For the past 30 years the operating speed and component density of digital electronics has steadily increased, while the price of components has steadily decreased. Today, designers of consumer goods are incorporating digital electronics into more and more of their products. If these trends continue, as we expect they will, many everyday items will soon include some form of computer.
Although computers are becoming ever more common in appliances such as VCRs, microwave ovens, and personal digital assistants, they remain largely isolated from one another and from more powerful desktop and laptop machines. We believe that in the future many computers will provide more valuable services in combination than they can in isolation. Ideally, many kinds of specialized machines will work together via networks to let users access and control information, computation and their physical and electronic environments.
In the Computer Science Laboratory (CSL) at Xerox PARC we have established a number of research projects to explore this vision, which we call Ubiquitous Computing. This paper presents the results of the PARCTAB project, an experiment intended to clarify the design and application issues involved in constructing a mobile computing system within an office building. The PARCTAB system provides a useful testbed for some of the ideas of the Ubiquitous Computing philosophy, which is described briefly in the next section. The system is based on palm-sized wireless PARCTAB computers (known generically as ``tabs'') and an infrared communication system that links them to each other and to desktop computers through a local area network (LAN). Although technological and funding limitations forced us to make numerous compromises in designing the PARCTAB hardware, nevertheless the system, as described in Section 3, meets most of our design goals. Likewise the small size and low resolution of the PARCTAB displays requires an innovative user interface design to allow efficient text entry and option selection. Our solutions are presented in Section 4.
A community of about 41 people at Xerox PARC take part in the system's operation and in PARCTAB application development, which are covered in some detail in Sections 5 and 6. To date, we have developed and tested more than two dozen PARCTAB applications that allow users to access information on the network, to communicate through paging and e-mail, to collaborate on shared drawings and texts, and even to monitor and control office appliances. Descriptions of the various PARCTAB applications as well as data on users' experiences with them are given in Sections 7 and 8, respectively.
By designing, constructing, and evaluating a fully operational mobile computing system and developing applications that exploit its unique capabilities, we have gained some insight into the practical benefits and real-world problems of such systems. In the paper's final section, we collect these lessons and present some of the many intriguing ideas that the PARCTAB project has spawned for future work in Ubiquitous Computing.