Usually a question only our Sales Support Team knows the answer to.
For me to answer it, I had to look up the K-Number. Turns out it's the ALEXA Mini's GPIO Box.
What does it do?
The box offers a number of pin-outs for customized functions; so short-cutting one or the other can trigger a certain predefined function (configurable via the camera menu).
Where do I need it?
There are various use cases for GPIO. Imagine a shot where the camera is cramped in a tiny air-vent and the DP asks you to loose the ND. Because of all the metal in the air-vent the camera is perfectly shielded, so having a long cable with just some key function might come in handy.
Our friends at Gates use the GPIO box in their underwater housing and offer assignable buttons on the side:
John Ellerbrock elaborates their setup:
In our application, the GPIO box gives the underwater cameraman 12 user-assignable buttons that directly communicate with the Mini camera. The UW pro can access his favorite functions – EI, frame rate, white balance, and so many more. This level of integration with a camera is unprecedented [...]
List of functions for the GPIO-buttons by Gates