This would suggest a hardware interface to something external that has memory capabilities?

How does this work in the Editor, and what would be the Hardware Interface to accomplish it? 
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External variables are not external to the hardware, but external to the context of the program or function that you're writing. They're like global variables. So, if you're writing a function to add two numbers, if one of these numbers is declared as External, it can be accessed by other functions or by your main program.
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