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'''IOS''' (speculated to be short for "Independent Operating System", "Input/Output System", or "IOP Operating System") is the operating system that runs on the [[Hardware/Starlet|Starlet]] (IOP) coprocessor ([https://wiiubrew.org/wiki/Hardware/Starbuck Starbuck] on the [[vWii]]) inside the [[Hollywood]] package. It provides services that are used by Wii code to access many system devices: USB, networking, security, app management, NAND flash storage, SD card, optical disc, and also WiiConnect24 features.
'''IOS''' (speculated to be short for "Independent Operating System", "Input/Output System", or "IOP Operating System") is the operating system that runs on the [[Hardware/Starlet|Starlet]] (IOP) coprocessor ([https://wiiubrew.org/wiki/Hardware/Starbuck Starbuck] on the [[vWii]]) inside the [[Hollywood]] package. It provides services that are used by Wii code to access many system devices: USB, networking, security, app management, NAND flash storage, SD card, optical disc, and also WiiConnect24 features.
−All software using the Wii SDK or [[libogc]] relies on a running IOS on the Starlet (with a few exceptions in the latter case - it is possible to shut down IOS services from libogc and work without it). Typically, the only times IOS is not in use is when running GameCube software (which uses [[MIOS]] instead - effectively a dummy IOS), or when [[BootMii]] and related software is in use (which uses [[mini]] instead).
+All software using the Wii [[SDK]] or [[libogc]] relies on a running IOS on the Starlet (with a few exceptions in the latter case - it is possible to shut down IOS services from libogc and work without it). Typically, the only times IOS is not in use is when running GameCube software (which uses [[MIOS]] instead - effectively a dummy IOS), or when [[BootMii]] and related software is in use (which uses [[mini]] instead).
IOS is versioned in a somewhat unique way. Instead of there being a single canonical version of IOS, there are multiple branches, each typically corresponding to one or more versions of the Wii SDK. Each branch is apparently specified to have a completely frozen API, and old versions are only updated to patch bugs (often security bugs) - Nintendo at one point created an entirely new IOS branch that differed only in the default value for the TCP buffer size. A fully updated Wii contains one copy of the latest version of each branch of IOS. On a Wii, these are installed as separate titles, often called "IOS slots". Due to this design, it is generally considered safe to uninstall, reinstall, or patch an IOS or IOS module, as long as it is not the slot used by the System Menu - if anything goes wrong, the broken version can be safely uninstalled and a vanilla copy reinstalled. IOS slots have title IDs 1-3 through 1-255. Unused (high) IOS slots are often used to install patched versions of IOS or alternative Starlet software (e.g. [[BootMii]] as IOS is installed as IOS254, which when invoked will subsequently load armboot.bin from the SD card, typically [[mini]]). See [[IOS History]] for a comprehensive list of IOS slots and versions.
IOS is versioned in a somewhat unique way. Instead of there being a single canonical version of IOS, there are multiple branches, each typically corresponding to one or more versions of the Wii SDK. Each branch is apparently specified to have a completely frozen API, and old versions are only updated to patch bugs (often security bugs) - Nintendo at one point created an entirely new IOS branch that differed only in the default value for the TCP buffer size. A fully updated Wii contains one copy of the latest version of each branch of IOS. On a Wii, these are installed as separate titles, often called "IOS slots". Due to this design, it is generally considered safe to uninstall, reinstall, or patch an IOS or IOS module, as long as it is not the slot used by the System Menu - if anything goes wrong, the broken version can be safely uninstalled and a vanilla copy reinstalled. IOS slots have title IDs 1-3 through 1-255. Unused (high) IOS slots are often used to install patched versions of IOS or alternative Starlet software (e.g. [[BootMii]] as IOS is installed as IOS254, which when invoked will subsequently load armboot.bin from the SD card, typically [[mini]]). See [[IOS History]] for a comprehensive list of IOS slots and versions.
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When the Wii is in WiiConnect24 standby mode (yellow LED), the main PowerPC CPU is off, but IOS is still running.
When the Wii is in WiiConnect24 standby mode (yellow LED), the main PowerPC CPU is off, but IOS is still running.
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+The [[IPC (SDK)|IPC]] SDK library seems to have copies of some IOS syscalls such as IOS_AllocAligned; this may mean IOS was originally planned to be part of the SDK, but that was scrapped when there was no way to keep that secure.
== See Also ==
== See Also ==