David W. answered • 10/28/15
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The answer to your question has multiple levels of complexity with different types of storage media, so I will answer it for pen drives, internal memory, disk drives, and CD/DVDs.
(1) Some memory/storage is volatile. That means that the information stored in it is quickly lost when power is no longer supplied. This type of memory is useful for fast, internal memory. Most computers use it for internal memory.
(2) Some memory/storage is "write once." The letter "R" on CD-R and DVD-R indicates that this storage allows a one-time, permanent change. It is cheaper that read-write media and is great for items that won't change -- music, distributed software, etc.
(3) Read/Write, non-volatile memory/storage. This includes the old diskettes, tape storage, that pen drive, CD-RWs, DVD-RWs, etc. It should be noted that "permanent" does not mean "eternal," because these media/storage can be damaged and do lose their ability to retain the magnetic charges or light because they simply get old and wear out.
Now, consider how data is stored in files on memory/storage. There are directories and file names that provide an index to the location of the actual data. Many, many operating systems save time when "deleting" files by simply changing the directory entries so that the data space they point to may be reused. The actual data is not changed and special software (or a person with a program to dump the directory index area) may change the index so that the data space is now allocated to another file (perhaps, even with the original name). These are called "undelete" programs and are widely available. So, when proprietary or classified or personal data is deleted, it is wise to write new information into that data file area in addition to deleting the file name in the index. Often operating systems provide this as an option to the delete operation.
When that pen drive you mentioned stores that other, new 4GB of data, the memory locations are changed to contain the new values. This does mean that the original information is permanently overwritten and lost. That is because a pen drive has individual mini-electronic circuits that store the information. You are correct. However, please remember that the delete operation changed the directories and the re-write operation changed the data area, so portions of the directory may still have useless file names and file information that no longer point to the original data. So, a more thorough "reformat" is required to overwrite them.
Now, other memory/media like tapes, disks, etc. have information that identifies "tracts" and "start/stop" locations of data. The media actually can store continuous data. This means that some of the old data may not be totally destroyed when the new data is written. The old information may or may not be recoverable, very sensitive equipment is required to do this, and very specialized software (which can process lots of partial results) is required. However, it does exist.
Keep thinking and asking these questions. Many people don't know the answers (so their data is vulnerable).
David W.
Sure ... post your comment/question.
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10/28/15
Nandakumar N.
we can share or store our data in internet, how they secure that data and where that data were stored,
All the information on internet are stored in a single place or either in different places?
If it is different place means how they unite that in a single point?
That on line storage also same as pen drive or that also temporary?
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10/29/15
David W.
To answer these questions, it help to know the history of computer processing and computer storage.
The first computers were large, slow, and "stand-alone" (that is, not connected to each other). They each had their own processor, internal memory, and external storage. Media such as tapes and diskettes were used to transfer data from one computer to another. There were also "dumb" (no processor) teletypes and cathode-ray terminals that allowed a person to access the computer using a telephone line (dial-up or direct) connection. It was possible for computers to look like terminals to other computers so that information could be transferred between computers.
After a few years, the speed of phone connections and the wiring used became good enough that direct computer-to-computer connections were pretty fast (by comparison to older methods). "The internet" began as a file transfer capability between computers that were far apart. The software and equipment allowed for just a few hosts because most real processing and storage of information still happened on each computer locally. The transfer of data to another computer was an extra step for processing and storage.
Lots of hardware (equipment) and software improvements happened over a couple decades. Personal computers arrived -- with their own processor, storage -- and with a communications capability. Storage media became cheaper and cheaper with larger and larger capacity. Communications became faster and faster. Software became much more complex. ... The result was that there were local networks with servers that had more storage than workstations. The Internet connected these local networks. (Special note: the Internet is a connection of networks, not a connection of workstations.) Now, it was possible that another computer could run your program, store and process your data (from a disk or tape), print your report, etc. and look as though it was part of the computer workstation on your desk.
To answer your first question, we may now store our data either using our own computer or a server on our local network or a storage provider on the Internet. Many companies sell and provide free storage space on huge collections of inexpensive disks. Most of these are still disk technology, but cost and speed usually determines the specific media used. In each case, making (and testing) backup copies is important, securing access to computers and backup media is important (encrypting data helps to keep data unreadable by someone else), and maintaining the integrity of data (don't let someone send me a virus, change my bank or medical data, or even monitor my keystrokes) is important.
Software developers can no longer simply write programs to solve problems then add a layer of security to the program; they must design programs that check and ensure accuracy and integrity of data, restrict access to data (much like military security levels), and control permission to run the programs. There's much more here. So, every day, there are companies (or government) agencies that have data accessed or modified by unauthorized people (actually, few of these make the news).
Internet sites store data at many, many locations. There may or may not be enough duplicate copies of data to recover from a major disaster (fire, earthquake, etc.). We may or may not be able to specify where our data is stored. This is a very rapidly changing situation called "cloud storage."
The security of "cloud storage" is a big, big problem. Even if data is encrypted, backed up, etc., there have been cases where very private photos of celebrities have been obtained from personal could storage. It might even be someone who works at one of these sites.
Uniting data is a technology problem. Even though it sounds complex to us, with many skilled people, those problems are solved rapidly. Consider a company that has a central office, branch offices, and stores. Each store monitors its own inventory (sales and stock arrivals), each branch office collects summary information from the stores, and the central office summaries company data. From the company office, you could not tell how many of a certain item is in stock at a particular store, but you would have a report on how many of that item was sold last month. Very carefully designed data bases -- and very complex data base software -- brings information together so that it looks like it is one place.
Currently, cloud storage is mostly disk storage. This means that security is a concern. New media is constantly being developed that is cheaper with more capacity.
You have pretty good questions.
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10/29/15
Nandakumar N.
10/28/15