Abstract: A workpiece transporting apparatus particularly adapted to allow a rapid transfer of workpieces through a sealable opening between opposite sides of a wall, and thus rapid loading and unloading of vacuum processing or other sealable chambers. In a preferred embodiment, the apparatus employs a walking beam accumulator which comprises a first frame having a beam or rack with a series of locations for supporting a group of substrate holders, and a similar second frame mounted for rotation on an eccentric so that each holder supported by the first frame is removed, moved forward, and placed into an adjacent location on the first frame. The apparatus also employs a mechanism for relatively moving the walking beam accumulator and a workpiece receiver between a first position in which the wall opening can be sealed and a second position in which workpieces can be transferred between the accumulator and the receiver via the opening. In a preferred embodiment, the receiver is a rotatable drum inside a process chamber.