Removable memory devices like USB disks, memory cards and state disks (SSD) as replacement for classical hard drives are very common and their prices are falling. Despite low prices the capacity of such devices is increasing. We have gigabytes of storage in digital cameras, pockets, portable media players and mobile phones. There is one thing that all removable memory media have in common: flash memory. This is a semiconductor non-volatile memory that needs power only during reading and writing. The data written will stay there until the memory chips are not electrically or mechanically damaged. But this applies to the built-in memory chips not to the memory device itself. Any portable device is far more susceptible to damage then other electronics.
The reason lies in the way we use portable devices. We plug them, we save data, then we unplug them, we carry them, then we plug them again, etc. A lot of connections and physical contacts with other electrical devices. Because of this portable memory devices are exposed to static electricity, electrical shocks, high temperature and other conditions. In other words, it is very easy to damage memory card or pen drive. But when a memory device becomes inaccessible it is very likely that the data is still there and can be recovered.
The reason lies in the architecture of removable devices. In general, it is considered of two electronic parts. The first part is the interface electronics (usually a dedicated microcontroller) which takes care for one of the standard interfaces (USB, SATA, Compact Flash, SD, etc.) and connects to the memory. The second part represent memory chips that actually store data. The role of the microcontroller is to receive and buffer data from the external device and to write this data to memory locations of flash chips. For reading the process is reversed. This means that only interface electronics is directly exposed to the external world. And when removable memory device fails it is because a failure in the interface electronics.
To recover the data from removable flash memory cards you need to directly access flash chips. This may look simple but it is not. You need to open the device, remove (unsolder) the chips and read them with special flash memory reader. But you will still not have the original files stored there. This is because you do not know how the data is actually written to the memory. Therefore you need some tool to recover the file system from raw memory data.
Source by I. Funa