A disk image, in computing, is a computer file containing the contents and structure of a disk volume or of an entire data storage device, such as a hard disk drive, tape drive, floppy disk, optical disc, or USB flash drive. A disk image is usually made by creating a sector-by-sector copy of the source medium, thereby perfectly replicating the structure and contents of a storage device independent of the file system. Depending on the disk image format, a disk image may span one or more computer files.
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The file format may be an open standard, such as the ISO image format for optical disc images, or a disk image may be unique to a particular software application.
The size of a disk image can be large because it contains the contents of an entire disk. To reduce storage requirements, if an imaging utility is filesystem-aware it can omit copying unused space, and it can compress the used space.
History[edit]
Disk images were originally (in the late 1960s) used for backup and disk cloning of mainframe disk media. The early ones were as small as 5 megabytes and as large as 330 megabytes, and the copy medium was magnetic tape, which ran as large as 200 megabytes per reel.[1] Disk images became much more popular when floppy disk media became popular, where replication or storage of an exact structure was necessary and efficient, especially in the case of copy protected floppy disks.
Uses[edit]
Disk images are used for duplication of optical media including DVDs, Blu-ray discs, etc. It is also used to make perfect clones of hard disks.
A virtual disk may emulate any type of physical drive, such as a hard disk drive, tape drive, key drive, floppy drive, CD/DVD/BD/HD DVD, or a network share among others; and of course, since it is not physical, requires a virtual reader device matched to it (see below). An emulated drive is typically created either in RAM for fast read/write access (known as a RAM disk), or on a hard drive. Typical uses of virtual drives include the mounting of disk images of CDs and DVDs, and the mounting of virtual hard disks for the purpose of on-the-fly disk encryption ('OTFE').
Some operating systems such as Linux[2] and macOS[3] have virtual drive functionality built-in (such as the loop device), while others such as older versions of Microsoft Windows require additional software. Starting from Windows 8, Windows includes native virtual drive functionality.[4][5]
Virtual drives are typically read-only, being used to mount existing disk images which are not modifiable by the drive. However some software provides virtual CD/DVD drives which can produce new disk images; this type of virtual drive goes by a variety of names, including 'virtual burner'.
Enhancement[edit]
Using disk images in a virtual drive allows users to shift data between technologies, for example from CD optical drive to hard disk drive. This may provide advantages such as speed and noise (hard disk drives are typically four or five times faster than optical drives,[6] are quieter, suffer from less wear and tear, and in the case of solid-state drives, are immune to some physical trauma). In addition it may reduce power consumption, since it may allow just one device (a hard disk) to be used instead of two (hard disk plus optical drive).
Virtual drives may also be used as part of emulation of an entire machine (a virtual machine).
Software distribution[edit]
Since the spread of broadband, CD and DVD images have become a common medium for Linux distributions.[2] Applications for macOS are often delivered online as an Apple Disk Image containing a file system that includes the application, documentation for the application, and so on. Online data and bootable recovery CD images are provided for customers of certain commercial software companies.
Disk images may also be used to distribute software across a company network, or for portability (many CD/DVD images can be stored on a hard disk drive). There are several types of software that allow software to be distributed to large numbers of networked machines with littleor no disruption to the user. Some can even be scheduled to update only at night so that machines are not disturbed during business hours. These technologies reduce end-user impact and greatly reduce the time and man-power needed to ensure a secure corporate environment.[7] Efficiency is also increased because there is much less opportunity for human error. Disk images may also be needed to transfer software to machines without a compatible physical disk drive.
For computers running macOS, disk images are the most common file type used for softwaredownloads, typically downloaded with a web browser. The images are typically compressed Apple Disk Image (.dmg suffix) files. They are usually opened by directly mounting them without using a real disk. The advantage compared with some other technologies, such as Zip and RAR archives, is they do not need redundant drive space for the unarchived data.
Software packages for Windows are also sometimes distributed as disk images including ISO images. While Windows versions prior to Windows 7 do not natively support mounting disk images to the files system, several software options are available to do this; see Comparison of disc image software.
Security[edit]
Virtual hard disks are often used in on-the-fly disk encryption ('OTFE') software such as FreeOTFE and TrueCrypt, where an encrypted 'image' of a disk is stored on the computer. When the disk's password is entered, the disk image is 'mounted', and made available as a new volume on the computer. Files written to this virtual drive are written to the encrypted image, and never stored in cleartext.
The process of making a computer disk available for use is called 'mounting', the process of removing it is called 'dismounting' or 'unmounting'; the same terms are used for making an encrypted disk available or unavailable.
Virtualization[edit]
A hard disk image is interpreted by a Virtual Machine Monitor as a system administrator using terms of naming, a hard disk image for a certain Virtual Machine monitor has a specific file.
Hard drive imaging is used in several major application areas:
- Forensic imaging is the process where the entire drive contents are imaged to a file and values are verify the integrity of the image file. Forensic images are acquired with the use of software tools. Some tools have added forensic functionality previously mentioned; it is typically used to replicate the contents of the hard drive for use in another system. This can typically be done by software programs as it only structure are files themselves.
- Data recovery imaging is the process of imaging every single sector on the source drive to another medium from which required files can be retrieved. In data recovery situations, one cannot rely on the integrity of the file structure and therefore a complete sector copy is mandatory to imaging end there though. Forensic images are typically acquired using software tools However, forensic imaging software tools have significantly limited ability to deal with drives that have hard errors which is often the case.
System backup[edit]
Some backup programs only back up user files; boot information and files locked by the operating system, such as those in use at the time of the backup, may not be saved on some operating systems. A disk image contains all files, faithfully replicating all data. For this reason, it is also used for backing up CDs and DVDs.
Files that don't belong to installed programs can usually be backed up with file-based backup software, and this is preferred because file-based backup usually saves more time or space because they never copy unused space (as a bit-identical image does), they usually are capable of incremental backups, and generally have more flexibility. But for files of installed programs, file-based backup solutions may fail to reproduce all necessary characteristics, particularly with Windows systems. For example, in Windows certain registry keys use short filenames, which are sometimes not reproduced by file-based backup, some commercial software uses copy protection that will cause problems if a file is moved to a different disk sector, and file-based backups do not always reproduce metadata such as security attributes. Creating a bit-identical disk image is one way to ensure the system backup will be exactly as the original. Bit-identical images can be made in Linux with dd, available on nearly all live CDs.
Most commercial imaging software is 'user-friendly' and 'automatic' but may not create bit-identical images. These programs have most of the same advantages, except that they may allow restoring to partitions of a different size or file-allocation size, and thus may not put files on the same exact sector. Macbook shortcut close window. Additionally, if they do not support Windows Vista, they may slightly move or realign partitions and thus make Vista unbootable (see Windows Vista startup process).
Rapid deployment of clone systems[edit]
Large enterprises often need to buy or replace new computer systems in large numbers. Installing operating system and programs into each of them one by one requires a lot of time and effort and has a significant possibility of human error. Therefore, system administrators use disk imaging to quickly clone the fully prepared software environment of a reference system. This method saves time and effort and allows administrators to focus on unique distinctions that each system must bear.
There are several types of disk imaging software available that use single instancing technology to reduce the time, bandwidth, and storage required to capture and archive disk images. This makes it possible to rebuild and transferinformation-rich disk images at lightning speeds, which is a significant improvement over the days when programmers spent hours configuring each machine within an organization.[8]
Legacy hardware emulation[edit]
Emulators frequently use disk images to simulate the floppy drive of the computer being emulated. Photoshop cc 2017 software. This is usually simpler to program than accessing a real floppy drive (particularly if the disks are in a format not supported by the host operating system), and allows a large library of software to be managed.
Copy protection circumvention[edit]
A mini image is an optical disc image file in a format that fakes the disk's content to bypass CD/DVD copy protection.
Because they are the full size of the original disk, Mini Images are stored instead. Mini Images are small, on the order of kilobytes, and contain just the information necessary to bypass CD-checks. Therefore; the Mini Image is a form of a No-CD crack, for unlicensed games, and legally backed up games. Mini images do not contain the real data from an image file, just the code that is needed to satisfy the CD-check. They cannot provide CD or DVD backed data to the computer program such as on-disk image or video files.
Creation[edit]
Creating a disk image is achieved with a suitable program. Different disk imaging programs have varying capabilities, and may focus on hard drive imaging (including hard drivebackup, restore and rollout), or optical media imaging (CD/DVD images).
A virtual disk writer or virtual burner is a computer program that emulates an actual disc authoring device such as a CD writer or DVD writer. Instead of writing data to an actual disc, it creates a virtual disk image.[9][10] A virtual burner, by definition, appears as a disc drive in the system with writing capabilities (as opposed to conventional disc authoring programs that can create virtual disk images), thus allowing software that can burn discs to create virtual discs.[11]
File formats[edit]
Utilities[edit]
RawWrite and WinImage are examples of floppy disk image file writer/creator for MS-DOS and Microsoft Windows. They can be used to create raw image files from a floppy disk, and write such image files to a floppy.
In Unix or similar systems the dd program can be used to create disk images, or to write them to a particular disk. It is also possible to mount and access them at block level using a loop device.
Apple Disk Copy can be used on Classic Mac OS and macOS systems to create and write disk image files.
Authoring software for CDs/DVDs such as Nero Burning ROM can generate and load disk images for optical media.
See also[edit]
- ISO image, an archive file of an optical media volume
- Protected Area Run Time Interface Extension Services (PARTIES)
References[edit]
- ^'IBM Mainframe Operating Systems'(PDF). Archived from the original(PDF) on 2014-07-01. Retrieved 2014-06-17.
- ^ ab'Linux ISO Images'. LinuxHelp.net. Archived from the original on 2007-03-02. Retrieved 2007-03-23.
- ^Although macOS's built-in DiskImageMounter software does not emulate a physical drive
- ^'Accessing data in ISO and VHD files'. Building Windows 8 (TechNet Blogs). Microsoft. 30 August 2011. Archived from the original on 19 April 2012. Retrieved 27 April 2012.
- ^'Mount-DiskImage'. Storage Cmdlets (TechNet). Microsoft. Archived from the original on 2017-12-01.
- ^pcguide.com - Access Time
- ^'Software Distribution'. Dell KACE. Archived from the original on 2015-10-03. Retrieved 2015-10-01.
- ^'Disk Imaging'. Dell KACE. Archived from the original on 2015-10-02. Retrieved 2015-10-01.
- ^'Phantom Burner Overview'. Phantombility, Inc. Archived from the original on 19 August 2011. Retrieved 19 July 2011.
- ^'Virtual CD - The original for your PC'. Virtual CD website. H+H Software GmbH. Archived from the original on 24 September 2011. Retrieved 19 July 2011.
- ^'Virtual CD/DVD-Writer Device'. SourceForge. Geeknet, Inc. Archived from the original on 17 February 2011. Retrieved 19 July 2011.
External links[edit]
About SystemRescue
Creating a disk image is achieved with a suitable program. Different disk imaging programs have varying capabilities, and may focus on hard drive imaging (including hard drivebackup, restore and rollout), or optical media imaging (CD/DVD images).
A virtual disk writer or virtual burner is a computer program that emulates an actual disc authoring device such as a CD writer or DVD writer. Instead of writing data to an actual disc, it creates a virtual disk image.[9][10] A virtual burner, by definition, appears as a disc drive in the system with writing capabilities (as opposed to conventional disc authoring programs that can create virtual disk images), thus allowing software that can burn discs to create virtual discs.[11]
File formats[edit]
Utilities[edit]
RawWrite and WinImage are examples of floppy disk image file writer/creator for MS-DOS and Microsoft Windows. They can be used to create raw image files from a floppy disk, and write such image files to a floppy.
In Unix or similar systems the dd program can be used to create disk images, or to write them to a particular disk. It is also possible to mount and access them at block level using a loop device.
Apple Disk Copy can be used on Classic Mac OS and macOS systems to create and write disk image files.
Authoring software for CDs/DVDs such as Nero Burning ROM can generate and load disk images for optical media.
See also[edit]
- ISO image, an archive file of an optical media volume
- Protected Area Run Time Interface Extension Services (PARTIES)
References[edit]
- ^'IBM Mainframe Operating Systems'(PDF). Archived from the original(PDF) on 2014-07-01. Retrieved 2014-06-17.
- ^ ab'Linux ISO Images'. LinuxHelp.net. Archived from the original on 2007-03-02. Retrieved 2007-03-23.
- ^Although macOS's built-in DiskImageMounter software does not emulate a physical drive
- ^'Accessing data in ISO and VHD files'. Building Windows 8 (TechNet Blogs). Microsoft. 30 August 2011. Archived from the original on 19 April 2012. Retrieved 27 April 2012.
- ^'Mount-DiskImage'. Storage Cmdlets (TechNet). Microsoft. Archived from the original on 2017-12-01.
- ^pcguide.com - Access Time
- ^'Software Distribution'. Dell KACE. Archived from the original on 2015-10-03. Retrieved 2015-10-01.
- ^'Disk Imaging'. Dell KACE. Archived from the original on 2015-10-02. Retrieved 2015-10-01.
- ^'Phantom Burner Overview'. Phantombility, Inc. Archived from the original on 19 August 2011. Retrieved 19 July 2011.
- ^'Virtual CD - The original for your PC'. Virtual CD website. H+H Software GmbH. Archived from the original on 24 September 2011. Retrieved 19 July 2011.
- ^'Virtual CD/DVD-Writer Device'. SourceForge. Geeknet, Inc. Archived from the original on 17 February 2011. Retrieved 19 July 2011.
External links[edit]
About SystemRescue
Description: SystemRescue (also known as SystemRescueCd) is a Linuxsystem rescue toolkit available as a bootable medium for administrating orrepairing your system and data after a crash. It aims to provide an easy way tocarry out admin tasks on your computer, such as creating and editing the harddisk partitions. It comes with a lot of Linux system utilitiessuch as GParted, fsarchiver, filesystem tools and basic tools (editors, midnightcommander, network tools). It can be used for both Linuxand windowscomputers, and on desktops as well as servers. This rescue system requires noinstallation as it can be booted from a CD/DVD drive orUSB stick, but it can beinstalled on the hard diskif you wish. The kernel supports all important file systems (ext4, xfs, btrfs,vfat, ntfs), as well as network filesystems such as Samba and NFS.
System and Networking Guides
In addition to the Quick Start Guideand SystemRescue documentation here are other guides:
- Disk Partitioning:Introduction,Attributes,Tools,GPT Disks,How Grub boots,How to repair Grub
- LVM Volume-Manager:Overview,How it works,Booting,Rootfs on LVM,Snapshots and Backups
- Networking on Linux:network configuration,advanced routing,dport routing,load balancing
System Software Examples
Project documentation
This project comes with good documentation. Here are the most important pages:
For the impatient:
- Quick start guide: please read this if this is thefirst time you are using this system recovery cd.
Chapters about basic usage:
Chapters about advanced usage:
System tools included
- GNU Parted: creates, resizes, moves, copies partitions, and filesystems (and more).
- GParted: GUI implementation using the GNU Parted library.
- FSArchiver: flexible archiver that can be used as both system and data recovery software
- ddrescue : Attempts to make a copy of a block device that has hardware errors, optionally filling corresponding bad spots in input with user defined pattern in the copy.
- File systems tools (for Linux and Windows filesystems): format, resize, and debug an existing partition of a hard disk
- Ntfs3g: enables read/write access to MS Windows NTFS partitions.
- Test-disk : tool to check and undelete partition, supports reiserfs, ntfs, fat32, ext3/ext4 and many others
- Memtest: to test the memory of your computer (first thing to test when you have a crash or unexpected problems)
- Rsync: very-efficient and reliable program that can be used for remote backups.
- Network tools (Samba, NFS, ping, nslookup, …): to backup your data across the network
Browse the short system tools page for more details about the most important software included.
Browse the detailed package list for a full list of the packages.
It is possible to make custom versions of the system.For example, you can add your own scripts, make an automatic restoration of thesystem. It is also possible to burn a custom DVD,with SystemRescue and 4GB for your data (backup for example). Read the manualfor more details.
You can use SystemRescue to backup data from an unbootable Windows computer, if youwant to backup the data stored on a Windows computer that cannot boot any more.
It is very easy to install SystemRescue on a USB stick. That is very useful incase you cannot boot from the CD/DVD drive. You just have to copy several files tothe stick and run syslinux. The install process can be done from Linux orWindows. Follow instructions from the manual for more details.
Operating System Software Images
More information about this project
Operating System Software Images
SystemRescue sources can be found onGitLab and these arelicensed under the GPLv3 license.
