hi, i would like to know is there any disadvantage formatting hard disk, is it possible that my hard disk may corrupt or damage especially older hard disk, if it is what the safest way to format older hard disk.
The disadvantage is that you will erase all the data on the disk. Other than that (which is pretty significant!) there's no physical harm in formatting a drive, although it won't help if the drive has a mechanical or electronic fault.
You format a drive by going into Windows' "Disk Management" console (Start -> right-click "Computer" -> Manage -> click "Disk Management" in the left pane. Once there, find the drive in the lower portion of the right pane and right-click on it.
If you want to format the Windows drive itself, then you need to boot from the Windows installation disk - during the install procedure you can delete the existing partition(s) from the disk and create new ones - if you do this then they will be formatted as part of the installation.