The computational requirements of mobile machines

For the last few years mobile (or nomadic) computing has generated tremendous interest in both the research and the industrial community. Mobility is seen as an area of great potential benefits, both in terms of products and research contributions, However, at this time, mobile systems are so novel that there is little practical experience regarding their use. This has led to much speculation regarding a number of system issues such as determining what the killer apps will be, the hardware architecture of the nomadic machines, deciding whether communication or computation will be their primary feature and so on. One of the issues yet to be resolved is that of the architecture of these machines. Will mobile machines be essentially a new type of portable computer (although perhaps smaller, less powerful, friendlier, and pencentric) or will we carry around with us the equivalent of an X-window terminal (i.e., simply a display device, with all computation being carried out at a non-mobile server)? Examples of the first approach are the Apple Newton and the EO computers formerly marketed by AT&T, while the second approach is being explored by a number of other researchers (e.g., the InfoPad project at U.C. Berkeley, or the Xerox PARC tabs). This paper briefly describes the research issues involved and outlines the pros and cons of either approach. We also explore in detail one particular aspect, namely, the performance implications of the choice of architecture in a distributed information system. The results are presented as a set of simulation-based studies