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Why do Macs ask you to press random keys when connecting a new keyboard?

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Why This Matters

This article explains why macOS prompts users to press specific keys when connecting new keyboards, highlighting the importance of correctly identifying keyboard layouts to ensure proper key mapping. The process helps accommodate various international layouts, but can be primitive and sometimes inaccurate, especially with non-typing peripherals. Understanding this mechanism is crucial for both developers and consumers to avoid input errors and improve user experience.

Key Takeaways

You might have seen this, one of the strangest and most primitive experiences in macOS, where you’re asked to press keys next to left Shift and right Shift, whatever they might be.

Perhaps I can explain.

There are three main international keyboard layout variants in common use: American (ANSI, with a horizontal Enter), European (ISO, with a vertical Enter), and Japanese (JIS, with a square-ish Enter).

The shape of Enter and the shuffling of the surrounding keys is not the only difference. It’s also that the European layout has historically always had one more key – shoved in between Shift and Z – and the Japanese layout a few more.

But the main challenge is that a keyboard doesn’t have a way to tell the host computer what are its exact keys and where they’re located.

So, pressing the thing next to the left Shift can help Apple understand whether the keyboard is American or Japanese (always Z) or European (something else, but never Z). And pressing the thing next to the right Shift differentiates JIS (where it’s the _ key) from another keyboard (always /).

What I called “primitive” just above is actually clever in its approach. The legend of the key next to left Shift varies per locale (you can compare here), so the system can’t just tell you to press the < > key – and besides, asking the user to find a key that might not exist is a lot more stressful. And, identifying the keyboard by choosing a layout visually wouldn’t work either, since there are a million of layout variations – imagine having a split or a compact keyboard!

But it still is primitive, because it will still open up even if the keyboard you connect isn’t really a typing keyboard…

…or even if it doesn’t have any keys at all. (Some peripherals like credit card readers and two-factor dongles identify as keyboards as they transfer information by sending keystrokes.)

But: Why does it matter? What happens if you select the wrong layout or ignore the dialog?

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