Naked Science Forum

Non Life Sciences => Geek Speak => Topic started by: Chemistry4me on 26/01/2009 01:28:24

Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Chemistry4me on 26/01/2009 01:28:24
Where does the information 'go' after it has been permanently deleted on a computer?  [???] [???] I have no idea  [???] Can you tell me?  [:)]
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Madidus_Scientia on 26/01/2009 02:16:04
don't think of it as going somewhere, think of it becoming different information. say you have the information 1010101010 on a hard drive, and you delete it and it becomes 0000000000. It's still data, but it doesn't mean anything.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Chemistry4me on 26/01/2009 03:59:30
Hmmm... so that's how it works.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Chemistry4me on 26/01/2009 04:05:02
The stuff in your recycle bin isn't really deleted is it? Not until you permanently delete it?
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Madidus_Scientia on 26/01/2009 04:56:28
No, and even when you empty the recycle bin the data usually remains there until it is overwritten with new data, your OS basically just flags the chunk of data that was the deleted file as "not there". Its alot faster for the hard drive to do this than to run over every byte of data and reset it.

You can use software to recover this data if you get to it before it's overwritten.

Title: Where does the information 'go' after it has been deleted on a computer?
Post by: RD on 26/01/2009 05:21:58
You can use software to recover this data if you get to it before it's overwritten.

and shredder software to destroy the info permanently,
 e.g. if you were selling your computer and sensibly wished to erase all your data from it.

Shredding is irreversible so think very carefully before doing it.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: nicephotog on 27/01/2009 06:55:22
In UNIX only the "position lookup" on the FAT or Journalising 'file allocation table' is deleted of its file parts starts and ends positions, that's called unlinking hence the "unlink" command. In windows it also overwrites the used FAT byte sized sectors.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Chemistry4me on 27/01/2009 06:57:18
Could you please put that in simple English? [:I][:I]
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: LeeE on 27/01/2009 13:58:27
Unix (and unix-like systems such as Linux) use inode based filesystems, not FAT based filesystems.  NTFS is not generally regarded as a FAT filesystem either.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Don_1 on 27/01/2009 14:20:28
Never mind 'where does information go after it has been deleted', I would like to know where the hell it goes before in some cases!!!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.freesmileys.org%2Fsmileys%2Fsmiley-confused013.gif&hash=396386a856152a890252526964cc44dd) (http://www.freesmileys.org)
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: LeeE on 27/01/2009 14:26:03
Never mind 'where does information go after it has been deleted', I would like to know where the hell it goes before in some cases!!!
(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.freesmileys.org%2Fsmileys%2Fsmiley-confused013.gif&hash=396386a856152a890252526964cc44dd) (http://www.freesmileys.org)

Now that is a good question  [;D]

An old computing haiku:

A file that big?
It might be very useful
But now it is gone
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Don_1 on 27/01/2009 14:38:45
User Error, Windows was not shut down properly last time.

I bloody know, because you bloody froze!!!

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.freesmileys.org%2Fsmileys%2Fsmiley-computer012.gif&hash=eef52b7fab7e178431705b29d072ec06) (http://www.freesmileys.org)
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: LeeE on 27/01/2009 14:45:37
I think the funniest Windows error message I've seen was the one that concluded with:  "The error was: no error"

A bit of denial going on there, methinks.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: LeeE on 27/01/2009 14:51:13
And then there's:

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.boreme.com%2Fmedia%2Fyr2002%2Fwindaz.gif&hash=3a751a87d15b89d085b1a52da03838c1)
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: wolfekeeper on 27/01/2009 19:00:32
FWIW the answer to the question is that as you delete the information the information gets written to zero. When that happens it takes a minimal amount of energy to do that (to change the ones to zero, the zeros don't take any particular energy in principle), and that produces a certain amount of heat.

So, basically, it increases the 'entropy' of the world and generates a bit of heat.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Don_1 on 28/01/2009 09:19:52
LeeE, that's fantastic.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Chemistry4me on 28/01/2009 09:29:06
It really its!
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: yor_on on 28/01/2009 15:48:35
The only sure way to treat your hard disk to keep quiet, is with a hammer.

there are examples on hard disks that been owerwritten nine times that still squeaked.

Join the don't trust your HD movement.
Buy a Suzuki:)
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: DoctorBeaver on 28/01/2009 17:58:00
yor-on - the only totally safe way is to melt it.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: nicephotog on 29/01/2009 23:09:33
There is a GNU software for keys and signatures in email messages  called PGP(Pretty Good Privacy), it has a "shredder" bin system or command and it overwrites the track sectors where the file chunk(s) is/are placed 32 times. Truthfully to retrieve overwritten tracks on the hard-discs' disc platters requires removing the disc platters and placing them in a special reader machine. Edges of the track from only a few overwrites can(could) yield most of the sets of information from the last sets of overwrite.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Vern on 06/02/2009 22:13:04
The files are stored on disk drives in little short strips called sectors. Usually a file will use several sectors. The beginning and end of each little strip has an ID number. There is a master file on each drive that stores the numbers of all the little strips that contain data and the names of the files that the data goes to. When you delete a file, you just remove the stored numbers in the master file so that the little strips can be re-used. Until they are re-used, the data is still there on the drive.

Edit: I don't know exactly how NTFS works but it seems to divide a drive into tracks that circle around like the grooves on a phonograph record. Each track is divided up into a bunch of sectors. When a file is stored, it gets a list of available sectors from a master file on the drive. It then writes the file into the sectors. The sectors need not be all in a row. The file may be split up into sectors all over the drive.

The master file is kept in RAM, and only written back onto the drive when time is available. Also the files themselves are not written back to the drive instantly. That's why when you get a hard shutdown, you can get into trouble. The stuff in RAM that was supposed to be written back to the drive is lost. Then the master file on the drive might have the wrong numbers for the locations of the data on the drive.

I think it works that way [:)]
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: LeeE on 07/02/2009 15:06:48
...The master file is kept in RAM, and only written back onto the drive when time is available. Also the files themselves are not written back to the drive instantly. That's why when you get a hard shutdown, you can get into trouble. The stuff in RAM that was supposed to be written back to the drive is lost. Then the master file on the drive might have the wrong numbers for the locations of the data on the drive.

I think it works that way [:)]

What you're talking about there is write-caching and while it can deliver some performance benefits, it's generally a bad idea and is not often used, precisely because of the reasons you give.  Even without write-caching though, it's still possible to get a crash during write procedures and this is where you'll sometimes see disk recovery being required on restart.

Write-caching is not the same as working on a file in an application; with most applications, such as editing a word-procesing document in something like Word etc, you'll loose anything that you haven't saved, or which hasn't been auto-saved, because the system has not been asked to write the data back to disk.  I do fondly remember the DEC VAX VMS editor, which was journalised, and which wouldn't loose anything since the last keystroke in a crash; every keystroke was logged to the journal file, and the screen was updated to show the effect of the keystroke, but the keystrokes weren't actually applied to the file until you saved it.  As a consequence, if the system crashed the original file would still be in it's unedited state and the keystroke journal, which may have been left open, would have simply been closed by the filesystem check on restart and then be re-applied when you restarted the editor on the original file again.  You could optionally watch all your keystrokes being re-applied when restarting the editor, which was quite entertaining.

I can't understand why this scheme is not used with all software these days; the overhead is tiny.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Vern on 07/02/2009 15:23:19
I think write-caching is used all the time. Also read-caching, if you want to call it that. An operating system can play out of RAM much faster than play from disk. I think the speed advantage is about two orders of magnitude better with caching.

I know in Linux and I think in Vista, a paging method is used where applications page themselves into RAM only as required. So that if a particular part of the AP is not needed it may never even be loaded into RAM.

Edit: After doing a little research I find that this might be user controllable. Maybe I'm living in the past and just haven't caught up to speed [:)]

Quote
Enabling or Disabling the Disk Write Caching

   1. Right-click My Computer, and then click Properties.
   2. Click the Hardware tab.
   3. Click Device Manager.
   4. Click the plus sign (+) next to the Disk Drives branch to expand it.
   5. Right-click the drive on which you want to enable or disable disk write caching, and then click Properties.
   6. Click the Disk Properties tab.
   7. Click to select or clear the Write Cache Enabled check box as appropriate.
   8. Click OK.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: LeeE on 07/02/2009 16:18:08
Read-caching is very common, it's normal in fact, but that's because there are very few problems associated with it.  The only time I can think of right now, when it can be a bad idea, is with multi-user transactional databases, where in some circumstances, read caching might lead to stale data being read.  This is largely taken in to consideration in the design of the DB engine and caching policies though and rarely has to be considered by the application designer.

As you point out, software can run more quickly from from RAM than disk, so in most systems any unused RAM will be used as cache; on the system I'm using right now 56% of RAM is being used as cache.

Although the CPUs page memory in and out, I think you're really referring to swap space here, which is where RAM contents, both system and application data and code (obviously, it make no sense to swap cache data), is written to disk when RAM usage exceeds RAM capacity, and yes, RAM contents that are not used will be written to swap if the RAM they occupy is required for something else.  Once you've started using swap space though, because you've filled the RAM with software and data, the amount of RAM used for cache will be tiny.  As the system I'm writing this on is using 56% of RAM for cache, you'll be able to guess that I'm currently using no swap space at all (this isn't because I've got lots of RAM - just 512MB in fact - but because I'm using Linux and not windows.  On an identically spec'ed system that dual boots XP, XP uses around 280 MB swap after start-up, and that's without running an SQL DB server, which I do on the Linux boxes)

Write-caching though, like I said, comes with obvious dangers and in general is a bad idea.  Windows may allow you to enable it but I wouldn't recommend it.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: yor_on on 28/02/2009 14:09:31
Nice explanation LeeE.

Thats what I like with Linux too. It uses its 'resources' so efficiently.
And with a journaling system like Reiser FS, it seems very hard to lose any data due to loss of electricity etc. I've never had a situation where Linux couldn't recreate the 'information' on the harddisk. On the other hand I find XP pro quite stable too. I don't really have a explanation for why I use XP privately instead, habit I supose :).

It's all this with the constant 'speeding up' of computers that hides the benefits of Linux. You won't notice the performance difference when using it privately, but if I want to use a OS 'professionally' then it is Linux that gets my vote, not XP, how much I ever may like its simple and intuitive interface.

How many of you use a 'dual boot' privately. I do, and I know that Vern do too:)
It may be rather geeky perhaps?
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Karen W. on 02/03/2009 15:00:14

So say someone  wants to keep their information to themselves and very private... but wishes to put info on anther computer and give old computer away like was suggested ..or sell it...... can the info be deleted to the point to where the most skilled computer analysts  could not retrieve info...and still be left witha fully functional Harddrive?

What if you wiped the hard drive? Would the info still be there ling in wait for a specialist to hook it up to somethging and retrieve all your personal info even though you wiped the hard drive?
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Madidus_Scientia on 02/03/2009 15:49:29
I reckon if you formatted the drive, filled it with junk data (just put like 1000 copies of a largish non-sensitive file onto it) and then formatted it again I don't think anyone would get any data off it.

There's probably programs that will do this for you.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: Karen W. on 02/03/2009 15:59:53
Thats Interesting...thanks.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: MonikaS on 02/03/2009 18:40:23

So say someone  wants to keep their information to themselves and very private... but wishes to put info on anther computer and give old computer away like was suggested ..or sell it...... can the info be deleted to the point to where the most skilled computer analysts  could not retrieve info...and still be left witha fully functional Harddrive?

What if you wiped the hard drive? Would the info still be there ling in wait for a specialist to hook it up to somethging and retrieve all your personal info even though you wiped the hard drive?

Yes you can do that. For normal security standards MSs way of doing it is enough. But even with that method it is possible to recover some data.

There are special programs who achieve an even higher standard of security.
Here's one of those. (http://the-undelete.com/wipe_remove_delete_erase.php) It won't work for a computer with only one disk, but is great for deleting external disks or USB sticks.
Here's another one. (http://cmrr.ucsd.edu/people/Hughes/SecureErase.shtml) You boot from a floppy or CD or USB Stick and this DOS based utility erases your harddisk. I've used a similar program which is only available in German to sanitize a whole bunch of computers for a company. They wanted to give them to a charity, but had some sensitive information stored on them.
Title: Where does the information 'go' after it has been deleted on a computer?
Post by: syhprum on 02/03/2009 18:54:24
I use dual boot between XP and Windows 7, its horses for courses XP is slower but I like the GUI better.
I have done my best to make Windows 7 look like XP but I seldom find it has any significant advantage over XP.
I notice with all the updates you get for XP it begins to behave like Windows 7 in some ways.