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Today the principal dividing line between keyboards is not technology but touch—what typing actually feels like. A keyboard must be responsive to the touch of your fingers—when you press down, the keys actually have to go down. More than that, however, you must feel like you are typing. You need tactile feedback, sensing through your fingers when you have activated a key.

The most primitive form of tactile feedback is the hard stop—the key bottoms out and stops moving at the point of actuation. No matter how much harder you press, the key is unyielding, and that is the problem. To assure yourself that you are actuating the key, you end up pressing harder than necessary. The extra force tires you out more quickly.

One alternative is to make the key actuate before the end of key travel. Because the key is still moving when you realize that it registered your keystroke, you can release your finger pressure before the key bottoms out. You don't have to expend as much effort, and your fingers don't get as tired.

The linear travel or linear touch keyboard requires that you simply press harder to push a key down. In other words, the relationship between the displacement of the key and the pressure you must apply is linear throughout the travel of the key. The chief shortcoming of the linear touch keyboard is that your fingers have no sure way of knowing when they have pressed down far enough. Audible feedback, a click indicating that the key has been actuated, can help, as does the appearance onscreen of the character you typed. Both slow you down, however, because you are calling more of your mind into play to register a simple keystroke. If your fingers could sense the actuation of the keys themselves, your fingers could know when to stop reflexively.

Better keyboards provide this kind of tactile feedback by requiring you to increase pressure on the keyboard keys until they actuate and then dramatically lower the force you need to press down farther until you reach the limit of travel. Your fingers detect the change in effort as an over-center feel. Keyboards that provide this positive over-center feel are generally considered to be the best for quick touch-typing.

A spring mechanism, carefully tailored to abruptly yield upon actuation of each key, is the classic means of achieving a tactile feel and can be adapted to provide an audible "click" with every keypress. The spring mechanism also returns the key to the top of its travel at the end of each keystroke. The very first computer keyboards were elaborate constructions that used a separate spring assembly for each key. Modern keyboards use a single overall spring assembly or, more likely, an elastic rubber dome that pops between positions. Dome-based keyboards give satisfying tactile feedback, but individual keys may sporadically require increased force for a stroke or two, thus subverting their smooth operation. Nevertheless, the low cost and good reliability make dome technology popular among keyboard-makers.

Soft-touch keyboards use a compressible foam to work as the spring mechanism as well as to cushion the end of each keystroke. Soft-touch keyboards give a more linear feel but are preferred by some people for exactly the same reason others dislike them—their lack of snap and quiet operation.

Another influence on the feel of a keyboard is the force required to actuate a key. Some keyboards require you to press harder than others. In general, however, most keyboards require between 1.9 and 2.4 ounces of pressure to actuate the key. Stiff keyboards can require as much as three ounces.

On March 22, 1999, Key Tronic Corporation introduced the first varied key-feel keyboard, one that required differing amounts of pressure to activate its keys. Called ErgoForce by its developer, the varied key pressures are tailored to the fingers expected to activate them. For example, the "A" key, which is usually operated by the left little finger, requires only 1.25 ounces (35 grams) of force to activate, whereas the spacebar requires 2.3 ounces (80 grams). Depending on the location of each key, it requires one of five levels of effort to activate—35, 45, 55, 65, or 80 grams. According to the manufacturer, the tailored effort makes typing easier and improves the level of typing comfort for people using a keyboard for long periods.

Keyboards also differ in how far you must press down on a key to actuate it. Full-travel keyboards require your fingers to move down between 0.14 and 0.18 of an inch to actuate a key. Studies show that the full-travel design helps typists achieve high speeds and lower error rates. In laptop and notebook computers, where every fraction of an inch counts, however, keyboards sometimes are designed with less than full travel. A short-travel keyboard actuates with less than about 0.10 inch of key travel. Whether you can live with—or even prefer—a short-travel keyboard is a personal issue.

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