What happens to that information? How can it be destroyed?
In: Technology
A lot of times stuff is still written on your drive after you delete it but it gets marked as available space. So, new things get saved over it and that’s when it’s pretty much gone permanent.
That’s why you have recover deleted file/parts of deleted files using recovery programs
Information can always be destroyed. Imagine you have a line of ten pennies and you flip them all to ‘tails’. The information of their prior state/orientation is gone. That’s basically what computers do when they overwrite/delete data.
Normally, however, when a computer is told to delete something, it doesn’t actually delete it. Rather, it marks it to be written over with the next thing you save.
Imagine you have a lot of bowling pins all down, and you raise some of them forming the pattern of the letter H or the number 5, when seen from above. Next you throw them all down and form another pattern, like the V letter. That’s it.
Instead of bowling pins standing up or downed, you have microscopic magnets biased North Pole or South Pole towards some direction, in the case of hard disks. Or microscopic electrical devices called capacitors that are holding or not an electric charge, in the case of the other type of memories.
The storage is a bit like a checkers game. You have a board with 8×8 square and the game pieces (bits) have one black (1) side and one white (0) so you can flip them,
You store the data by putting them in different patterns. In ASCII code with bits (pieces), you can have the following pattern with a 8 bits per characters
* a 01000001
* b 01000010
* c 01000011
* d 01000100
So you store data be flip bits in the memory to that pattern just like checker pieces. You can delete the data by flipping all to 0.
The difference between a checkerboard and memory the size and you use electrical chare and nog game pieces but the general idea of two possible states in each square is identical.
In practice, especially on hard drives, you do not delete the data but just remove it from the table of contents and it can be overwritten when you store new data in other files. You do the same in a single program but if another program get the same part of memory the operating system change is to only 0
Each physical hard drive has some sort of a table depends on the operation system. This table is located on a permanent address that is given by the operation system. In this table all the files that saved in the hard drive are managed (where each file is located, its size, how many parts this file has, where each part is located…..). So when you delete/make/resize a file the table will be updated accordingly.
And the operation system will know how much space is available and where.
So its not really physically removing the file just removing the “link” to the file.
It depends what kind of memory. I will go over several types:
RAM: RAM memory stores data as electrical charges. These charges need to be “recharged” very frequently (a few dozen times a second). If the electrical supply is interrupted, the charge in the memory will leak out, and the information will be erased. The information can also be erased by purposefully draining the charge out of certain memory locations using an “erase” command.
Hard Drives: Hard drives store data as magnetized particles embedded in a spinning disk. A “read/write” head moves above the disk, and applies a magnetic field that can change the magnetization of the particles. When you erase a file, the write head overwrites the data (pattern of magnetic particles) with other data.
Flash Memory: Many computers have SSDs with flash memory instead of hard drives. Like RAM, SSDs store data in the form of electrical charges. Unlike RAM, these electrical charges don’t drain quickly, so you can leave a flash drive for months or years without power and still have the data. In order to erase data, you send a command to the flash memory to intentionally drain the electricity from the memory locations you want erased.
When you delete a file on your hard drive or SSD, often the file isn’t actually deleted. Your drive keeps an index of all the files on the drive, and where they are stored. When you delete a file, the drive deletes the index entry for that file. The data may still be on the disk, until that area of the drive is over-written with a new file. This is how data recovery programs work, they ignore the file index and hunt for evidence of old files on the disk. You can deliberately delete a file by manually over-writing the region where the file was stored with other data. Drive-wiping programs erase disk by writing random data to the entire drive to make sure all the old data is gone.
It is not (usually) destroyed but the location is freed for reuse.
One might imagine memory as a hotel for numbers. Every room holds one number (always…even if not in use). The operating system or file system keeps track of which rooms are in use and by who (which program or file). Unused rooms are available and are tracked separately. When the memory is allocated, it is removed from the free list and assigned to whoever asked for it. When the memory is freed (or the file deleted), the memory is removed from the allocated list and assigned back to the free list.
Interestingly, “deleting” something only frees up the room. It doesn’t necessarily mean that the value in the memory is lost or even that the person who thinks they have it knows that they don’t. In the movies, this leads to hilarious misadventures and a happy ending. In C this leads to sleepless nights and misery.
If you explicitly want to delete something (which is rare, you only do that if you want to clear passwords or keys), you explicitly store zeros in the space that was storing it.
Otherwise, you have a table that says which memory is being used for what. You just mark the memory as “free”, and at some later point, something that needs memory is going to look for free memory, will allocate the memory (write “using this for x” into the table), then overwrite the data with whatever it wants to store.
It tells the OS to ignore the specific info in that specific place.
You can think of harddrives as shelves. When the computer needs, lets say, that powerpoint presentation you made, it will go to ”shelf #305″ and retrieve it.
When you delete that powerpoint, the operating system tells the harddrive (or rather tells itself) that shelf number 305 on the harddrive doesn’t exist anymore, ignor it, it’s not there.
Information is stored on a computer’s hard drive, as a series of 1s and 0s. When a file is deleted, the actual 1s and 0s are left alone – the computer simply marks that part of the hard drive as unused space. When it needs more space to store a new file, then the old data is replaced with the new.
This is why file recovery programs work – the data isn’t gone, the space where it’s kept is just marked as unused. And also why secure deletion programs exist – if you delete sensitive data normally, it can still be recovered, but secure deletion programs overwrite it to make sure that’s not possible.
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