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From Citizendium, the Citizens' Compendium
A Wearable computer is a computer that is inside the personal space of the user, is always on and always accessible. The device is always with the user, and it can be used while doing other activities. A wearable computer is more than just a wristwatch or regular eyeglasses: it has the full functionality of a computer system, but in addition to being a fully featured computer, it is also inextricably intertwined with the wearer.
There are three new ways how a wearable computer and it's user may interact.
- Constancy: The computer is supposed to be always on when it might be needed. Unlike a cellphone, wrist-worn computer, or notebook, a wearable computer does not need to be opened up and turned on to be used. The computer and user may constantly interact with each other.
- Augmentation: Traditionally when we use computers, we do it as a primary task. The assumption of wearable computing is that the user may concentrate his mind on the primary task while doing the computing as secondary task. A wearable computer is supposed to aid, or augment our intellect, or senses to give the user more resources for the task at hand.
- Mediation: Unlike any other computing device, the wearable computer can usefully enclose some of our senses. For example it can block out material we might not wish to experience, like offensive advertising. It allows us to alter our perception of reality somewhat, by modifying the information we see, before our senses have a say in it.
Depending on how broadly one defines a wearable computer, as some define it a lot more broadly than in this article, a wearable computer goes as far back as 1961, where Ed Thorp and Claude Shannon invented a small computer they used to predict roulette wheels, and the computer was hidden under the user's clothes. The first important to-be parts of most wearable computer systems were also invented in the sixties, when the first head mounted display and chording keyboard were built.
The first "modern" wearable computer was built by Steve Mann in 1981. He wired a computer in his backpack, hacked a camera viewfinder to a helmet, and used some microswitches for input. The rig was used for controlling photographic equipment, as he was a hobbyist in that field.
Steve Mann continued to improve the design and built several other rigs. He tried several different things, like belly-mounted-display, and he noticed that the wearable computer can be used for most things you can use a desktop computer for. His latest wearable computer related works you can read on the Internet are underwear-worn computer, which is completely hidden from view, only a chording keyboard on his belt and a colorful wire going to his sunglasses might notify the clueless bypasser about something weird going on. He is also the inventor of Eyetap system, which is basically a HMD, which cleverly uses a camera and a display so that the computer may modify the picture the user sees, before it reaches the eye of the user.
Newest things in wearable computing is the Sixth Sense project from MIT, which is now open source. It has a camera recording your hand gestures, and a small projector, which is the display.
Advantages and Limitations
- Freedom from desk. A wearable computer is preferably wireless, so that there is no wires going from user to anything. Of course it might have ethernet connection or similar, but it should not depend on external devices.
- Always connected to the Internet and/or reference materials.
- Notes, to-do lists and stuff always with you.
- Immediately usable. No need to get it from bag or pocket and/or turn it on.
- It's a full PC. While you might not want to use it for video-editing, you can use plenty of external devices for it. Also, there is already lots of software for it.
- Currently (2010) the commercial wearable displays are suboptimal.
- To get most from it, you need to learn to use a chording keyboard, which takes a while.
- Might not be socially acceptable. Especially the display.
- May be hard to use outside in winter.
- Carrying a wearable is a bit hard. Usually people seem to have it in a bag, some newer are worn with a strap from shoulder to waist. Both have advantages and disadvantages though.
Notable users and rigs
- Steve Mann, Wearcomp 1-7
- Greg Priest-Dorman, Herbert, Herbeee 
Central Processing Unit
Many wearable main units are made from PC/104 -boards. Some rigs use the Beagleboard.
Most used output system for a computer is the display, and a wearable is no different in that sense. Usually wearable computers use head mounted displays, though some use only audio based output.
Most wearable computer users prefer to use some kind of chording keyboard. It often looks like a remote control, and it usually has 5-8 keys. The characters are produced by piano-like chords, where multiple keys pressed and released will make a character. Twiddler 2 is the best known chording keyboard, though it is not produced any more. Spiffchorder is an open source chording keyboard, which is cheap and pretty easy to build if one knows any electronics.
In 1665 Robert Hooke wrote about the possibility of man getting augmented senses via technology. He noted that as eyeglasses had improved seeing, it would not be improbable that other senses could augment, that is empower our hearing, smelling, tasting and touching. That is something wearable computers are already doing for their users, they can see in the dark, they may have zoom and face recognition and microscope. They can have haptic radar senses, they can have eyes on their back and they can, and have already successfully augmented their senses in many other ways.