What it comes down to, however, are three main options. All of them take advantage of the configuration that makes the NC so flexible in the first place; unlike most Android devices, the NC boots first from the ɥSD slot, in the same way a PC looks first for a bootable disk before loading the OS on the primary hard drive. As with a PC, this configuration makes it very easy to run a utility, install an OS, or even run an OS completely from bootable* ɥSD.
When used as a verb, rooting means altering your current stock firmware to enable root, or superuser, access. Like having the Administrator account on a Windows PC, root allows you to change high-level settings such as those preventing you from installing unapproved apps, and accessing unapproved app markets. Rooting the NC maintains the stock interface, the stock reading app, and device-specific perks like in-store reading, but lets you install the Google and/or Amazon app markets, which have many more apps than the B&N market, often at lower prices. Apps purchased on those markets can also be installed on other Android devices.
If you basically like the NC's interface but would like a couple more apps, rooting may be your best option. The most common way to root the NC is ManualNooter. If rooting stock firmware 1.4.x, follow the linked instructions but use ManualNooter 5.12.20.
Custom ROMs (OS replacement)
Custom ROMs are volunteer-built operating systems that completely replace stock firmware when installed on a device. Virtually all custom ROMs have root access by default, and do not need to be rooted. Because we can boot from ɥSD, it's also not necessary for us to root before installing a custom ROM, as is necessary on many other Android devices. For the NC, there are three ROMs worth considering, and one to rule out.
- CyanogenMod7: The CyanogenMod project is a robust team of developers releasing nightly improvement of their ROMs for a variety of Android devices. CM7, a version of Android 2.3 Gingerbread, is by far the the most feature-rich and flexible ROM for the NC, with the most community support. CM developers have added features like bluetooth, Tablet Tweaks, audio improvements, USB host, and more to the NC. Replacing B&N stock with CM7.
- MiRaGe CM7.2 KANGs: With the CM7 team no longer providing quasi-nightly test builds, this ROM is the simplest way to keep up on the latest changes until there's a new stable CM7 build.
- MIUI: a popular makeover of Gingerbread's UI, brought to the NC using CM7 codebase.
- Honeycomb: the only versions of Honeycomb available for the NC are basically demos and are not being updated. Honeycomb is the only Android version for which Google has not released source code, so there is very little for devs to work with.
Custom ROMs (ɥSD install)
The NC's fairly unique configuration opens up a third option that leaves the stock firmware untouched and arguably preserves your warranty (though I still wouldn't mention it to customer service). Because it boots first from a ɥSD card, and that card is virtually identical to the internal flash storage (eMMC), it's possible to run a custom ROM entirely from ɥSD. This option is probably the best place for most people to start, even if you think you'll eventually be replacing the stock firmware. It's a fairly simple procedure that leaves you in a good position to make future changes if you decide they're necessary. With the right card (see instructions), many people find ɥSD installs to perform just as well as an OS housed on eMMC.
For the more adventurous or more particular, you'll find a variety of projects on the xda-developers NC forums, such as moving your stock firmware to ɥSD. I've also assembled a guide for dual booting two OSes from eMMC.
*Perhaps the least familiar aspect of all these methods, where a lot of people run into trouble, is writing a bootable image to ɥSD. A couple of things to keep in mind:
- Your laptop's all-in-one cardhole probably won't work. Even a regular-size SD slot and an adapter may not work. Some people (including me, making my first card) have success using the NC, a phone, or a camera as their reader via USB, but if the connection is interrupted, the card may be rendered unreadable. Your best bet is a USB ɥSDHC reader, which are quite inexpensive.
- Downloads get corrupted. Check the md5 sum of your image files if available, or if an image doesn't write successfully, delete and re-download.