The report describes the Classroom Information and Computing Service (CLICS), a pedagogical computer-based information system that is used as a case study in the subject "Information Systems" in the Dept. of Electrical Engineering at M.I.T. CLICS is an abstraction of the Multiplexed Information and Computing Service (MULTICS) that is being implemented by Project MAC at M.I.T. As such, it is an example of computer utility. CLICS is derived from MULTICS by a combination of simplifying the mechanisms of MULTICS and removing some of its more exotic features; and embodies research into ways to simplify the mechanisms of MULTICS without sacrificing service objectives. The report is a specification of the hardware, control programs, and system implementation language of the CLICS system, as developed to date. The system is specified in sufficient detail for students to develop a structural as well as a functional understanding of its operation and mechanisms. As the primary case study for an undergraduate subject, CLICS provides specific examples of the complexities in a general purpose information system, and methods of coping with them. (Author)