where is all deleted data will go from a memory system ? if it is not deleting actually where it storing ? i am always wonder about this when we are sending something to a memory system it takes long time (depends up on usb port) and when we are deleting it not taking more than a bling of eyes and disappears actually where it goes ? ** deletion process is happening on both memory device and internet is same or different ** ? can we recover data from internet ?
closed as off-topic by David Richerby, Luke Mathieson, Raphael♦ May 20 '15 at 7:40
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "This question does not appear to be about computer science, within the scope defined in the help center." – Raphael
Deleting is not necessarily destroying data. It can be done (much faster, indeed) by making it inaccessible. You can do it by erasing critical information from the data structures that are used to index the data you want to delete. How exactly this is done depends on how the storage device is organized (formatted).
First there is the answer already given by André Souza Lemos. The data need not be destroyed. It is usually sufficient to mark the corresponding space as unused in some table, so that the system will no longer try to read it: it considers that there is nothing stored there. But the data is often still there, often fairly easy to find, even when some key organization information has been destroyed. That is why deleting data is fast: it is not done, unless actually replaced by some other data in the same memory chunk (and even then ...), and that would take time as you expect.
Actually, back in history, the way MS office used to save documents on disk was such that it copied on disk large chunks of main memory of which it had used only some part. So the file thus created did contain whatever data was lying in that unused part of the chunk of memory when it was attributed to MS Office as work space.
So you saved an edited document on disk thus creating a file, and part of that file contained whatever junk was lying in the main memory of the computer in some subpart of what was attributed to Office. Then you send your innocuous document around, for example to invite friend to your daughter's birthday, and you find out much later that it contained also your credit card number, or a love letter to someone not your spouse, that you thought erased from your computer.
You cannot really rely much on your computer for destroying data it is not supposed to keep.
Now, for data in volatile memory, it is usually enough to turn off the computer. That is the case usually for the registers and main memory, but not for the disk.
So for data stored on disk, if you wand to destroy the information stored in a file, you have to identify the location of that file and store something different in the same location. This is not necessarily easy for the average person. Another possibility is to completely overwrite the disk, to make sure you do not miss any location. This make take some time when you have 5 TB, but there are applications to do it.
With that you are pretty safe from most eavesdropping. But not completely: I once read that disk are not precise enough to always write exactly on the same spot for a given address, so that, with very advanced tools, forensic investigators can read the former content of a disk that has been overwritten several times. I do not know how much is true.
There is probably a lot more to be said, and more precisely. But the conclusion is: if you want to keep your secrets safe: don't tell your computer. It tends to remember too much and occasionally to repeat what it knows.