DataRescue's DD (in short DrDD) - is a graphical disk imager intended for data recovery and backup of partially corrupted storage devices. DrDD creates complete or partial images of disks or memory cards to files on another storage device, allowing multiple data recovery attempts on the raw data, thereby minimizing the risk of damaging the corrupted media further. DrDD is available for Windows PC and Mac OS X machines.
The theory of operation appears like nice.
A typical use example
A 40GB hard drive suffers of physically bad sectors in the system area that cause the drive to lock up when the damaged area is hit by a conventional disk duplication program or a data recovery program. DrDD is first used to attempt an image of the drive. DrDD locks up as well, the error is completely irrecoverable. The system is reset. Through the last log, the problematic area seems to be sector 1.000.000. DrDD is used to first create an image of the hard drive up to sector 999.999. Knowing that hardware errors are often contiguous, a second image is created, backwards, from the end of the drive (for example 40000MBs) back to sector 1.000.001. The backward copy proceeds and finally locks up at sector 1.004.000. If the data hasn't been saved, a new forward copy starting at sector 1.004.001 and going up to the end of the drive is done. The user now has saved most of the raw content of its hard drive and has saved the multiple trial and error read attempts he would have gone through if he had restarted the copy forward at sector 1.000.001 - with most of the data in a safe place, the user is now able to try as many data-recovery utilities as he wishes, for example our own PhotoRescue application.
It can be however be used as a "normal" imaging tool (if source is not defective).
Though biggish (for my "standards") it's a self-contained no-install .exe, about 2.3 Mb in size that can even run from within a .zip.