As part of a system for processing workpieces, a workpiece support arrangement, separate from a process chamber arrangement supports at least two workpieces at least generally in a stacked relationship to form a workpiece column. A transfer arrangement transports at least two of the workpieces between the workpiece column and the process chamber arrangement by simultaneously moving the two workpieces at least generally along first and second transfer paths, respectively, that are defined between the workpiece column and the first and second process stations. The transfer arrangement can simultaneously move untreated and treated workpieces. Vertical motion swing arms and coaxial swing arms are described. A pair of spaced apart swing arms, the workpiece column and the processing stations can cooperatively define a pentagonal shape. Timing belt backlash elimination, a dual degree of freedom slot valve and low point chamber pumping, for removing chamber contaminants, are also described.