-Whether you're looking to sell your iPhone and you accidentally deleted the operating system (I'm looking at you, jail breakers), or whether you want to downgrade from iOS 4, DFU Mode is the place you want to be.
Hi, I'm Seth Rosenblatt for CNET, and today I'll be showing you how to restore an iPhone OS which involves a little jaunt into a Device Firmware Update Mode.
DFU Mode is different from Recovery Mode.
It skips over the current operating system and will allow you to upgrade, downgrade, or just reinstall the OS, and it will wipe any and all data that's on the phone.
It's as close to factory fresh as a used phone can get.
So, before you start mucking about, be sure you've backed up everything.
Start iTunes then connect the phone to your computer.
Do not format the drive if your computer asks you to.
Tap the Sleep/Wake button at the top to turn the screen off.
When you're holding the Home button down, hold the Sleep/Wake button at the same time for exactly 10 seconds, then release only the Sleep/Wake button.
Keep holding the Home button until a message appears on iTunes saying that, "An iPhone in Recovery Mode has been detected." Then you can restore iOS or make whatever other changes you're planning on.
DFU can be tricky to get into.
The easiest way to tell is if your iPhone screen is completely black.
If you see any kind of icon on the screen, it's not in DFU Mode.
Start over and keep at it until you get it.
Also, if you're an OS X 10.6.5 user, there's a known bug that prevents Macs from detecting phones in DFU Mode.
Connecting through a USB hub, finding a Mac on 10.6.4 or earlier, or finding a Windows computer ought to work until the bug's fixed.
So that's how to get your iPhone into DFU Mode.
Remember that precise 10-second count: one Steve Jobs, two Steve Jobs, three Steve Jobs, four Steve Jobs, five Steve Jobs, six Steve Jobs, seven Steve Jobs, eight Steve Jobs, nine Steve Jobs, ten Steve Jobs, release, and hold.