The secret of the tera-keyboard


Many characters in Ghost in the Shell have a particular cybernetic augmentation that lets them use specially-designed keyboards for input.


To control this input device, the user’s hands are replaced with cybernetic ones. Normally they look and behave like normal human hands. But when needed, the fingers of these each split into three separate mini-fingers, which can move independently. These 30 spidery fingerlets triple the number of digits at play, dancing across the keyboard at a blinding 24 positions per second.


The tera-keyboard

The keyboards for which these hands were built have eight rows. The five rows nearest the user have single symbols. (QWERTY English?) Three rows farthest from the user have keys labeled with individual words. Six other keys at the top right are unlabeled. Each key glows cyan when pressed and is flush with the board itself. In this sense it works more like a touch panel than a keyboard. The board has around 100 keys in total.


What’s nifty about the keyboard itself is not the number of keys. Modern keyboards have about that many. What’s nifty is that you can see these keyboards are massively chorded, with screen captures from the film showing nine keys being pressed at once.


Let’s compare. (And here I owe a great mathematical debt of thanks to Nate Clinton for his mastery of combinatorics.) The keyboard I’m typing this blog post on has 104 keys, and can handle five keys being pressed at once, i.e, a base key like “S” and up to four modifier keys: shift, control, option, and command. If you do the math, this allows for 1600 different keypresses. That’s quite a large range of momentary inputs.

But on the tera-keyboard you’re able to press nine keys at once, and more importantly, it looks like any key can be chorded with any other key. If we’re conservative in the interpretation and presume that 9 keys must be pressed at once—leaving 6 fingerlets free to move into position for the next bit of input—that still adds up to a possible 2,747,472,247,520 possible keypresses (≈2.7 trillion). That’s about nine orders of magnitude more than our measley 1600. At 24 keypresses per second, that’s a data rate of 6.5939334e+13 per second.


So, ok, yes, fast, but it only raises the question:

What exactly is being input?

It’s certainly more than just characters. Unicode‘s 110,000 characters is a fraction of a fraction of this amount of data, and it covers most of the world’s scripts.

Is it words? Steven Pinker in his book The Language Instinct cites sources estimating the number of words in an educated person’s vocabulary is around 60,000. This excludes proper names, numbers, foreign words, any scientific terms, and acronyms, so it’s pretty conservative. Even if we double it, we’re still around the number of characters in Unicode. So even if the keyboard had one keypress for every word the user could possibly know and be thinking at any particular moment, the typist would only be using a fragment of its capacity.


The only thing that nears this level of data on a human scale is the human brain. With a common estimate of 100 billion neurons, the keyboard could be expressing the state of it’s users brain, 24 times a second, distinguishing between 10 different states of each neuron.

This also bypasses one of the concerns of introducing an input mechanism like this that requires active manipulation: The human brain doesn’t have the mechanisms to manage 30 digits and 9-key-chording at this rate. To get it to where it could manage this kind of task would need fairly massive rewiring of the brain of the user. (And if you could do that, why bother with the computer?)

But if it’s a passive device, simply taking “pictures” of the brain and sharing those pictures with the computer, it doesn’t require that the human be reengineered, just re-equipped. It requires a very smart computer system able to cope with and respond to that kind of input, but we see that exact kind of artificial intelligence elsewhere in the film.

The “secret”

Because of the form factor of hands and keyboard, it looks like a manual input device. But looking at the data throughput, the evidence suggests that it’s actually a brain interface, meant to keep the computer up to date with whatever the user is thinking at that exact moment and responding appropriately. For all the futurism seen in this film, this is perhaps the most futuristic, and perhaps the most surprising.


9 thoughts on “The secret of the tera-keyboard

  1. I would argue that it’s a substitute for the high-bandwidth 4-pin direct brain connection that is used fairly consistently for brain-computer I/O. There are a couple of ways that the chorded keyboard might be superior than a direct brain connection:

    – Interoperability, since the 4-pin connection might not be a universal standard, especially since the example cited above is an American official interfacing with a Japanese computer, and
    – Security, as using the keyboard is a method of unidirectional communication, whereas the direct connection has shown itself to be susceptible to hacking.

    So if one were interfacing with an unknown and untrusted computer terminal but wanted to keep up with the bandwidth of a direct connection, this keyboard would be an ideal compromise. I don’t think that “thinking fast enough” would be an impediment, since everyone in GiTS has a cyberbrain implant (even Togusa, who was “all natural” otherwise) that should help.

  2. So you’re saying that this keyboard allows as many combinations as the brain would have if each neuron had 10 different states. This presumes that all those states have been mapped and are known to the user and to the system.
    Given the diversity of the brains, the development of this communication protocol is in itself preety amazing. But it might be limited, for instance … is 10 states enough? Is it only states of the neurons what matter?
    I mean, we don’t know, science has not figured that out yet.

    Also, why would the computer need to know the entire state of your brain?
    I’m thinking that, even if the protocol allows for the entire current state, the user can chose what part of that state to reveal. This is useful, as said in the prior comment, for security reasons, you don’t want to reveal all you’re thinking of. But even more important is the hability to direct the computer to solve the one issue you want to solve right now, if you give it the full contents of your consciousness the computer might get confused and start solving a different problem that is not the one you intended, that why it might be good to only reveal part of your brain’s status all the time.

    • I’m really just noting that it’s the closest thing we have that might be represented by the implied data rate. There’s lots of questions around this conjecture of course.

      I agree that a selective disclosure is more desirable. Maybe that’s the power of the mechahands, in that it only expresses conscious thought.

  3. Pingback: Report Card: Ghost in the Shell | Make It So

  4. Coming late to the game here, but i think it’s important to note the differences between written Japanese and say, English. (Note: i’m not including the totals in unicode in this example, too lazy to look them up.)

    English has only 26 letters, 10 Arabic numbers, the variety of punctuation marks, plus the other functions typically mapped onto a keyboard, which gets arranged into a small number of keyboard layouts (the 104-key QWERTY being the current norm for most users).

    Japanese, on the other hand, has 2 seperate syllabaries (each consisting of 113 characters), up to 85 000 Kanji characters (of which only 2 000 to 3 000 are considered to be in “common” use, but at least 13 000 of which are coded for in industrial standards for Kanji), 10 Arabic numbers (when used instead of the native Kanji), the native and imported punctuation marks, plus the same other functions typically mapped on to keyboards, which then gets mapped onto either a keyboard printed in English characters (requiring knowledge of how to get the exact characters desired) or with Hiragana and English characters.

    (Note: i have no experience with either keyboard, so i’m not sure how well that they work beyond the known limitation of the Shift-JIS standard to something well below the total number of possible characters, a bit over 6000, if i recall correctly).

    So as far as the hand-splitting and funky keyboard go, would it not then be reasonable to think that perhaps this is merely a method for actually getting all the possible combinations in there? Especially when considering that it could be labelled with the 252 radicals (parts of individual Kanji which combine into whole Kanji) plus katakana, hiragana, some arabic numerals, etc. In which case, 9 keys pressed at once could be necessary for typing a single Kanji?

    (Sources: and wwwJDIC)

  5. While your conjecture is possible, it sounds to me more like it is an easy way of manually transferring a compressed file. You type the compression dictionary at the start, then hit the combination of keys that matches the compression key you transfer next. That way you could transfer a file, say a program, virus, etc, much more quickly onto an airgapped computer then you could retype and compile the source code.

  6. Okay, so I just happened to randomly come across this post. The math is completely off the rails – the fact that there are 2.7 trillion possible chord combinations of 9 keys does not mean you enter 2.7 trillion things every time you type a chord. You type a single chord out of 2.7 trillion possibilities, meaning you convey about 42 BITS of information (bits, not even bytes) with each chord – 2^42 is about 4.4 trillion possible combinations. If you type 24 chords per second, you are conveying about a thousand bits or 125 bytes to the computer per second. That’s a speed of information transfer comparable to a 1970’s-era modem. There’s no brain transfers going on here, just 1500-WPM typing.

    • You know when I wrote this all those years ago, I checked in with a math nerd friend, and worked with his figures. But it was beyond my ability to refute, as is this.

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