Hmmm. . . . that's a good question. . . . .early models were, I believe, based somehow on linux. But I might be wrong about that -- it's not something I ever paid close attention to. As long as it works, I'm happy.
There's another forum, mobileread.com, where a lot more techie types hang out. We're the BEST, site, of course. but the folks there are very helpful with theses sorts of questions.
What exactly is the reason for your question? Are you looking to write apps for Kindles? The Kindle Fires use a forked version of Android, so Android apps (which are written with a particular Java API) should work on them with little to no modification. E-ink Kindles run a custom OS based on a Linux kernel. To write apps for them, you will need to apply to be a developer at http://kdk.amazon.com/, which is apparently still in beta after several years.
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