The use of microcomputers with online catalogs is a partnership that is gaining wide acceptance and leading to dramatic changes in how we think about online catalogs. There are two major ways in which microcomputers are used in an online catalog system: (1) the microcomputer provides all the computer support for the entire system, i.e., the microcomputer is the system; (2) the microcomputer is a replacement for the conventional or dumb terminal. This use of microcomputers changes significantly the architecture of online catalog systems. For the fist time, library patrons may be linked directly to the online catalog without an intermediary. The intelligence and data storage of the system may be distributed to the most efficient and/or cost effective location. The programmability of the microcomputer makes it suitable for supporting new user-system interactions such as electronic bulletin boards, electronic mail, and various store-and-forward operations. Finally, the partnership of the microcomputer with telecommunications truly brings the world of information directly to the library user. For the first time ever, the "library without walls" is a reality. (MES)