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I've just noticed a strange behavior of my keyboard.

First, I tried holding A, which created a bunch of aaaaa.

Then I held D, which created aaaaaddddd.

However, when I pressed Z, the key pressing was not detected.

The stranger thing is that when I tested the finding with the D, G, and C combination, it did produce the ccccc.

Furthermore, two separate keys A & Z, or D & Z still work.

I've also found that the last key is only received when the first two keys are among the middle keys of the rows, i.e. D to K, or E to I.

The numpad keys also suffer from this behavior.

This problem is found on all the keyboards I've tested so far (which are all connected to Windows PCs/Laptops). Yet I'm not sure if it's universal on every keyboards. Do you have any explanation to this strange behavior?

Uahnbu Tran
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1 Answers1

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Keyboard ghosting is when a keyboard doesn’t register a key being pressed, even though the user has pressed it correctly. This feature was used principally by Windows in the famous Ctrl-Alt-Delete.

Most keyboards today can support up to three ghosted keys, but this may differ between keyboards. For such keyboards, three key-presses will be recognized, but following keys will be ignored. However, the architecture of the internal electrical circuits will determine how well this will work for any given three keys.

You may find "anti-ghosting" keyboards, which will typically list the number of supported keys, such as "25-key anti-ghosting". This won’t cover the entire keyboard for anti-ghosting, but will rather target individual keys that the manufacturer considers tend to be held down together.

There exist also n-key rollover keyboards that have no upper key limit, meaning no ghosting at all.

harrymc
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