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IOS is the operating system that runs on the Starlet coprocessor inside the Hollywood package. It provides the services that are used by Wii code to access most of the system devices.

See also: IOS/QA


Communication with IOS from PPC code is done using an IPC mechanism. There are 7 calls that can be made using this system:

  1. open
  2. close
  3. read
  4. write
  5. seek
  6. ioctl
  7. ioctlv
ipc struct size = 0x40, aligned to 0x20

00:     cmd     // 1=open 2=close 3=read 4=write 5=seek 6=ioctl 7=ioctlv
04:     ret
08:     fd
0c:     arg[5]
20:     async1
24:     async2
28:     0
3F:     relaunch, used for ioctlvreboot

open:   fd = 0
        arg0, arg1: name, mode (1=read 2=write)

close:  fd

read:   fd
        arg0, arg1: addr, len

write:  fd
        arg0, arg1: addr, len

seek:   fd
        arg0, arg1: where, whence

ioctl:  fd
        arg0: ioctl #
        arg1, arg2: addr, len
        arg3, arg4: addr, len

ioctlv: fd
        arg0: ioctl #
        arg1: # in
        arg2: # out (or in-out)
        arg3: pointer to # in plus # out pairs of (addr, len)

fd is a handle you get back from ios on "open", and that you should pass back to all other calls --segher

Most non-trivial operations are performed by opening one of the below resources, then calling ioctl or ioctlv on it.

The Starlet kernel hands these calls over to the individual drivers / processes within the Starlet. The processes register themselves to handle requests by creating one or more queues and assigning them to handle requests from a particular /dev device.

IOS Modules

IOS is a Nintendo-proprietary, embedded operating system. It uses a microkernel architecture, with several independent modules that talk to each other via "resources", which are organized as entries in the /dev tree.


The Kernel is the piece of code that is actually booted; it contains a small ELF-loader header at the beginning, and then is an ELF file. In addition to the core microkernel stuff, it contains the bare minimum drivers necessary to read the rest of the drivers from the NAND filesystem -- specifically, FFS (Flash Filesystem), ES (E-Ticket Services), and IOSP (Responsible for booting and managing Broadway?).







  • /dev/net/kd/request
  • /dev/net/kd/time


  • /dev/net/ncd/manage
  • /dev/net/wd/top (Yes, this is actually created by NCD, not WD)