A simple recorder made of reed with 6 finger holes is common in many cultures on several continents. Whether Indonesia, India, Africa or South America, there is always a kind of recorder that corresponds to the 6-hole pattern. These flutes only have 6 finger holes and no thumb hole (the well-known school recorder has 7 finger holes and one thumb hole).
With the 6 holes all notes of an octave can be played. If you then blow a little harder into the flute, it overblows and the higher notes of the second octave sound. Thus, these flutes can usually be played over two octaves.
In contrast to the standard recorder, which can also play the intermediate tones or semitones, this is only possible to a limited extent with the 6-hole recorder. You can grasp some semitones well, so that you can play both major and minor scales with a flute and also two or three different keys. For other keys, additional flutes are needed that are tuned to a different keynote. Therefore these flutes are available in many different tunings.
Even if the 6-hole flutes have been handed down for a long time, one variant made it into a celebrity at the beginning of modern times: the Irish tin whistle. With the beginning of industrialization, the popular small flutes made of sheet metal could be mass-produced and cheaply produced. So anyone could actually afford such a flute for a penny, hence the name “Pennywhistle”, which is why it was very popular. The tin whistle is known with its high notes from traditional Irish music, in lower variants also as low whistle.