However, as known to all, there is a risk of data loss during i OS device firmware update.

Therefore we would like to highly recommend you back up i OS device (i Phone, i Pad and i Pod) before you install IPSW file with or without i Tunes.

For Mac users, launch i Tunes, select your phone on the left sidebar hold down the Alt/Option key and click on restore so as to browse downloaded IPSW file for restoring.

For Windows users, after connecting your i OS device to i Tunes and launching i Tunes, hold down the Shift key and click “Restore” to force i Tunes to restore custom IPSW file.

DFU or Device Firmware Upgrade mode allows all devices to be restored from any state.

It is essentially a mode where the Boot ROM can accept i BSS.

DFU is part of the Secure ROM which is burned into the hardware, so it cannot be removed.

On A7 devices, it generates an Ap Nonce and recognizes APTickets as well, so even in DFU, it can accept an APTicket.

For more information on the protocol, see DFU 0x1227.

Please explain this for me.” For those people who have restored their i Phone, i Pad or i Pod quite often, IPSW is no stranger.

As mentioned above, when you connect an i OS device (i Phone, i Pad or i Pod) to i Tunes and choose to update your i OS device firmware, i Tunes would automatically download IPSW file for your device connected.