What is dd?
Disk Definition (dd) came from IBM's Job Control Language and became a staple of the low-level UNIX and Linux commands. What dd does is copy bytes from an input source to an output source. But dd can also copy raw data as well, which makes it perfect for copying boot sectors.
The dd command can handle many tasks including:
disk cloning (Note: Target disk must be of equal size or greater than the original disk)
restoring from image file
The dd command is an incredibly powerful tool, so much so it can, if used improperly, do serious damage to data. To that end dd is often jokingly referred to as Disk Destroyer. So, when using dd, you want to use it with caution. In fact, it's always best to practice using dd on non-production machines.