Delete (file)

As delete or remove (English delete or erase ) is in the information technology and computer science in general deleting data referred. A special case is the deletion of files .

Depending on the storage medium , the storage form of the file, the operating system and the file system under which the file is managed, different variants and levels of deletion can be used, for example only the so-called logical and physical deletion .

To understand the processes involved in deletion, a distinction can be made between the file as a logical data unit and its content. The latter can u after deletion. It may still exist in the data memory while the file is considered deleted as such.

Basic forms of deletion for files in file systems

Nowadays files are mainly kept in so-called file systems . The information about the files ( metadata ) is kept in special directories , the data itself is stored separately, possibly in many individual fragments . The individual data blocks can often be accessed directly . The actions to save the data (read, write, change, delete) are mostly carried out using sub-functions of the operating system for file management or via a database system . Several files can be combined in a file directory, which can itself be part of a higher-level directory. For details, see the main file system article .

The following basic forms can be distinguished for deleting such files:

Deleting files in the 'Recycle Bin'

→ Main article : "Information technology" in the article Trash

In many graphical user interfaces , when files are deleted by the user, they are initially only moved to a special folder - for example called "Recycle Bin"; Example see. They are temporarily stored there and can be restored under their original file name without data loss; Example see. As a rule, entire folders (with several files and subdirectories) can be deleted in this way. These files / objects are only removed from the file directory and thus “logically deleted” using the “Empty” recycle bin function (see below).

In some interfaces (e.g. Windows or KDE ) the recycle bin function can be switched on or off manually. It is also possible to "logically" delete files and folders (instead of going to the recycle bin) by pressing the Shift key while deleting (via the menu or the delete key).

Delete functions in command line-oriented interfaces usually do not support the 'trash can' function.

Logical deletion

By a file system are files deleted by its entry (see details from the file directory from Hard Link ) and the current location of the data is considered, rewritable out '. This type of erase is known as logical erase . The data itself is then still on the data carrier; the storage spaces previously occupied by them are only overwritten when they are needed to save other data, possibly for different files. Up to this point in time, they can be restored through the use of special programs , if necessary only partially.

Physical erasure

With physical deletion , also known as secure deletion , the storage space of former files (which was marked as 'free' during logical deletion) is overwritten one or more times with specific bit combinations. This means that the previous data can no longer be evaluated or can only be evaluated with considerable technical (and therefore financial) effort .

However, this is not a single file action and does not occur when a single file is deleted. Rather, it is a measure to increase data security or data protection , which is intended to prevent or make more difficult the reconstruction of the old, actually deleted data.

For magnetic hard drives , there are deleting special programs, for example for this kind Wipe or Eraser .

The VSITR standard ( classified IT guidelines ) of the German Federal Office for Information Security (BSI) has prescribed a one-off overwriting for 'normal security requirements' for several years.

Differences depending on the storage medium

In the case of other storage media managed via file systems (e.g. floppy disk , USB stick , SD card , SSD , CD and DVD, etc.), the aforementioned methods for deleting files are sometimes not used or not used in the manner described for various reasons. Examples of such differences:

• The 'recycle bin function' is not available when deleting or is deactivated.
• Physical deletion does not take place or is implemented using other technical processes than overwriting. See also main article Secure Erase or details on 'Overwrite' in Solid State Media .

Reasons for deleting files

In general, the reason for deleting files is that they are no longer required on the respective data carrier. In detail, for example, the following facts can be the cause:

• The file has been copied / archived (possibly on a different data carrier) and can be removed from the current drive. Example: The photo files from old years.
• The file is a ' backup file ' whose predefined backup duration or number of backup generations has been exceeded.
• The user no longer needs this file. Example: A text file that is no longer relevant or a saved photo. Possibly. the file was only created temporarily, for example as a screenshot from a website.
• Incorrect content was found for a file (e.g. before it was processed) ; it will be deleted and redeployed.
• A new version is created for the file , the old one is no longer required. Delete the old file before saving the new one, alternatively overwrite the old file, resp. their content; mostly automatically.
• The file is one of several files in a given overall context that is no longer relevant. Here deletion of several files, possibly entire directories including content, e.g. B. Data from application software that is no longer used .
• A file can also be accidentally deleted. Their recovery requires the availability of suitable backup data - e.g. B. in the 'recycle bin' or on other backup media.
• The file was uploaded to a cloud or to a server on the Internet and should or must no longer be accessible in the corresponding network at a certain point in time .

Technical tools for deleting files

Files can be deleted operationally in different ways, sometimes explicitly initiated by a user , sometimes implicitly in the execution of any program:

• Via a file manager , for example in a graphical user interface using its menu functions or the Entfbutton;
• As a delete command in a command line-oriented user interface; through defined commands (as rmwith Unixoid operating systems or delor erasewith Windows );
• As functionality in an application or system program : For example, a word processing program can delete an existing old file (version) when / before 'saving'. Or when installing software, the files of the old software version can be deleted.
• Deletion by the file management system itself; z. B. when the number of intended backup generations is exceeded (for details see GDG );
• Emptying the recycle bin , as the second stage of deletion, leads to the logical deletion of the affected files and later re-use of the free space.
• Through physical (secure) erasure using special eraser software ; the free storage space (former files) is overwritten with special characters.
• A service provider is commissioned (for a fee) to delete data on the Internet.

Special features when deleting

Files stored redundantly or distributed

Files from which further copies, e.g. B. Backup copies exist or that were otherwise transferred to a non-local memory (e.g. to a server) are usually stored in several places. It is usually not possible for the user to locate and delete these copies. Whether the copies will ever be deleted depends on e.g. B. on whether old backups will be overwritten by the rotation scheme at some point .

Implicit deletion when replacing file contents

An implicit variant of the deletion is when replacing a file with a different / new content instead. Since the previous content of the file no longer exists, the file is not 'deleted', but its old content. The file then contains a new content - whereby the old file content will mostly only be 'logically deleted'.

Delete files on other media

The term “file” is often and predominantly associated with storage on mass storage media , such as hard drives or flash memories , including solid-state drives , USB sticks or SD cards. However, files are and have been kept on other storage media and it must also be possible to delete or eliminate these files. In the following, therefore, the 'deletion' from these data carriers is briefly explained:

• Magnetic tape : A data carrier usually contained / contains only one file. Erasing is practiced by releasing the data carrier for other purposes to write to; the file is then 'logically no longer existent'. Alternatively, a magnetic tape can be overwritten with blank information - corresponds to the 'physical erasure' of disks. With multivolume tapes, individual files can be 'removed' by selectively copying the remaining files and then releasing / deleting the original tape.
• Magnetic tape cassette : These data carriers were often only used for data acquisition and were then reused after the data had been read or processed. In the case of digital recordings, prior - physical - deletion was not necessary; in order to actually destroy the data, the cassette had to be demagnetized with an erase head .
• Punch card : Files exist (s) in the form of stacks of punch cards. The 'deletion' takes place by removing it from the card archives, physical deletion by destroying / recycling the punch cards.
• Punched tape : essentially like punched cards. Often individual sections of the strip were cut out, the rest glued together, possibly copied onto a new strip and processed again in this way.
• CD-RW / DVD-RW: The entire data carrier can be erased and rewritten.
• CD-R / DVD-R: If further sessions can be attached, i. H. the CD / DVD has not yet been finalized, files can be logically deleted by not entering them in the table of contents of a further session. Physically, the files can only be deleted by destroying the data carrier.
• CD / DVD (not RW): Files cannot be deleted, they are eliminated by removing / destroying the entire data carrier (see also Compact Disc #Destructuring data ).

literature

• Clear. In: Brockhaus-Fachlexikon Computer und Informationstechnologie. 2003, ISBN 3-7653-0251-1 , p. 448.
• Clear. In: Computer Lexicon specialist dictionary. Microsoft Press, 2003, ISBN 3-86063-896-3 , pp. 545 f.

Individual evidence

1. ↑ Deleting objects in the recycle bin , Oracle
2. ↑ Recovering Files from the Recycle Bin , Windows
3. ↑ Data security ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. - Page from the Hessian data protection officer , dated December 31, 1992; see section 16.1.3.1 "Logical deletion" 
4. ↑ Data security ( Memento of the original from March 4, 2016 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. - Page from the Hessian data protection officer , dated December 31, 1992; see section 16.1.3.2 "Physical deletion" 
5. ↑ Archived copy ( memento of the original from June 30, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
6. ↑ ^{a b Erasing} data on the Internet: How to remove photos and texts , test.de, February 6, 2015, accessed on February 19, 2015