RISO digital duplicators are categorized primarily by their color capabilities, resolution, and paper handling size. Models include single-drum systems (which print one color at a time, requiring manual paper re-feeding for multi-color jobs) and two-drum or multi-color systems (such as the MZ series, which can print two colors simultaneously in a single pass). They also vary by format size, ranging from standard letter/A4 units to large-format ledger/A3 production machines.