A recent trend in computing is for more capability to be packed into smaller spaces with less power consumption. At first this trend was pushed by laptop computers. With the advent of pen computing and PDA's, components have become even smaller and more manageable. Now it is possible to make a computer which can be worn and run constantly [Starner et al, 1995].
For example, the author's wearable computer requires 5 W of
power to run all components continuously (head mounted display, hard
disk, 25 MHz 80386 CPU, 8M RAM, serial/parallel/PCMCIA ports, etc.)
A standard off-the-shelf 1 kg gel cell battery can provide this unit
power for 6 hours. However, such a battery has a volume of 450 cm
.
Better battery technology is available, and the author's computer does
not use power management.
A viable wearable computer could be made with a PIC12C508
processor from Microchip Technology Inc., requires only 10 mW at 4 MHz
and 60 
W at 32 kHz [PIC data sheet]. With memory instead of rotary disk
storage, some driver circuitry, and a Private Eye
head mounted display
from Reflection Technology Inc., a functional wearable computer (without
communications) could be made with a power consumption of 0.5 W. Thus,
significant computing power can be obtained even on a relatively
strict power budget.