The NOOK Tablet (whose older cousin is the NOOKcolor eReader, and whose closest competitor is the Amazon Kindle Fire) and dozens of other tablets all share one important element in common: They use the Android operating system. Android was developed by the globe-gobbling guys and gals of Google.

Apple keeps the iPad’s iOS operating system locked under glass (and RIM does pretty much the same with the BBX or BlackBerry 10 code for the PlayBook), but Google has been very open with its product, which is generally a good thing.

However, every developer of hardware that uses Android is free to make modifications or add a restrictive outer shell on top of the operating system. That’s the situation with Barnes & Noble, which keeps a tight grip on the system within its NOOK Tablet and the NOOKcolor.

If you follow all of their rules, you can only install apps that are approved by — and sold by — B&N. And you are also unable to modify the operating system or replace it with another.

That said, technology is a continual game of cat-and-mouse. For whatever reason, dozens (if not thousands) of people dedicate uncounted hours to finding chinks in the armor so they can have their way with the NOOK Tablet.

The holy grail is the ability to root the system. This means finding a way to get at the deepest (or lowest) level of the operating system and make changes. Or the rooters may want to substitute a different version of Android with added features and no restriction on apps.

That’s the place B&N would rather you not go, of course, because tinkering with their operating system may cause the device to become unsupportable. It may also cause your device to become more vulnerable to hacking attempts. Rooting around with the NOOK Tablet will void your warranty with B&N.

If you really want or need a tablet with features beyond the fairly complete set offered by Barnes & Noble, you can always buy a different device. Besides, B&N can — and has — made a number of updates that have closed loopholes that hackers try to exploit.