In June of 2012, Microsoft announced the first devices in its new Surface line, twin tablets to take on the ascendant iPad while simultaneously challenging the idea of what a tablet could be. And as part of that reveal, it also introduced two new but very different kinds of keyboards.

The Touch Cover was less than 3 millimeters thick and covered not in keys, but in almost imperceptible key-like bumps. It was a radical and uncanny attempt to transform the keyboard, to reconsider its most basic elements. It flopped.

The Type Cover, meanwhile, was a simple shrink job, but an impressive one. Here, Microsoft squeezed your average laptop keyboard into an ever smaller package, one slim enough to function as a rigid but still normal-looking tablet cover, offering a typing experience much better than tapping on a touchscreen. Today the Touch Cover is no more, but the Type Cover, now in its fourth iteration, is easily one of the best thinnest keyboards you can find.

The story of these two weirdo twins tells us a lot about how we interact with a keyboard, what makes a modern keyboard work, and what separates a good keyboard from a bad one. The Touch Cover had been sterile and lifeless from the start, from the moment Microsoft built a "board" without the "key." But the Type Cover survived and improved.

you know a bad keyboard as soon as you type a sentence on it.

Maybe you've never thought about what makes a great keyboard, but you know a bad one as soon as you type a sentence on it. The keys are mushier than cold oatmeal. They quiver under the lightest touch as you drown in a sea of your own typos. The board is cramped. It makes you feel like you're typing with mittens on. There's no click, no bounce, no… what do you call it, anyway?

I talked to Rob Bingham, senior hardware program manager for Microsoft and steward of the Type Cover project, about the subtle, under-appreciated qualities that separate the good from the bad, and the great from the good. "It's not like you see '50 percent less squishy' or 'New, improved clickiness' in big bright letters on the outside of product packaging," he says. "You grab a specific configuration, type on it, and you just know, 'It's the one.'"

That gut feeling may be good enough for you are me, but when you're designing one of the things, you need hard data on what makes a keyboard better. And so there's a small but important vocabulary has sprung up to turn subjective feelings into quantifiable attributes manufacturers can observe, talk about, and—most importantly—control. From there, you can boil down a good keyboard to three main elements, according to Bingham: The travel, the snap, and the discoverability.

The Travel

The travel, sometimes called the throw, is most simply described as "how far the keys go down." With respect to their ancestors, the keyboards of modern laptops have comparatively little throw—they don't go down that far when you push them. Compare that to the days of the earliest typewriters, in the 1860s, when the sensation of typing a letter was more like driving that key down all the way through your desk and 30 miles into the Earth's crust. The mechanics of these early machines differed, but the cause-and-effect relationship was simple: Key goes down, lever goes THWACK. Bam, you just typed an M

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Electric keyboards tackled the problem of completing a circuit in all sorts of different (but still vertically intensive) ways. The earliest versions used spring-loaded keys to drive pins through holes to complete a circuit lurking below the keys. Elsewhere, other clever implementations, like IBM's "buckling spring keyboard," pursued stranger, more unique solutions, like springs that complete a circuit by touching metal to the side of them.

These sorts of mechanisms still exist today, inside the special—and often expensive—enthusiast keyboards we all generally refer to as "mechanical keyboards." The term technically applies to any keyboard with moving parts as opposed to touchscreen keyboards or other typing surfaces that literally don't move at all. But when it comes general usage, it typically refers to keyboards with keys that use rigid components made of metal and plastic to complete circuits in a way that gives them a distinct feel and a deep throw—the sort of vintage click-clack keyboards typing nerds, PC gamers, and other tactile enthusiasts still lust after.

But for the most part, keyboard tech has moved on to thinner fare. Keys with deep throw may add an oddly satisfying acoustic and tactile experience to the typing process, but cramming a mechanical keyboard into a laptop turns it into impractical and hulking beast . To slim down, laptops keyboards, Bluetooth keyboards, and even some desktop keyboards (Apple's, for instance) have moved on to mechanisms and switches based on rubber and plastic. Inside of one of these keyboards, underneath the keys, you'll find a single sheet of some pliable material with a bunch of little domes.

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When you hit the keys, the domes go down. This is the switch that makes the keys go. Each of these keys are usually surrounded by a framework of plastic—more on that in a second—but it's the collapsing membrane that does the job of connecting a circuit. That setup carries with it several advantages. These membranes are cheap and durable. They can be waterproofed. And they can fit inside very thin bodies.

Of course, you need to be careful not to go too thin. Apple's newest Macbook, for instance, is notorious for its lack of key travel. While most people agree the keyboard is useable once you get used to it, people tend to find it unpleasant.Wired calls it a cross between a keyboard and tapping on glass , saying "suddenly I understand what typewriter aficionados are always droning on about: There's something wonderful about hitting a key and having something happen." Or as Gizmodo puts it: "I feel like I'm stabbing my fingers into a hard surface. I feel the impact in my bones."

How do you deliver a satisfying THUNK without making the keyboard thicker?

We've arrived at the design problem that vexes keyboard-makers: How do you delivery a satisfying THUNK without making the keyboard thicker? One solution is to excavate new space inside the shell you already have. "Every generation, we look at the mechanism under the keycap itself and find ways to make the same linkage assembly occupy less and less space," Bingham says. "We're routinely designing with clearances in the tenths of millimeter to squeeze out every last bit of thickness."

And every last bit counts. Compared to traditional mechanical keyboards, which can have a travel distance of some 4 millimeters from top to bottom, laptop keyboards often move two millimeters or less, a far shorter distance than their forebears. But by making use of every hair-breadth of otherwise-wasted space, modern membrane keyboards can actually increase their precious travel distance while still getting thinner on the whole.

The Snap

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But travel isn't everything. In fact, keyboard designers have learned that they can (almost) fake the feeling of throw by tweaking the second crucial quality of the keyboard: the split-second when it clicks, and how much force it takes to do it. It's what Bingham calls the snap ratio.

Also referred to as "force-to-fire," the snap ratio is the amount of force you must apply to the key before it will move all the way down and type a letter. Try it right now. Press a key slowly and feel out its inertia before it suddenly gives way. A good snap ratio means you'll have to amp up the pressure a bit before the key gives up and goes down.

Press a key slowly and feel out its inertia before it suddenly gives way.

A keyboard can accomplish this sensation through the use of a few different mechanisms, most of which take the form of a collapsing plastic framework that sits around the membrane's rubber dome. The most common is a "scissor switch," which takes the form of two x-shaped braces that hoist the top of the key over the top of the rubber dome that it compresses. Throw a couple of springs in there, and you can generate resistance so that pressing down on the keys feels springier and snappier than just mushing your finger down on some rubber dome.

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This sensation isn't exactly a click like the kind you'll find in mechanical keyboards. Those taller keys will sometimes have two rigid pieces that will actually smack into each other on the way down to make a click, or other circuit-completing components that click by necessity. Shorter travel keys don't have that luxury so instead, that build-up and sudden drop-off of a tight snap ratio is a membrane's best chance to offer a sensation that's roughly analogous.

A good snap connects the appearance of a character on screen with a KA-CHUNK moment, just like the keyboards of old.

"The snap ratio is very important," Bingham says, "so you push on the key, you get resistance and it breaks away at the right place." A good snap connects the appearance of a character on screen with a KA-CHUNK moment, just like the keyboards of old. Without it, each stroke is just a soft, frustrating motion with the character appearing onscreen at some arbitrary point in the process. That snap is what gives a modern keyboard its click, and that's absolutely crucial.

The Discoverability

The third important feature of your keyboard—and one that's rarely discussed in detail, and is nearly impossible to notice unless it's absolutely abysmal—isn't about how the keys click. It's about how easy it is for your fingers to find their way to the right keys without getting lost on the way. That's discoverability.

Laying down a baseline is easy enough; just put the keys in the right places. We're all familiar with our standard QWERTY layout and it rarely, if ever, differs from keyboard to keyboard. But even when all the keys mapped to the places you're used to finding them, subtler details of their layout and design can be crucial. "There are a couple of ways to improve the typing performance and discoverability of the keys," Bingham says. "Like pitch and dish."

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Pitch is just the distance between the centers of each key, a measure of whether a keyboard feels roomy or cramped that's relatively independent from a keyboard's actual, physical size. On most full-sized keyboards, there's a pitch of about 18 or 19mm from the middle of one key to the middle of the next. After years of typing on keyboards that adhere roughly to that standard, that distance winds up ingrained in your muscle memory.

So even when trusty QWERTY ensures the keys are in their regular spots relative to each other, wonky pitch can throw them off relative to where your unconscious mind expects your fingers to be able to find them. Make it much smaller than that (like on the tiniest Bluetooth and tablet keyboards) and suddenly you're you're typing p's instead of o's and end up ;p;p;p;p;-ing when you meant to lololol.

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Dish, meanwhile, is that subtle bit of concavity you'll sometimes spot on a key's top. A keyboard key is not a perfectly level box; It's really more like "bowl," with the inward-curving sides guiding your fingers towards the center. But there's another way to subtly drag your fingers to the center of the right keys: shrinking them down. "It seems counter-intuitive," Bingham says, "but you can also make the keys smaller and put more spacing around them. It gets you in the center of the key and your accuracy and your typing performance goes up." That's the thought process behind "chiclet" keys, those squarish island keys with canals of negative space in between them.

Once used as shorthand for "ew, gross laptop keyboards," chiclet design has wormed its way onto just about every modern membrane keyboard worth its salt. Despite looking like more traditional mechanical keyboards (but flatter), non-chiclet designs offer none of the benefits of old-school designs while also introducing new problems by being so flat and cramped. Without enough height to come to a significant peak, these keys tend to just sort of run together.

That not only makes them harder to find, but it also compounds your typing errors. With virtually no space between keys, it's easy to lose track of whether you've got your finger over one key or the junction between like three of them and your typos are suddenly having baby typoes of their own. A single j becomes j, i, and k all at once and you get another grey hair.

But on a chiclet keyboard, the stark edges of the elevated keys provides a constant feel for where your fingers are in relation to the keys around them. So shrinking down the keys to exaggerate those gaps can actually make them easier, not harder, to hit.

These three factors—how far your fingers drop when they hit the keys, how much force it takes to make them go down, and how you know where your fingers are without staring at them like a hunt-and-peck typist—form the design foundation of virtually every keyboard you use on a regular basis. When it comes to the best ones, a lot of time and energy goes into tweaking each part. But you'll be forgiven if you've never really noticed before. That's exactly the point. If you don't think about your keyboard, that means its design is successful.

"The best keyboard is a keyboard you don't notice," Bingham says. Like a pen or pencil, a good keyboard is ultimately just an extension of you, more of an invisible interface than an object in and of itself. Of course, there's no accounting for taste. For some people, God types on a mechanical QWERTY and chiclet keys will always be the devil . But through a careful balance of past and present, modern laptop and tablet keyboards pay homage to the typewriters and keyboards that came before while exploring new frontiers in thinness and portability. The "good click"—that nebulous but all-important feeling—forms the through line that lets keyboard advance without feeling utterly alien.

That's vital, because while typing is not going away any time soon, keyboards will keep getting thinner. They must. The laptops on which they dwell will keep shrinking, and tablets toting tiny keyboards will keep fighting for their place. Meanwhile, we're all going to be typing more than ever. So while keyboards are need to keep getting smaller, but they still can't afford to be bad.

Yes, the keyboard could disappear eventually. There's a whole generation growing up with their thumbs glued to iPhones as we speak, as well as a whole slew of nascent technologies intent on blurring the line between touchscreen and tactile keyboard . But Bingham doubts that the touchscreen will kill the keyboard. "There's always gonna be this need to feel something move," he says. So far, at least, Microsoft's own experiments have proven that to be true.

The trusty keyboard types on.