Modes

At any given time an iPod can be in one of several modes, some of which can be activated by holding down certain buttons while the iPod is booting.

Normal mode

"Normal mode" is when the iPod is booted into retailOS normally. In this mode the iPod presents as a mass storage device to a computer, allowing files to be transferred. Receiving device information from the iPod, as well as updating the iPod's Firmware, can be done from normal mode through the use of proprietary SCSI commands.

Disk mode

In disk mode, like normal mode, the iPod presents as a mass storage device to a computer and can have its information read and firmware updated. When in disk mode, the iPod screen will display, with a black foreground and white background, either a no symbol with the text "Do not disconnect." or a checkmark symbol with the text "OK to disconnect." depending on whether the iPod is connected and if it has been ejected.

Disk mode exists on all iPod models. For more information on how to enter disk mode, refer to this Apple support document

Disk mode is also referred to as "forced disk mode" in device information received from the iPod.

The place where disk mode is stored on the device differs depending on the iPod model. On the iPod nano (4th generation) and newer, disk mode is stored in the "disk" partition of the Firmware.

DFU mode

Device Firmware Upgrade, or DFU, is a standard for upgrading firmware over USB that is used by many devices, including iOS devices and newer iPods. DFU mode exists on the iPod nano (3rd generation) and newer and the iPod classic (6th generation) and newer, coinciding with Apple's switch from PortalPlayer to Samsung processors. DFU mode is contained in the on-processor BootROM. Instructions on entering DFU mode can be found here.

When in DFU mode, the iPod can be sent a special WTF IMG1 firmware image to enter WTF mode. Other IMG1 images cannot be sent in this mode.

The iPod nano (2nd generation) also has a DFU mode, but it can only be entered by shorting testpoints on the iPod's circuit board or flashing the NOR with an image with an invalid signature or hash. It does, however, support a NOR DFU mode that can be entered by holding down Back+Play right after rebooting the device.

WTF mode

In WTF mode (possibly 'Where's The Firmware?'), the iPod will accept any IMG1 image it is sent over DFU and, if signature and decryption checks pass, will attempt to boot to it. It is entered from DFU mode when a specific WTF IMG1 firmware image is sent. While in WTF mode the iPod still uses the standard DFU protocol.

The iTunes behavior upon seeing an iPod in WTF mode is to send it a "recovery" firmware image, which places the iPod in disk mode. However, any firmware image can be sent to it, including, for example, the "osos" partition from production iPod firmware, which enables tethered booting an iPod into retailOS.

Diagnostic mode

This mode will give quite a lot of info about your iPod. Except for the very first iPods, it can be accessed by holding center and rewind when the apple logo appears during reboot.^{(clarification needed)}

USB IDs

When connected to a computer, the iPod presents a vendor ID of 05ac (Apple Inc.) and a product ID that depends on its model and which mode it is in:

Model		Normal/disk mode	DFU mode	WTF mode
iPod nano (2nd generation)		1260	1220	1240
iPod nano (3rd generation)		1262	1223/1224	1242
iPod nano (4th generation)		1263	1225	1243
iPod nano (5th generation)		1265	1231	1246
iPod nano (6th generation)		1266	1232	1248
iPod nano (7th generation)	2012	1267	1234	1249
	2015			124a
iPod classic (6th generation)	Initial	1261	1223	1241
	Rev A			1245
	Rev B			1247
	Rev C			1250