In most partition recovery software, to locate all partitions on a damaged hard drive, you have to scan the entire surface. The process, which is often pretty much useless, may take up to several hours of your precious time, and it may even take days if the hard drive is filled with bad blocks. In the worst case scenario, it can make significant damage to the hard drive, thus making the data recovery process much more complicated and expensive.
While the need of scanning the entire hard drive might look reasonable, in vast majority of cases it is not needed. Furthermore, there’s no need to scan more than 1% of the HDD surface to locate all partitions! This is because of a simple fact that there are not too many places where a partition can start and end.
First of all, Windows Disk Manager (and almost every other partitioning software) creates partitions in 8 MB increments. This means that to locate all Boot Records of all partitions, you need to read one sector, and then jump over 16064 sectors, read one sector and so on. Yes, that is 16065 times less data to read than when you scan the entire drive. Fascinating!
Second, when a partition has been found, it is often easy to find out how big it is (by parsing its Boot Record, if it is looks intact). This information allows you to just jump over that partition and continue looking for other partitions.
Finally, it turns out that in most cases a good partition recovery software needs to read just a few sectors! There are exceptions, of course, but they are rather rare and can be dealt with.
I am not trying to say that partition recovery is a simple process because it is not. My point is: partition recovery software can be much faster, efficient, and user-friendly.