The Ultimate IOS Guide
This is a Guide from another forum that was copied here to help people.
What is an actual IOS?
The Nintendo IOS officially stands for (I)nput (O)utput (S)ystem. However, for the purpose of this guide we are going to pretend that it stands for (I)ndividual (O)perating (S)ystem. This is because each IOS is basically an O/S. Many people believe that the Wii contains only one bootable O/S, just like your average computer. The reason for this common misconception is that people are often told to think of each IOS as a driver. Whilst it's true that some IOS's do add new features and support for perhipals and devices, they cannot really be thought of as drivers. This is because each IOS is booted separately from one another so they're in fact all completely independent systems. Your Wii CANNOT boot two IOS's simultaneously! They CAN of course call and invoke each other, but NO IOS is reliant upon the existence of another. It's therefore fair to say that the Wii contains multiple O/S (each with its own unique set of drivers).
The only time your Wii does not boot into a standard IOS is when it's in GameCube mode. Instead it boots into MIOS which is a special IOS for running GameCube games. There is only one MIOS and it's rarely updated by Nintendo, as the GameCube is now obviously nothing more than a legacy system. Unlike the Wii of course, which does not even have its own specific IOS.
What are IOS numbers?
The IOS number is best thought of as a chair! Seriously!! Think of your Wii as a table that is surrounded by chairs. Each chair has a number and each IOS sits in its own dedicated seat. IOS60 which is required by System Menu 4.0 would obviously sit in chair 60. If you are on System Menu 4.0 then this IOS will stand up as soon as you start your Wii. The second you login to the Wii Shop IOS60 will sit back down and IOS61 will stand up instead, as this is required by Wii Shop 4.0. However, don't get ahead of yourself just yet and think that IOS60 "is" the System Menu or IOS61 "is" the Wii Shop as this is simply NOT true! They are merely an O/S that is used by the System Menu or Wii Shop and they're both quite capable of booting games too. Each Wii game (including WiiWare/VC games) are coded with the number of the desired IOS best suited to that game. This is why some games contain updates of an existing IOS or a new one entirely. Animal Crossing for example contained and boots from IOS38. This is because IOS38 adds support for the Wii Speak device. Even though games can easily be patched to boot from an alternative IOS (and work fine), an IOS might be optimised (or even required) to run a specific game or device.
Is an IOS region specific?
The number of an IOS is not generally region specific, it's the version of an IOS that differs. I say generally because the Korean Wii currently has its own IOS numbers for some features, such as the System Menu. This may change in the future! Not all IOS's have versions for every region so some can be considered as generic. It's a VERY BAD IDEA to install a version of an IOS that is not meant for the region of your Wii. This can easily be done if you run an update from a disc for an out of region game. You should therefore NEVER update your Wii from an out of region game, as you could easily end up with a BRICK that you may not be able to recover from (especially when 4.0 updates start being released with games).
What is a cIOS?
A cIOS is an official IOS that has been unofficially modified. You might even make the assumption that the "c" stands for custom? Well did you? Give yourself a pat on the back if you did, because you were absolutely right! Well done!! A custom IOS is an IOS that has been modified to do much more or much less than it was originally intended to do. Common modifications include giving you the ability to have Region Free Channels, Skip Disc Updates, Fake Trucha Signing and a Dip Module which allows the IOS to read backups. Some applications such as preloader even allow you to perform your very own low-level patches! Remember that MIOS for the GameCube that we were talking about earlier? A modified MIOS would be known as a cMIOS.
A cIOS that has been modified to work with a particular application such as a Backup Launcher or USB Loader is usually installed to an unoffical slot on the Wii's NAND (internal flash storage on your Wii). Remember the chairs? The slot is the chair! A good example of this is cIOS36. This is the most common cIOS as it's the one used by popular Backup Launchers and Waninkoko's USB Loader. This is installed to IOS249. A backup copy is sometimes installed to IOS250. Therefore cIOS36 is a modified version of IOS36, but sits in chair 249 and NOT chair 36. Why? It sits in chair 249 because it's not meant to interfere with any of the Wii's official IOS's or get in the way of the normal operation of your Wii. The reason it's not called cIOS249 because that would mean that it's a modified IOS249 and there is simply NO official IOS249 to modify.
The first Backup Launchers booted games through IOS249 could not force the disc to use a specific IOS. You probably remember me saying earlier that different games require a different IOS? We used to have to patch the ISO image of the game to use IOS249. This is no longer required as transparent patching through the launchers are now possible, regardless of the IOS required by the disc. Transparent patching of 001 and 002 (unauthorised device) errors have also been added to IOS249 as this was implemented in cIOS36, revision 8. Even though the following fact is not completely relevant; the base for IOS249 was originally IOS37. The base was changed to IOS36 in revision 4 for better compatibility. Another fact that you might be interested in, which is slightly more relevant this time, is that the speed in which backups are read are only 3x speed. The reason for this is because the launcher makes use of a special DVD mode that was written by Nintendo for hypothetical DVD-Video compatibility. This mode only reads at 3x speed and can also only read DVD-R and NOT a DVD+R disc. This does not apply if you're loading backup discs with a mod chip or loading a WBFS images through USB.
What is cIOSCORP?
The best way to describe cIOSCORP is that it's a full set of offical IOS's that have been modified. These modifications include the ability to run backups, transparently patch 001 and 002 (unauthorised device) errors and enable the Trucha Signing Bug. Unlike other cIOS's these ones install back to the original slots (chairs) in the Wii's NAND and REPLACE the official Nintendo ones. This allows backup discs to run on ANY IOS so backups do not have to be loaded through a Backup Launcher or transparently patched to use a specific IOS. Using cIOSCORP is considered much more DANGEROUS than using a launcher because it means that you have to overwite EVERY official IOS. It does however have its advantages and with a patched System Menu it's possible to see all your disc backups in the Disc Channel and load them just like an orginal.
How do I install an IOS?
Official Nintendo IOS's are installed by updating your Wii over the internet or by running the update partitian on a game that contains a Nintendo Update. You can also install them unofficially by downloading a packed "wad" file and installing it manually, by using a homebrew application such as Wad Manager. Other homebrew applications exist that download official IOS files from the Nintendo Update Server (NUS) and install (sometimes patch) them for you. If you are interested in downloading and creating your own "wad" files of an IOS then there is a PC Tool you can use called NUS Downloader.
How do I remove an IOS?
I STRONGLY advise that you NEVER remove an IOS once you have it installed! You DO NOT need to remove an IOS to install an updated or patched version of an IOS. If for example you install a patched version of IOS53 (cIOS53) then it WILL REPLACE the EXISTING one (providing you already had it installed) or it will install to the empty slot (chair). If you must delete an IOS then make sure it's situated in an unofficial slot (chair) and it is not being used by your Sytem Menu. There is a modified System Menu known as a "cSM" or custom System Menu that uses IOS251. If you are using this and you delete IOS251 then you will be left with nothing more than an expensive paper weight (BRICK). At the time of writing the highest official IOS was IOS61. Nintendo did at one point use IOS254, but this was just a copy of IOS9 and was a cheap fix to eradicate the Patchmii Core that was using the same slot (chair). If you cannot anticipate the consequences of removing an IOS then PLEASE DO NOT REMOVE IT - FULL STOP!!
Yes, but I have preloader! BIG DEAL!! Preloader boots BEFORE the System Menu but is RELIANT on the SAME IOS. If you corrupt the IOS used by your System Menu then preloader will usually still function and allow you to fix the problem. However, if you remove the IOS used by your System Menu then you are also in affect removing the preloader! Please bear that in mind if you are the inquisitive type. Unless you have the tools, keys and technical know how to physically flash your NAND, then the only way to recover from a BRICK (which involved the removal of an IOS used by your System Menu) is to pull down your pants, open your wallet and send your Wii to Nintendo.
Official / Unofficial IOS List
The list below represents "my list" of known IOS's. You will NOT have all of them installed (you don't need all of them). Depending on what System Menu you are on the IOS's that appear in RED will result in an UNRECOVERABLE BRICK should you decide to remove them. Any IOS that appears in BLUE are known to be used by many games. Removing these will obviously result in these games not functioning (unless patched to a different IOS). My definition of "game" also means both WiiWare and Virtual Console Titles, aswell as Wii Games.
Official IOS Slots:
IOS3 (Unused Stub)
IOS4 (Nintendo Update)
IOS9 (System Menu 1.0)
IOS11 (System Menu 2.0/2.1)
IOS15 (Nand Loader)
IOS16 (Original Fake Signing Bug - Pinkfish Disc)
IOS20 (System Menu 2.2)
IOS21 (Nand Loader)
IOS30 (System Menu 3.0/3.1/3.2/3.3 + USB Keyboard Support)
IOS31 (Wii Shop Channel 3.0/3.1/3.2/3.3)
IOS36 (Also used by The Hombrew Channel)
IOS38 (Wii Speak Device)
IOS40 (System Menu 3.3 - Korea Only)
IOS41 (Wii Shop 3.3 - Korea Only)
IOS43 (Korea Only)
IOS45 (Korea Only)
IOS46 (Korea Only)
IOS50 (System Menu 3.4)
IOS51 (Wii Shop 3.4)
IOS52 (System Menu 3.4 - Korea Only)
IOS53 (May cause 002 unauthorised device error if left unpatched)
IOS55 (USB Driving Wheel / May cause 002 unauthorised device error if left unpatched)
IOS56 (Wii Speak Channel 2.0)
IOS60 (System Menu 4.0/4.1)
IOS61 (Wii Shop 4.0/4.1/4.2)
IOS70 (System Menu 4.2)
IOS254 (Copy of IOS9)
Unofficial IOS Slots:
IOS202 (USB 2.0 General Homebrew Support)
IOS222 (USB 2.0 Backup Loader Support)
IOS232 (Softchip Rock Band Instrument Support)
IOS248 (Softchip Rock Band Instrument Support)
IOS249 (Backup Loader, USB / SD Loader, USB 2.0 / SDHC Support)
IOS250 (Backup of IOS249)
IOS251 (Custom System Menu)
IOS254 (Patchmii Core)
IOS255 (Patched copy of IOS11 - Remenant from using Xyzzy)
As of firmware 4.2 Nintendo will now install a "stub" IOS in popular unofficial slots and in official slots that are no longer in use by the current firmware. This measure is to block homebrew and prevent piracy. To avoid this you should update your wii using unofficial methods.
FINAL WARNING: REMOVING AN IOS COULD PROVE FATAL FOR YOUR WII IF YOU DO NOT KNOW WHAT YOU ARE DOING!!!