An optical disk "jukebox" mass memory system is being developed which will provide automatic access to any data in a store of 1013 bits within five seconds. This system contains a library of 128 optical disks with mechanisms for retrieving any disk, loading it onto a turntable, and recording or playing digital data at a rate of 50 Mb/s. The optical disks are housed in protective cartridges to facilitate handling by both the operating personnel and automatic disk handling mechanisms. Cartridges are moved from the store to a load station by a precision, belt-driven X-Y transport mechanism. The load station then mounts the disks onto a precision turntable where they are spun up to speed while still housed within their protective cartridges. Next, data is recorded or played back on these disks using focused laser beams. Finally, the disk is stopped and returned to its storage location so that the system can handle a new request. The disk handling mechanisms were designed to minimize mechanical shock and vibration while providing a rapid, smooth operation. A special centering hub design for the turntable minimizes disk eccentricities during multiple load/unload cycles and allows easy inter-changeability from machine to machine. This paper will describe the system, subsystem, and mechanism designs that were used in developing an engineering model of this jukebox concept. Test results from this engineering model will also be presented in this paper.