes are often complete takes that were judged not quite as good as the version that released...or they may be false starts, takes plagued with a few errors, or takes with small technical problems. At any case, these alternates give you a chance to hear Bird and his sidemen working through numbers, perfecting approaches, and trying out different improvisations.