What is an IOS and why should I care?

The Wii runs on an operating system which is broken up into many Internal Operating System (IOS) files. You can learn about the many IOS files on the WiiBrew IOS History page. For example, IOS36, IOS37, and IOS38 are official IOS files which are generally installed by Nintendo onto your Wii system. Only one IOS can run at a time.

Hackers of the Wii will utilize and modify the functionality of the official IOS files to their own end. When they put together their own IOS, it is referred to as a custom Internal Operating System (cIOS). These cIOS files are often built up from official IOS files and then installed as a new file, on your Wii they will always simply be labeled as an IOS.

Waninkoko originally modified IOS36 and installed it as IOS249. Later he modified IOS38 and installed as IOS249 or IOS250. Hermes modified IOS37 and IOS38 and installed as IOS222 or IOS223, allowing for multiple install versions. This way you can install a modified IOS37 as IOS223 and a modified IOS37 merged with IOS38 as IOS222. For the most part, the latter is all you will need. The other cIOS versions and install methods are for trying different methods of modification to allow for different attributes.

At the moment, there is no summary page discussing all the capabilities of all the cIOS options available.

I hope this helps you understand all the babble, but feel free to ask questions if you need further clarification. 

You can also read more detailed information about the IOS and the hardware of the Wii at WiiBrew in the following articles:

IOS - Internal Operating System

Starlet - ARM9 Input/Output bridge for Hollywood, handles I/O and security 

Hollywood - Wii Graphics chip

Broadway - Wii CPU