A system update is a collection of updated titles installed via the “Wii System Update” feature, either from a disc or over the network. The System Menu is typically updated, along with certain IOSes, and sometimes some channels.
While system updates are generally referred to by version, the Wii does not store a firmware version anywhere, besides the System Menu version, although not all system updates come with a System Menu (for example, the Oct. 23 Update).
The first title to be updated in each update is boot2, whose contents are instead passed to ES_ImportBoot, in an attempt to safely update both copies of boot2. After this, the System Menu IOS is installed, followed by the System Menu itself. The rest of the updated titles are simply updated in the order they are found.
The most common method of installing an update is by pressing the update button in the settings. When doing this, the System Menu takes the version number of boot2, the System Menu, and a single IOS, and uploads them to NUS. NUS then returns the latest version of al title.
From here, the System Menu downloads each ticket and TMD from NUS that has a later version than the version installed, or is not installed, as well as the contents listed in the TMD. These are fed to ES and installed.
When a disc is inserted, one thing the System Menu checks is whether any titles in the update partition have a version higher than the one on the NAND; if so, the "Wii System Update" banner is displayed on the Disc Channel instead of the normal banner (only on 3.2 and higher).
When the Disc Channel is clicked, a prompt to update appears. For each title with a version number higher than that on the NAND, and each title that does not already exist on the NAND, the title contents are fed to ES's title installation ioctls.
On the vWii, updates are done together with Wii U updates. The upper bits of the title IDs are modified to distinguish from Wii titles, which prevents things like the NANDLoader from appearing on the normal Wii. This mapping is only done on NUS; the actual titles are still installed into the normal locations in the vWii.
|NUS ID||vWii ID|