what is mean by cloning??
Cloning is the act of duplicating the contents of a hard drive from one physical drive to another. There are two types of cloning. One is a smart clone that clones at the file level and doesn't copy unnecessary files or blank sections of the drive; it can also grow or shrink partitions to fit the new drive. The other type of clone is a sector or forensics clone. It copies everything from the source drive sector by sector, unaware of the contents of the drive and even copies empty areas of the drive. This makes the sector clone very slow and inflexible because it copies the whole drive (not selected bits of it), and won't resize any partitions, thus making cloning to a smaller target drive impossible. But with a sector clone you can clone just about any drive regardless of the file system or OS on it.
So a common use of a clone is moving to a bigger hard drive without reinstalling Windows, reinstalling all your applications and moving over your data. You can clone your original hard drive to a new drive, swap the old drive out for the new one and boot the computer to an exact duplicate or "clone" of the prior system. Everything will work exactly as before and all your data will still be in the same place.