Some comments and questions

[gorosito]

Hi, finally I could erase the unused space in my HDD. I used PCI File Recovery to see how well Earser did it. The results show a lot of deleted files without names and 0 size, i.e. I think it is impossible to recover them. At this point it seems Eraser works Ok. But I am wondering if there's a possibility those files can be recovered. I don't know if starting with a basic recognition of the possible existence of some files (even not knowing the name and size) a more powerful app than PCI File Recovery can do the job of getting the whole data.
Could the existence of those traces of files lead to find the complete structure and content of the deleted files?

 

[Gralfus]

The short answer is "no". Eraser overwrites the locations where the file data was located. By analogy, if you had a sheet of paper with a normal English paragraph on it, if you replace each existing letter with a random new letter, that is what Eraser does. I've done repeated tests with a variety of files and examining the results in a hex editor before and after Eraser. Eraser does what it claims to do.

 

[JRd1st]

Overwriting once or twice can be counterbalanced with the use of an error filter, and old data can thereby be brought to the surface. This is thanks to the physical effects which result from the analog signals of 0 and 1. These never really represent 0 or 1, but are distorted to 0.05 or 1.05. The hard ware counterbalances this defect with tolerance levels meaning that 1 can be saved as 0.95 or 1.05. By using these variations, a microanalysis of the relevant data signal can provide information about previous data values. If a 0 is replaces another 0, this gives a different signal strength than if a 0 replaces a 1. This process is not exactly easy or cheap, but it shows that simply overwriting the data does not delete them. For this reason, the most common erasure methods are always overwritten with a data value and its complement in order to make this “difference method” impossible.

Source:
http://www.oo-software.com/en/docs/usersguide/oosev3.pdf