The IBM 3800 Printing Subsystem is controlled by a high speed multilevel, interrupt-driven microprocessor. The design of this system has included several innovative concepts to take advantage of the flexibility of electrophotographic laser printing. New functions that are introduced include intermixed pitches, fonts, and line spacings; user-alterable character sets; on-line forms generation; and superior retry, fail-soft and diagnostic capabilities. Compatibility with the operational characteristics of IBM 1403 and 3211 printers is maintained. This paper discusses many of the objectives, development tradeoffs, and resultant control implementations for an on-line computer output printing subsystem.