Posted 07 May 2006 - 09:17 AM
Posted 07 May 2006 - 09:37 AM
As is typical for disk images, in addition to the data files that are contained in the ISO image, it also contains all the filesystem metadata (boot code, structures, and attributes). All of this information is contained in a single file. These properties make it an attractive alternative to physical media for the distribution of software which requires this additional information as it is simple to retrieve over the Internet.
Some of the common uses include the distribution of operating systems, such as Linux or BSD systems, and LiveCDs.
Most CD/DVD authoring utilities can deal with ISO images: Producing them either by copying the data from existing media or generating new ones from existing files, or using them to create a copy on physical media.
Most operating systems (including Mac OS, BSD, Linux and Windows, with third-party tools) allow these images to be mounted as if they were physical discs, making them somewhat useful as a universal archive format.
Console emulators, such as ePSXe, and many other emulators that read from CD/DVD, are able to run ISO/BIN (and other similar formats) instead of running directly from the CD drive. Better performance is achieved by running an ISO since there is no waiting for the drive to be ready and the hard drive I/O speed is many times faster than the CD/DVD drive
The .iso file is a digital copy of CD contents made this way: the ripper searches for the sectors of the CD that have been used, say 251,000 for instance (there are 330,000 sectors on a 74 min CD and 360,000 sectors on an 80 min CD). Each sector is copied on the .ISO file, one by one, and only 2048 bytes for each sector (only the ones containing the user data) are copied. The .ISO file should then be of size 251,000 x 2048 = 514,408,000 bytes. (It will be slightly bigger if the extractor puts a header on the file, like Nero .NRG files that are .ISO files plus a small file header)
A disk image is a computer file containing the complete contents and structure of a data storage device. The term has been generalized to cover any such file, whether taken from an actual physical storage device or not.
One of the most popular and commonly encountered types of images is a CD/DVD image. In simple terms, a CD/DVD-image is an exact replica of a CD/DVD, whereby all the data is stored in one file for the convenience of its users and as a courtesy to those who prefer CD/DVD-images over compressed archives (.ZIP, .RAR).
Creating a CD/DVD-image is actually very easy, all that is required is an appropriate CD/DVD-imaging program and enough disk space to save the image onto. Some common disk-imaging programs are Alcohol 120%, CDRWin, CloneCD/DVD and Nero Burning ROM for Windows, and Disk Utility and Roxio Toast, for Macintosh. For CDs that contain CD audio (Red Book standard), referred to as multi-track CDs (Data or Audio on the first track, Data or Audio on any subsequent tracks), a CD-image is required, as analog CD audio cannot be copied directly via the Windows interface.
An ordinary backup only backs up the files it can access; boot information, and files locked by an operating system or being changed at the time, may not be saved. A disk image contains all these, and faithfully replicates the data, so it is commonly used for backing up disks with operating systems, or bootable CD/DVDs.
Posted 07 May 2006 - 09:41 AM
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