Abstract: "The Wearable Computer Project is a testbed integrating research on rapid design and prototyping. Based on representative examples from six generations of wearable computers, the paper focuses on the differences in rapid prototyping using custom design versus off-the-shelf components. The attributes characterizing these two design styles are defined and illustrated by experimental measurements. The off-the-shelf approach required ten times the overhead, 30% more cost, fifty times the storage resources, 20% more effort, five times more power, but 30% less effort to port software than the embedded approach."