How does does data recovery on flash memory work?

I understand generally the technology involved in data recovery on magnetic media, but would like to know how data recovery is possible on flash memory? How is there any trace of deleted data? How does the software do this?How does does data recovery on flash memory work?
There are two forms of data recovery for flash memory, one in response to physical hardware failure, in which case it is usually an interface issue, and specialized hardware is required to do this as the interface is physically replaced.





The scenario it appears you are asking about is the second, in which the data has become inaccessible but still resides on the flash memory. This would be due to issues such as a virus infection, failure of interface programming in the USB Flash Device, etc.





In this case, essentially what the software attempts to do is instruct the USB device to pour out a copy of everything it contains so that the software can attempt to make sense of it instead of the USB device translating into an operating system friendly form.