Inside IBM's Model M Keyboard
IBM's Model 5150 PC, released in 1981, was a classic, perhaps the computer most responsible for launching the PC revolution. (In fact, it's one of our 25 Greatest PCs of All Time.) Sadly, however, its keyboard did not live up to that standard. This 83-key model was IBM's first, and critics hated it, complaining about its awkward layout and nonstandard design. Stung by the criticism, IBM assembled a ten-person task force to craft a new keyboard, according to David Bradley, a member of that task force and of the 5150's design team. Their resulting 101-key design, 1984's Model M, became the undisputed bellwether for the computer industry, with a layout that dominates desktops to this day. As we peek under the hood of this legend, you'll soon see why many consider the Model M to be the greatest keyboard of all time.
Meet the Model M
This is my keyboard. It's just a few months shy of 22 years old, and I use it every day.
The first thing that may strike you about the Model M is the layout: It's so normal. There's no pesky "Windows" key here; nor are there buttons to turn your computer off, play a CD, or start your car. Just the basics, as IBM defined them 24 years ago. Some would say its only flaw is the prominent placement of the Caps Lock key (in lieu of "control" on earlier keyboards). But it's a minor error compared with the modern keyboard's multitude of sins.
Beneath the Keycaps
When designing the Model M, IBM engineers thought ahead. Almost every key on the keyboard has an easily removable keycap that allowed the user--or IBM--to easily change the layout or color of the keyboard. This was especially important for IBM's international keyboard releases, which incorporated subtle layout differences from the U.S. version. The keycaps are also durable; the label on each key is molded into the plastic itself, ensuring that it wouldn't wear off with use.
As with the keycaps, the Model M's cable design supports modular extensibility. One 6-pin port on the back of the keyboard (left) allows for a number of configurations, from the traditional 5-pin AT connector seen here (right), to the PS/2 connector, and various IBM terminal connectors. Any compatible connector upgrade is only a new cable away.
The Flip Side
The Model M provides two sturdy, retractable feet on the base of the unit to change the operational angle of the keyboard. The speaker grille you see here is a holdover from an earlier terminal keyboard mold that was used with the Model M--the M contains no speaker.
22 Years of Service
As you can see by this label, IBM manufactured my Model M on August 13th, 1986. That's almost 22 years ago, and the keyboard still gets daily use (I even wrote this article with it). It still feels and sounds just as good as any newer Model M I've used--a powerful testament to its durability and relevance. Stop for a second and consider how many 22-year-old computer parts you still use on a daily basis. Exactly.
Under the Hood
Every keyboard hides a dirty secret: a years-long accumulation of dust, dirt, hairs, crumbs, and whatever else fell between the key cracks. But after splitting open the case, I was surprised at how clean my Model M was, especially when compared with a particularly nasty Apple II+ keyboard that I cleaned off recently. The Model M's design ensures smooth operation even when dirty (we'll talk more about that shortly, or go to slide 9).
They call IBM keyboards "clicky" for a reason: With every keystroke, the keys produce a satisfying click-thunk-click via a patented mechanism called the "buckling-spring actuator." Every key press compresses the key spring until it suddenly snaps against the side of a black plastic cylinder (seen here), producing the "click" sound. Meanwhile, the spring, thus compressed, pushes a tiny pivoting rocker beneath each key that registers the key press on a membrane below.
A Durable Design
The Model M owes its incredible life span not only to its buckling-spring design, but also to the fact that each plastic key covers the only hole leading to the switch below, which in turn is covered by a rubber membrane, making it very hard for dust, dirt, or even liquid to reach the operational core of the keyboard. But cleaning an M is easy. Even under the force of a powerful vacuum cleaner, the small springs you see here don't budge--they're thankfully attached to elements beneath each key.
Built Like a Tank
The Model M is a hefty piece of hardware. Fully assembled, my unit weighs over 5 pounds. A large portion of that weight comes from the solid steel back plate on the bottom of the keyboard assembly (seen here removed from its plastic chassis and flipped over). The weight afforded by the steel is nice; it prevents the unit from sliding around while you're typing. If necessary, the Model M can also function as a battering ram or makeshift ballistic shield.
Also, that's the M's controller board sitting atop the base. You'll see the other side of the controller on the next slide.
The Man Behind the Curtain
Within every Model M is a tiny computer--a Hitachi 6805 microprocessor--that encodes key presses and interfaces with your PC. This board connects to the keyboard assembly via two thin plastic ribbon cables (not pictured), while the big black connector to the upper left receives the 6-pin external keyboard cable we talked about earlier. The white 4-pin connector to the right powers the Num Lock, Caps Lock, and Scroll Lock indicator LEDs, and the braided cable to the far left is a grounding wire.
Another important component of the Model M's durability is its thick, rugged plastic shell, seen here devoid of any contents. It'll take a sizable beating without cracking, and it won't fly away in a breeze, even when empty. When you put all its components together, the Model M is a formidable keyboard that will serve a user reliably for years.
A Pale Imitation
Let's take a look at the Model M's competition. Here we have a modern, generic, $1-bill-of-materials, Chinese-made keyboard, the kind they toss out as confetti during parades and give away with PC clones as mere afterthoughts in a mouse-centric world. Compared with the tanklike Model M, this fragile, 1.5-pound keyboard is a lightweight (you could easily break it over your knee). Like most modern keyboards, it includes several extraneous keys and buttons that either annoy the seasoned typist or threaten your computer's stability because of the drivers required to make them work.
The No-Click Solution
Unlike the Model M, this keyboard's keys snap into place over silicone-rubber dome switches. The keyboard is very quiet, which can be a plus in certain environments, but it won't last nearly as long as keyboards built on the buckling-spring design. Dome-switch keyboards are also much less expensive to produce than keyboards with more complicated mechanical switches, which is why they dominate the keyboard market today.
Here's a look inside a typical modern keyboard. Beneath each key lies a free-floating silicone dome switch that can easily wear out over time or degrade in harsh environments. When depressed, the dome buckles and pushes together two contact-laden plastic membranes, completing the circuit and registering a key press.
For many users, a keyboard like this is probably good enough. After all, if it wears out, it's cheap to replace. But for serious typists, or those who simply appreciate a solid keyboard beneath their fingers, an IBM Model M is, without question, the only way to go.