ISO image
| ISO image | |
|---|---|
|
|
| File extension : |
.cdr, .dvdr, .img, .iso
|
| MIME type : | application / x-cd-image , application / x-iso-image , application / x-iso9660-image |
| Type: | Memory dump |
| Container for: | ISO 9660 , UDF |
| Standard (s) : | 1: 1 copy of ISO 9660 , UDF (ISO 13346) |
ISO image ( English ISO image ) is the name for a computer - file that a memory dump of the file system of a CD or DVD contains, in the format ISO 9660 or 13346 is structured.
The file system is copied unchanged when an ISO image is created (1: 1 copy), which means that authorizations and other metadata remain unchanged.
The standard ISO 9660 defines a file system for CDs or DVDs , and its successor ISO 13346 - better known as Universal Disk Format - in addition to DVD ± R / W , DVD-RAM and BD-R / E .
Implementation options
An identical image of a CD or DVD is created either directly on the (target) medium (“ on the fly ”) or in the form of an “ISO file”.
"On-the-fly"
The creation of an ISO image "on-the-fly" takes place by means of two drives - one readable and one writable. The reading of the original from the reader and the writing in the burner take place synchronously (analogous to the procedure for old audio cassettes ).
The reader must be sufficiently powerful (at least twice as fast as the burner). The data carrier must not show any damage so that the constant data stream required for writing is guaranteed.
Such a 1: 1 process results in (almost) exactly the same CD or DVD. In the strict sense, the term “almost the same” must be used, because almost every burning process is subject to errors. It is also possible that there are defects on the source CD due to individual scratches or dust and the like. However, if the number of errors does not exceed a critical level, the space available between the pure user data is sufficient to write information for error correction or to recover the user data from it without errors. In addition to the division into data blocks, the space is also used to accommodate additional bits that allow the reconstruction of erroneous data ( forward error correction ) or at least reveal whether an error has occurred ( checksum ). In this way, the errors that have arisen can and must be "calculated out", so to speak, in each subsequent reading process.
ISO file
There are several advantages to using an ISO file:
- The creation of an ISO file is not time-critical like the burning process on a blank disc ; This means that copies can also be made if - to a certain extent - the legibility of the original is restricted.
- The creation of an ISO file is particularly useful for multiple copies: the original only needs to be read in once - during the burn process, the data on the hard disk is accessed for all copies and not the data of the original again and again.
- If there is only one device (burner), creating an ISO image is generally the only way to create a copy.
- An ISO image is also advantageous when making copies if you have to get to the original data on a CD quickly despite a large spatial distance (via remote data transmission ).
ISO images in practice
For example, a downloaded ISO image can be opened with tools such as IsoBuster or 7-Zip . Almost every burning program can burn an ISO image onto a medium. From Windows 7 onwards, a corresponding burning program is included with Windows ( Windows burner for disk images ). It is important that you do not burn the ISO file as a file on a medium, otherwise you still need a program to open the file and the medium is also not bootable .
An ISO image can also be transferred to a USB memory stick, which can then be booted in the same way as the CD / DVD from which the image originates. Burning programs for transferring onto a CD / DVD are often not able to write to a USB memory stick. However, this functionality is mostly offered by programs that can generate a data carrier image.
With a virtual drive or a " loop device " it is possible to mount an ISO image : The contents are then accessible in the file system; The original or a copy of the data carrier is then no longer necessary, and neither is a corresponding drive.
In the case of commercial CD-ROMs / DVDs, for example computer games , the ability to create ISO images is often impaired by copy protection procedures . Some computer games check whether a virtual drive is installed and will not start if this is the case.