What is the difference between Restore and recovery Mode?
Recovery Mode : Recovery Mode is a state of iBoot that is used during standard upgrades and restores. As iBoot is active, it does not allow you to downgrade your device’s software. Also, unless it is ‘pwned,’ it will not allow custom firmware to be flashed.
DFU Mode : DFU Mode is a special mode where the device can still interface with iTunes, yet it does not load the iBoot. The screen will appear totally black in DFU mode, so you can’t guess whether the device is in DFU or powered down from simply looking at the screen. Because iBoot and the OS are not loaded this exploit makes us able to downgrade your iPhone firmware or upgrade with a custom firmware created by Pwnage tool.
How to put your iPhone in recovery mode :
- Turn the device completely off and disconnect it from cable/dock.
- Hold down the home button.
- While holding down the HOME button connect to a computer with a cable (easiest) or dock.
- Keep holding down the home button until you see a connect-to-itunes screen You are now in recovery mode.
To escape Recovery Mode and power the phone off simply hold down power and home buttons for ten seconds.
How to put your iPhone in DFU mode :
- Connect your iPhone to your computer.
- Turn iPhone off.
- Hold power and home together for 10 seconds (exactly).
- Release power but keep holding home until the computers beeps (observed on a PC) as a USB device is recognized.
- A few seconds later iTunes should detect your iPhone.
- If the Restore Logo is present on the screen, you are in Recovery Mode, not DFU.
Another step-by-step Source taken from iClarified, click --> HERE
DFU means Device Firmware Update. If a restore using Recovery Mode doesn't work you will want to use DFU Mode as a last resort. When placing your iPhone into DFU Mode it does not load the OS before attempting the restore
To put the iPhone into DFU mode so you can do an iTunes firmware restore follow these steps: Step One
Open iTunes and connect the iPhone to your Mac.
Press and hold the Home button and the Sleep/Wake button at the same time.
After exactly 10 seconds release the Sleep/Wake button. Continue holding the home button until you iTunes pops up a message telling you that it has detected an iPhone in recovery mode.
The iPhone screen will remain black like this:
NOTE***: It may take a few attempts to get your iPhone into DFU mode. Generally, I hold down both buttons then release the Home button just before I think the Apple logo would appear. If you are still holding both buttons down and you see the Apple logo you are holding them down for too long!