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A disk image is a snapshot of a storage device's structure and data typically stored in one or more computer files on another storage device.^[1]^[2] Traditionally, disk images were bit-by-bit copies of every sector on a hard disk often created for digital forensic purposes, but it is now common to only copy allocated data to reduce storage space.^[3]^[4] Compression and deduplication are commonly used to reduce the size of the image file set.^[3]^[5] Disk imaging is done for a variety of purposes including digital forensics^[6]^[2], cloud computing^[7], system administration^[8], as part of a backup strategy,^[1] and legacy emulation as part of a digital preservation strategy.^[9] Disk images can be made in a variety of formats depending on the purpose. Virtual disk images (such as VHD and VMDK) are intended to be used for cloud computing^[10]^[11], ISO images are intended to emulate optical media^[12] and RAW disk images are used for forensic purposes.^[2] Proprietary formats are typically used by disk imaging software. Despite the benefits of disk imaging the storage costs can be high^[3], management can be difficult^[6] and they can be time consuming to create.^[13]^[9]

Background

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.^[14] 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.

Disk image creation is called disk imaging and is often time consuming, even with a fast computer, because the entire disk must be copied.^[13] Typically, disk imaging requires a third party disk imaging program or backup software. The software required varies according to the type of disk image that needs to be created. For example, RawWrite and WinImage create floppy disk image files for MS-DOS and Microsoft Windows.^[15]^[16] In Unix or similar systems the dd program can be used to create raw disk images.^[2] 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. 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.^[17]^[18] 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.^[19]

Uses

Digital forensics

Forensic imaging is the process of creating a bit-by-bit copy of the data on the drive, including files, metadata, volume information, filesystems and their structure.^[2] Often, these images are also hashed to verify their integrity and that they have not been altered since being created. Unlike disk imaging for other purposes, digital forensic applications take a bit-by-bit copy to ensure forensic soundness. The purposes of imaging the disk is to not only discover evidence preserved in digital information but also to examine the drive to gather clues of how the crime was committed.

Cloud computing

In cloud computing, creating a disk image of optical media or a hard disk drive is especially useful. Virtual machines emulate a CD/DVD drive by reading an ISO image. This can also be faster than reading from the physical optical medium.^[20] Further, there are less issues with wear and tear. A hard disk drive or solid-state drive in a virtual machine is implemented as a disk image, stored either as a collection of files, collectively called a split flat file, where each one is typically 2GB in size, or as a single, large monolithic flat file. Virtual machines treat the image as a physical disk.

System administration

Rapid deployment of clone systems

Educational institutions and businesses can often need to buy or replace computer systems in large numbers. Disk imaging is commonly used to deploy the same configuration across workstations.^[8] Typically, disk imaging software (such as Ghost or Clonezilla) is used to make an image of a completely configured system.^[21] This image is then written to a computer's hard disk which is sometimes described as restoring an image.^[22] This restoration is sometimes done over a computer network using multicasting or BitTorrent to devices that need to have their configuration restored.^[23]^[22] This reduces the need to maintain and update individual systems manually. Imaging is also easier than automated setup methods for deploying a computer because an administrator does need to have knowledge of the prior configuration to copy it.^[22] Disk imaging requires for all devices to be identical and provides no flexibility in adjusting the configuration.

Network-based image deployment typically uses a PXE server to boot a minimal operating system over the network that contains the necessary components to image or restore storage media in a computer.^[23] This is usually used in conjunction with a DHCP server to automate the configuration of network parameters including IP addresses. Typically, multicasting, broadcasting or unicasting is used to restore an image to many computers at a time but these approaches do not work well if one or more computers experience a problem such as UDP packet loss.^[22] As a result, some imaging solutions instead use the BitTorret protocol to transfer the data.

Backup strategy

A disk image contains all files, faithfully replicating all data, including file attributes and the file fragmentation state. For this reason, it is also used for backing up optical media (CDs and DVDs, etc.), and allows the exact and efficient recovery after experimenting with modifications to a system or virtual machine. Typically, disk imaging can be used to quickly restore an entire system to an operational state after a disaster.^[24]

Digital preservation

Libraries and museums are typically required to archive and digitally preserve information without altering it in any matter.^[9]^[25] Emulators frequently use disk images to emulate floppy disks that have been preserved. 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. Emulation also allows existing disk images to be put into a usable form even though the data contained in the image is no longer readable without emulation.^[12]

Limitations

Disk images can sometimes be slower than reading from the disk directly because of a performance overhead.^[3] Other limitations can be the lack of access to software required to read the contents of the image. For example, prior to Windows 8, third party software was required to mount disk images.^[26]^[27] Disk imaging is time consuming and the space requirements are high. When imaging multiple computers with only minor differences, much data is duplicated unnecessarily, wasting space.^[3]

Speed and failure

Disk imaging can be slow, especially for older storage devices. A typical 4.7 GB DVD can take an average of 18 minutes to duplicate.^[9] Floppy disks read and write much slower than hard disks. Therefore, despite their small size, it can take several minutes to copy a single disk. In some cases, disk imaging can fail due to bad sectors or physical wear and tear on the source device.^[12] Utilities such as dd are not designed to recognize or cope with failures. Therefore, any failure results in being unable to create an image of the drive.^[25]

References

^ ^a ^b "Disk Imaging as a Backup Tool for Digital Objects". Conservation of Time-Based Media Art: 204–222. 2022-11-02. doi:10.4324/9781003034865-17.
^ ^a ^b ^c ^d ^e Woods, Kam; Lee, Christopher A.; Garfinkel, Simson (2011-06-13). "Extending digital repository architectures to support disk image preservation and access". Proceedings of the 11th annual international ACM/IEEE joint conference on Digital libraries. JCDL '11. New York, NY, USA: Association for Computing Machinery: 57–66. doi:10.1145/1998076.1998088. ISBN 978-1-4503-0744-4.
^ ^a ^b ^c ^d ^e Pullakandam, R., Lin, X., Hibler, M., Eide, E., & Ricci, R. High-performance Disk Imaging With Deduplicated Storage.
^ Kävrestad, Joakim (2017), Kävrestad, Joakim (ed.), "Vocabulary", Guide to Digital Forensics: A Concise and Practical Introduction, Cham: Springer International Publishing, pp. 125–126, doi:10.1007/978-3-319-67450-6_12, ISBN 978-3-319-67450-6, retrieved 2023-01-12
^ Lee, Sang Su; Kyong, Un Sung; Hong, Do Won (2008). "A high speed disk imaging system". 2008 IEEE International Symposium on Consumer Electronics: 1–3. doi:10.1109/ISCE.2008.4559553.
^ ^a ^b Garfinkel, Simson L. (2009). "Automating Disk Forensic Processing with SleuthKit, XML and Python". 2009 Fourth International IEEE Workshop on Systematic Approaches to Digital Forensic Engineering: 73–84. doi:10.1109/SADFE.2009.12.
^ Kazim, Muhammad; Masood, Rahat; Shibli, Muhammad Awais (2013-11-26). "Securing the virtual machine images in cloud computing". Proceedings of the 6th International Conference on Security of Information and Networks. SIN '13. New York, NY, USA: Association for Computing Machinery: 425–428. doi:10.1145/2523514.2523576. ISBN 978-1-4503-2498-4.
^ ^a ^b Blackham, N., & Higby, C., & Bailey, M. (2004, June), Re Imaging Computers For Multipurpose Labs , 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--14125
^ ^a ^b ^c ^d Day, Michael; Pennock, Maureen; May, Peter; Davies, Kevin; Whibley, Simon; Kimura, Akiko; Halvarsson, Edith (2016). "The preservation of disk-based content at the British Library: Lessons from the Flashback project". Alexandria: The Journal of National and International Library and Information Issues. 26 (3): 216–234. doi:10.1177/0955749016669775. ISSN 0955-7490.
^ Arunkumar, G.; Venkataraman., Neelanarayanan (2015-01-01). "A Novel Approach to Address Interoperability Concern in Cloud Computing". Procedia Computer Science. Big Data, Cloud and Computing Challenges. 50: 554–559. doi:10.1016/j.procs.2015.04.083. ISSN 1877-0509.
^ Barrowclough, John Patrick; Asif, Rameez (2018-06-11). "Securing Cloud Hypervisors: A Survey of the Threats, Vulnerabilities, and Countermeasures". Security and Communication Networks. 2018: e1681908. doi:10.1155/2018/1681908. ISSN 1939-0114.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ ^a ^b ^c Colloton, E., Farbowitz, J., Fortunato, F., & Gil, C. (2019). Towards Best Practices In Disk Imaging: A Cross-Institutional Approach. Electronic Media Review, 2019-2020.
^ ^a ^b Stewart, Dawid; Arvidsson, Alex (2022). Need for speed : A study of the speed of forensic disk imaging tools.
^ "IBM Mainframe Operating Systems" (PDF). Archived from the original (PDF) on 2014-07-01. Retrieved 2014-06-17.
^ McCune, Mike (2000). Integrating Linux and Windows. Prentice Hall Professional. ISBN 978-0-13-030670-8.
^ Li, Hongwei; Yin, Changhong; Xu, Yaping; Guo, Qingjun (2010). "Construction of the Practical Teaching System on Operating Systems Course". 2010 Second International Workshop on Education Technology and Computer Science. 1: 405–408. doi:10.1109/ETCS.2010.184.
^ "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.
^ pcguide.com - Access Time
^ Bowling, Jeramiah (2011-01-01). "Clonezilla: build, clone, repeat". Linux Journal. 2011 (201): 6:6. ISSN 1075-3583.
^ ^a ^b ^c ^d Shiau, Steven J. H.; Huang, Yu-Chiang; Tsai, Yu-Chin; Sun, Chen-Kai; Yen, Ching-Hsuan; Huang, Chi-Yo (2021). "A BitTorrent Mechanism-Based Solution for Massive System Deployment". IEEE Access. 9: 21043–21058. doi:10.1109/ACCESS.2021.3052525. ISSN 2169-3536.
^ ^a ^b Shiau, Steven J. H.; Sun, Chen-Kai; Tsai, Yu-Chin; Juang, Jer-Nan; Huang, Chi-Yo (2018). "The Design and Implementation of a Novel Open Source Massive Deployment System". Applied Sciences. 8 (6): 965. doi:10.3390/app8060965. ISSN 2076-3417.{{cite journal}}: CS1 maint: unflagged free DOI (link)
^ "Fast, Scalable Disk Imaging with Frisbee". www.cs.utah.edu. Retrieved 2023-01-12.
^ ^a ^b Durno, John; Trofimchuk, Jerry (2015-01-21). "Digital forensics on a shoestring: a case study from the University of Victoria". The Code4Lib Journal (27). ISSN 1940-5758.
^ "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.

External links

Software repository including RAWRITE2

[:0-1] "Disk Imaging as a Backup Tool for Digital Objects". Conservation of Time-Based Media Art: 204–222. 2022-11-02. doi:10.4324/9781003034865-17.

[:3-2] Woods, Kam; Lee, Christopher A.; Garfinkel, Simson (2011-06-13). "Extending digital repository architectures to support disk image preservation and access". Proceedings of the 11th annual international ACM/IEEE joint conference on Digital libraries. JCDL '11. New York, NY, USA: Association for Computing Machinery: 57–66. doi:10.1145/1998076.1998088. ISBN 978-1-4503-0744-4.

[:1-3] Pullakandam, R., Lin, X., Hibler, M., Eide, E., & Ricci, R. High-performance Disk Imaging With Deduplicated Storage.

[4] Kävrestad, Joakim (2017), Kävrestad, Joakim (ed.), "Vocabulary", Guide to Digital Forensics: A Concise and Practical Introduction, Cham: Springer International Publishing, pp. 125–126, doi:10.1007/978-3-319-67450-6_12, ISBN 978-3-319-67450-6, retrieved 2023-01-12

[5] Lee, Sang Su; Kyong, Un Sung; Hong, Do Won (2008). "A high speed disk imaging system". 2008 IEEE International Symposium on Consumer Electronics: 1–3. doi:10.1109/ISCE.2008.4559553.

[:2-6] Garfinkel, Simson L. (2009). "Automating Disk Forensic Processing with SleuthKit, XML and Python". 2009 Fourth International IEEE Workshop on Systematic Approaches to Digital Forensic Engineering: 73–84. doi:10.1109/SADFE.2009.12.

[7] Kazim, Muhammad; Masood, Rahat; Shibli, Muhammad Awais (2013-11-26). "Securing the virtual machine images in cloud computing". Proceedings of the 6th International Conference on Security of Information and Networks. SIN '13. New York, NY, USA: Association for Computing Machinery: 425–428. doi:10.1145/2523514.2523576. ISBN 978-1-4503-2498-4.

[:7-8] Blackham, N., & Higby, C., & Bailey, M. (2004, June), Re Imaging Computers For Multipurpose Labs , 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--14125

[:4-9] Day, Michael; Pennock, Maureen; May, Peter; Davies, Kevin; Whibley, Simon; Kimura, Akiko; Halvarsson, Edith (2016). "The preservation of disk-based content at the British Library: Lessons from the Flashback project". Alexandria: The Journal of National and International Library and Information Issues. 26 (3): 216–234. doi:10.1177/0955749016669775. ISSN 0955-7490.

[10] Arunkumar, G.; Venkataraman., Neelanarayanan (2015-01-01). "A Novel Approach to Address Interoperability Concern in Cloud Computing". Procedia Computer Science. Big Data, Cloud and Computing Challenges. 50: 554–559. doi:10.1016/j.procs.2015.04.083. ISSN 1877-0509.

[11] Barrowclough, John Patrick; Asif, Rameez (2018-06-11). "Securing Cloud Hypervisors: A Survey of the Threats, Vulnerabilities, and Countermeasures". Security and Communication Networks. 2018: e1681908. doi:10.1155/2018/1681908. ISSN 1939-0114.{{cite journal}}: CS1 maint: unflagged free DOI (link)

[:10-12] Colloton, E., Farbowitz, J., Fortunato, F., & Gil, C. (2019). Towards Best Practices In Disk Imaging: A Cross-Institutional Approach. Electronic Media Review, 2019-2020.

[:5-13] Stewart, Dawid; Arvidsson, Alex (2022). Need for speed : A study of the speed of forensic disk imaging tools.

[14] "IBM Mainframe Operating Systems" (PDF). Archived from the original (PDF) on 2014-07-01. Retrieved 2014-06-17.

[15] McCune, Mike (2000). Integrating Linux and Windows. Prentice Hall Professional. ISBN 978-0-13-030670-8.

[16] Li, Hongwei; Yin, Changhong; Xu, Yaping; Guo, Qingjun (2010). "Construction of the Practical Teaching System on Operating Systems Course". 2010 Second International Workshop on Education Technology and Computer Science. 1: 405–408. doi:10.1109/ETCS.2010.184.

[17] "Phantom Burner Overview". Phantombility, Inc. Archived from the original on 19 August 2011. Retrieved 19 July 2011.

[18] "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.

[19] "Virtual CD/DVD-Writer Device". SourceForge. Geeknet, Inc. Archived from the original on 17 February 2011. Retrieved 19 July 2011.

[20] uide.com - Access Time

[21] Bowling, Jeramiah (2011-01-01). "Clonezilla: build, clone, repeat". Linux Journal. 2011 (201): 6:6. ISSN 1075-3583.

[:9-22] Shiau, Steven J. H.; Huang, Yu-Chiang; Tsai, Yu-Chin; Sun, Chen-Kai; Yen, Ching-Hsuan; Huang, Chi-Yo (2021). "A BitTorrent Mechanism-Based Solution for Massive System Deployment". IEEE Access. 9: 21043–21058. doi:10.1109/ACCESS.2021.3052525. ISSN 2169-3536.

[:8-23] Shiau, Steven J. H.; Sun, Chen-Kai; Tsai, Yu-Chin; Juang, Jer-Nan; Huang, Chi-Yo (2018). "The Design and Implementation of a Novel Open Source Massive Deployment System". Applied Sciences. 8 (6): 965. doi:10.3390/app8060965. ISSN 2076-3417.{{cite journal}}: CS1 maint: unflagged free DOI (link)

[24] "Fast, Scalable Disk Imaging with Frisbee". www.cs.utah.edu. Retrieved 2023-01-12.

[:6-25] Durno, John; Trofimchuk, Jerry (2015-01-21). "Digital forensics on a shoestring: a case study from the University of Victoria". The Code4Lib Journal (27). ISSN 1940-5758.

[26] "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.

[27] "Mount-DiskImage". Storage Cmdlets (TechNet). Microsoft. Archived from the original on 2017-12-01.

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 {{Redirect|CD image|ISO 9660 image files|ISO image}}
+A '''disk image''' is a snapshot of a storage device's structure and data typically stored in one or more computer files on another storage device.<ref name=":0">{{Cite journal |date=2022-11-02 |title=Disk Imaging as a Backup Tool for Digital Objects |url=https://www.taylorfrancis.com/chapters/edit/10.4324/9781003034865-17/disk-imaging-backup-tool-digital-objects-eddy-colloton-jonathan-farbowitz-caroline-gil-rodr%C3%ADguez |journal=Conservation of Time-Based Media Art |language=en |pages=204–222 |doi=10.4324/9781003034865-17}}</ref><ref name=":3" /> Traditionally, disk images were bit-by-bit copies of every sector on a hard disk often created for digital forensic purposes, but it is now common to only copy allocated data to reduce storage space.<ref name=":1">Pullakandam, R., Lin, X., Hibler, M., Eide, E., & Ricci, R. High-performance Disk Imaging With Deduplicated Storage.</ref><ref>{{Citation |last=Kävrestad |first=Joakim |title=Vocabulary |date=2017 |url=https://doi.org/10.1007/978-3-319-67450-6_12 |work=Guide to Digital Forensics: A Concise and Practical Introduction |pages=125–126 |editor-last=Kävrestad |editor-first=Joakim |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-67450-6_12 |isbn=978-3-319-67450-6 |access-date=2023-01-12}}</ref> [[Data compression|Compression]] and [[deduplication]] are commonly used to reduce the size of the image file set.<ref name=":1" /><ref>{{Cite journal |last=Lee |first=Sang Su |last2=Kyong |first2=Un Sung |last3=Hong |first3=Do Won |date=2008 |title=A high speed disk imaging system |url=https://ieeexplore.ieee.org/abstract/document/4559553 |journal=2008 IEEE International Symposium on Consumer Electronics |pages=1–3 |doi=10.1109/ISCE.2008.4559553}}</ref> Disk imaging is done for a variety of purposes including digital forensics<ref name=":2">{{Cite journal |last=Garfinkel |first=Simson L. |date=2009 |title=Automating Disk Forensic Processing with SleuthKit, XML and Python |url=https://ieeexplore.ieee.org/abstract/document/5341559 |journal=2009 Fourth International IEEE Workshop on Systematic Approaches to Digital Forensic Engineering |pages=73–84 |doi=10.1109/SADFE.2009.12}}</ref><ref name=":3">{{Cite journal |last=Woods |first=Kam |last2=Lee |first2=Christopher A. |last3=Garfinkel |first3=Simson |date=2011-06-13 |title=Extending digital repository architectures to support disk image preservation and access |url=https://doi.org/10.1145/1998076.1998088 |journal=Proceedings of the 11th annual international ACM/IEEE joint conference on Digital libraries |series=JCDL '11 |location=New York, NY, USA |publisher=Association for Computing Machinery |pages=57–66 |doi=10.1145/1998076.1998088 |isbn=978-1-4503-0744-4}}</ref>, [[cloud computing]]<ref>{{Cite journal |last=Kazim |first=Muhammad |last2=Masood |first2=Rahat |last3=Shibli |first3=Muhammad Awais |date=2013-11-26 |title=Securing the virtual machine images in cloud computing |url=https://doi.org/10.1145/2523514.2523576 |journal=Proceedings of the 6th International Conference on Security of Information and Networks |series=SIN '13 |location=New York, NY, USA |publisher=Association for Computing Machinery |pages=425–428 |doi=10.1145/2523514.2523576 |isbn=978-1-4503-2498-4}}</ref>, [[System administrator|system administration]]<ref name=":7">Blackham, N., & Higby, C., & Bailey, M. (2004, June), ''[https://peer.asee.org/re-imaging-computers-for-multipurpose-labs# Re Imaging Computers For Multipurpose Labs]'' , 2004 Annual Conference, Salt Lake City, Utah. 10.18260/1-2--14125</ref>, as part of a backup strategy,<ref name=":0" /> and legacy emulation as part of a [[digital preservation]] strategy.<ref name=":4">{{Cite journal |last=Day |first=Michael |last2=Pennock |first2=Maureen |last3=May |first3=Peter |last4=Davies |first4=Kevin |last5=Whibley |first5=Simon |last6=Kimura |first6=Akiko |last7=Halvarsson |first7=Edith |date=2016 |title=The preservation of disk-based content at the British Library: Lessons from the Flashback project |url=http://journals.sagepub.com/doi/10.1177/0955749016669775 |journal=Alexandria: The Journal of National and International Library and Information Issues |language=en |volume=26 |issue=3 |pages=216–234 |doi=10.1177/0955749016669775 |issn=0955-7490}}</ref> Disk images can be made in a variety of formats depending on the purpose. Virtual disk images (such as VHD and VMDK) are intended to be used for cloud computing<ref>{{Cite journal |last=Arunkumar |first=G. |last2=Venkataraman. |first2=Neelanarayanan |date=2015-01-01 |title=A Novel Approach to Address Interoperability Concern in Cloud Computing |url=https://www.sciencedirect.com/science/article/pii/S1877050915005840 |journal=Procedia Computer Science |series=Big Data, Cloud and Computing Challenges |language=en |volume=50 |pages=554–559 |doi=10.1016/j.procs.2015.04.083 |issn=1877-0509}}</ref><ref>{{Cite journal |last=Barrowclough |first=John Patrick |last2=Asif |first2=Rameez |date=2018-06-11 |title=Securing Cloud Hypervisors: A Survey of the Threats, Vulnerabilities, and Countermeasures |url=https://www.hindawi.com/journals/scn/2018/1681908/ |journal=Security and Communication Networks |language=en |volume=2018 |pages=e1681908 |doi=10.1155/2018/1681908 |issn=1939-0114}}</ref>, [[ISO Image|ISO images]] are intended to emulate optical media<ref name=":10">Colloton, E., Farbowitz, J., Fortunato, F., & Gil, C. (2019). [https://resources.culturalheritage.org/emg-review/volume-6-2019-2020/colloton/ Towards Best Practices In Disk Imaging: A Cross-Institutional Approach]. ''Electronic Media Review'', 2019-2020.</ref> and [[Raw image format|RAW disk images]] are used for forensic purposes.<ref name=":3" /> Proprietary formats are typically used by disk imaging software. Despite the benefits of disk imaging the storage costs can be high<ref name=":1" />, management can be difficult<ref name=":2" /> and they can be time consuming to create.<ref name=":5">{{Cite book |last=Stewart |first=Dawid |url=http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-47045 |title=Need for speed : A study of the speed of forensic disk imaging tools |last2=Arvidsson |first2=Alex |date=2022}}</ref><ref name=":4" />
-A '''disk image''', in computing, is a [[computer file]] containing the contents and structure of a disk [[volume (computing)|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 [[disk sector|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.
+==Background==
-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.
+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 [[megabyte]]s and as large as 330 megabytes, and the copy medium was [[magnetic tape]], which ran as large as 200 megabytes per reel.<ref>{{cite web|title=IBM Mainframe Operating Systems|url=http://www.demorton.com/Tech/$OSTL.pdf|access-date=2014-06-17|url-status=dead|archive-url=https://web.archive.org/web/20140701185435/http://www.demorton.com/Tech/$OSTL.pdf|archive-date=2014-07-01}}</ref> 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.
-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 [[data compression|compress]] the used space.
+Disk image creation is called disk imaging and is often time consuming, even with a fast computer, because the entire disk must be copied.<ref name=":5" /> Typically, disk imaging requires a third party disk imaging program or backup software. The software required varies according to the type of disk image that needs to be created. For example, RawWrite and WinImage create [[IMG (file format)|floppy disk image]] files for [[MS-DOS]] and [[Microsoft Windows]].<ref>{{Cite book |last=McCune |first=Mike |url=https://books.google.com.au/books?hl=en&lr=&id=0SM3PEH9gagC&oi=fnd&pg=PR1&dq=%22RawWrite%22+++%22floppy%22&ots=g2bK1tbMb4&sig=bc04FUlRMPQizPwP3r5MLkR-ewo&redir_esc=y#v=onepage&q=rawwrite&f=false |title=Integrating Linux and Windows |date=2000 |publisher=Prentice Hall Professional |isbn=978-0-13-030670-8 |language=en}}</ref><ref>{{Cite journal |last=Li |first=Hongwei |last2=Yin |first2=Changhong |last3=Xu |first3=Yaping |last4=Guo |first4=Qingjun |date=2010 |title=Construction of the Practical Teaching System on Operating Systems Course |url=https://ieeexplore.ieee.org/abstract/document/5458788 |journal=2010 Second International Workshop on Education Technology and Computer Science |volume=1 |pages=405–408 |doi=10.1109/ETCS.2010.184}}</ref> In [[Unix]] or [[Unix-like|similar systems]] the [[dd (Unix)|dd]] program can be used to create raw disk images.<ref name=":3" /> [[Apple Disk Copy]] can be used on [[Classic Mac OS]] and [[macOS]] systems to create and write disk image files.
-==History==
+Authoring software for CDs/DVDs such as [[Nero Burning ROM]] can generate and load disk images for optical media. 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.<ref>{{cite web |title=Phantom Burner Overview |url=http://www.phantombility.com/en/prod/phantomburner/ |url-status=dead |archive-url=https://web.archive.org/web/20110819141722/http://phantombility.com/en/prod/phantomburner |archive-date=19 August 2011 |access-date=19 July 2011 |publisher=Phantombility, Inc}}</ref><ref>{{cite web |title=Virtual CD - The original for your PC |url=http://www.virtualcd.de/vcd/apps/overview/original.cfm?lg=0 |url-status=live |archive-url=https://web.archive.org/web/20110924022331/http://www.virtualcd.de/vcd/apps/overview/original.cfm?lg=0 |archive-date=24 September 2011 |access-date=19 July 2011 |work=Virtual CD website |publisher=H+H Software GmbH}}</ref> 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.<ref>{{cite web |title=Virtual CD/DVD-Writer Device |url=http://sourceforge.net/projects/virtualmedia/ |url-status=live |archive-url=https://web.archive.org/web/20110217075400/http://sourceforge.net/projects/virtualmedia/ |archive-date=17 February 2011 |access-date=19 July 2011 |work=[[SourceForge]] |publisher=Geeknet, Inc.}}</ref>
-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 [[megabyte]]s and as large as 330 megabytes, and the copy medium was [[magnetic tape]], which ran as large as 200 megabytes per reel.<ref>{{cite web|title=IBM Mainframe Operating Systems|url=http://www.demorton.com/Tech/$OSTL.pdf|access-date=2014-06-17|url-status=dead|archive-url=https://web.archive.org/web/20140701185435/http://www.demorton.com/Tech/$OSTL.pdf|archive-date=2014-07-01}}</ref> 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==
+===Digital forensics===
-Disk images are used for duplication of optical media including DVDs, Blu-ray discs, etc. It is also used to make perfect [[Disk cloning|clones of hard disks]].
+Forensic imaging is the process of creating a bit-by-bit copy of the data on the drive, including files, metadata, volume information, filesystems and their structure.<ref name=":3" /> Often, these images are also hashed to verify their integrity and that they have not been altered since being created. Unlike disk imaging for other purposes, digital forensic applications take a bit-by-bit copy to ensure forensic soundness. The purposes of imaging the disk is to not only discover evidence preserved in digital information but also to examine the drive to gather clues of how the crime was committed.
+===Cloud computing===
-A [[virtual disk]] may emulate any type of physical drive, such as a hard disk drive, [[tape drive]], [[USB flash drive|key drive]], [[floppy drive]], [[compact disc|CD]]/[[DVD]]/[[Blu-ray Disc|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 [[random-access memory|RAM]] for fast read/write access (known as a [[RAM disk]]), or on a hard drive. Typical uses of virtual drives include the [[Mount_(computing)|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").
+In cloud computing, creating a disk image of optical media or a [[hard disk drive]] is especially useful. [[Virtual machine|Virtual machines]] emulate a CD/DVD drive by reading an [[ISO Image|ISO image]]. This can also be faster than reading from the physical optical medium.<ref>[https://web.archive.org/web/20190110014217/http://www.pcguide.com/ref/cd/perfAccess-c.html pcguide.com - Access Time]</ref> Further, there are less issues with wear and tear. A [[hard disk drive]] or [[solid-state drive]] in a [[virtual machine]] is implemented as a disk image, stored either as a collection of files, collectively called a ''split'' flat file, where each one is typically 2GB in size, or as a single, large ''monolithic'' flat file. Virtual machines treat the image as a physical disk.
+=== System administration ===
-Some [[Operating_system | operating systems]] such as [[Linux]]<ref name="linuxhelp">{{cite web |url= http://www.linuxhelp.net/linux_downloads/ |title= Linux ISO Images |publisher= LinuxHelp.net |access-date= 2007-03-23 |url-status= live |archive-url= https://web.archive.org/web/20070302124256/http://www.linuxhelp.net/linux_downloads/ |archive-date= 2007-03-02 }}</ref> and [[macOS]]<ref name="osx-dim">Although macOS's built-in DiskImageMounter software does not emulate a physical drive</ref> 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.<ref>{{cite web |url= http://blogs.msdn.com/b/b8/archive/2011/08/30/accessing-data-in-iso-and-vhd-files.aspx |title= Accessing data in ISO and VHD files |work= Building Windows 8 (TechNet Blogs) |publisher= Microsoft |date= 30 August 2011 |access-date= 27 April 2012 |url-status= live |archive-url= https://web.archive.org/web/20120419080359/http://blogs.msdn.com/b/b8/archive/2011/08/30/accessing-data-in-iso-and-vhd-files.aspx |archive-date= 19 April 2012 }}</ref><ref>{{cite web |url= https://technet.microsoft.com/en-us/library/hh848706(v=wps.620).aspx |title= Mount-DiskImage |work= Storage Cmdlets (TechNet) |publisher= Microsoft |url-status= live |archive-url= https://web.archive.org/web/20171201030435/https://technet.microsoft.com/en-us/library/hh848706(v=wps.620).aspx |archive-date= 2017-12-01 }}</ref>
+==== Rapid deployment of clone systems ====
-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 [[Optical_disc_drive | CD/DVD drives]] which can produce new disk images; this type of virtual drive goes by a variety of names, including "virtual burner".
+Educational institutions and businesses can often need to buy or replace computer systems in large numbers. Disk imaging is commonly used to deploy the same configuration across workstations.<ref name=":7" /> Typically, disk imaging software (such as [[Ghost (disk utility)|Ghost]] or [[Clonezilla]]) is used to make an image of a completely configured system.<ref>{{Cite journal |last=Bowling |first=Jeramiah |date=2011-01-01 |title=Clonezilla: build, clone, repeat |url=https://dl.acm.org/doi/10.5555/1924401.1924407 |journal=Linux Journal |volume=2011 |issue=201 |pages=6:6 |issn=1075-3583}}</ref> This image is then written to a computer's hard disk which is sometimes described as restoring an image.<ref name=":9">{{Cite journal |last=Shiau |first=Steven J. H. |last2=Huang |first2=Yu-Chiang |last3=Tsai |first3=Yu-Chin |last4=Sun |first4=Chen-Kai |last5=Yen |first5=Ching-Hsuan |last6=Huang |first6=Chi-Yo |date=2021 |title=A BitTorrent Mechanism-Based Solution for Massive System Deployment |url=https://ieeexplore.ieee.org/abstract/document/9328243 |journal=IEEE Access |volume=9 |pages=21043–21058 |doi=10.1109/ACCESS.2021.3052525 |issn=2169-3536}}</ref> This restoration is sometimes done over a computer network using [[multicasting]] or [[BitTorrent]] to devices that need to have their configuration restored.<ref name=":8">{{Cite journal |last=Shiau |first=Steven J. H. |last2=Sun |first2=Chen-Kai |last3=Tsai |first3=Yu-Chin |last4=Juang |first4=Jer-Nan |last5=Huang |first5=Chi-Yo |date=2018 |title=The Design and Implementation of a Novel Open Source Massive Deployment System |url=https://www.mdpi.com/2076-3417/8/6/965 |journal=Applied Sciences |language=en |volume=8 |issue=6 |pages=965 |doi=10.3390/app8060965 |issn=2076-3417}}</ref><ref name=":9" /> This reduces the need to maintain and update individual systems manually. Imaging is also easier than automated setup methods for deploying a computer because an administrator does need to have knowledge of the prior configuration to copy it.<ref name=":9" /> Disk imaging requires for all devices to be identical and provides no flexibility in adjusting the configuration.
+Network-based image deployment typically uses a [[Preboot Execution Environment|PXE]] server to boot a minimal operating system over the network that contains the necessary components to image or restore storage media in a computer.<ref name=":8" /> This is usually used in conjunction with a DHCP server to automate the configuration of network parameters including [[IP address|IP addresses]]. Typically, [[Multicast|multicasting]], [[Broadcasting (networking)|broadcasting]] or [[Unicast|unicasting]] is used to restore an image to many computers at a time but these approaches do not work well if one or more computers experience a problem such as [[User Datagram Protocol|UDP]] packet loss.<ref name=":9" /> As a result, some imaging solutions instead use the [[BitTorrent|BitTorret]] protocol to transfer the data.
-===Enhancement===
-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,<ref>[https://web.archive.org/web/20190110014217/http://www.pcguide.com/ref/cd/perfAccess-c.html pcguide.com - Access Time]</ref> are quieter, suffer from less wear and tear, and in the case of [[solid-state drive]]s, 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).
+===Backup strategy===
-Virtual drives may also be used as part of emulation of an entire machine (a [[virtual machine]]).
-===Software distribution===
-Since the spread of broadband, CD and DVD images have become a common medium for [[Linux distribution]]s.<ref name="linuxhelp"/> 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 little
-or 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.<ref>{{cite web |title=Software Distribution |url=http://software.dell.com/products/kace-k1000-systems-management-appliance/software-distribution.aspx |publisher=Dell KACE |access-date=2015-10-01 |url-status=dead |archive-url=https://web.archive.org/web/20151003031633/http://software.dell.com/products/kace-k1000-systems-management-appliance/software-distribution.aspx |archive-date=2015-10-03 }}</ref> 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 [[software]] [[downloads]], 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 [[Microsoft Windows|Windows]] are also sometimes distributed as disk images including [[ISO image]]s. 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===
-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===
-A [[hard disk drive]] or [[solid-state drive]] in a [[virtual machine]] is implemented as a disk image, stored either as a collection of flat files, collectively called a ''split'' flat file, where each one is typically 2GB in size, or as a single, large ''monolithic'' flat file.
-Disk image formats include the [[VHD (file format)|VHD]] format used by Microsoft's [[Hyper-V]], the [[VDI (file format)|VDI]] format used by [[Oracle Corporation]]'s [[VirtualBox]], the [[VMDK]] format used for [[VMware]] virtual machines, and the [[QCOW]] format used by [[QEMU]].
-===Forensic imaging===
-Forensic imaging is the process that involves copying the contents and recording an image of the entire drives contents (imaging) into a single file (or a very small number of files). A component of forensic imaging involves verification of the values imaged to ensure the integrity of the file(s) imaged. Forensic images are created using software tools that can be acquired. 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.
-Forensic images are typically acquired using software tools compatible with their system. Note that some forensic imaging software tools may have limitations in terms of the software's ability to communicate, diagnose, or repair storage mediums that (often times) are experiencing errors or even a failure of some internal component.
-===Data recovery===
-[[Data recovery]] imaging is the process of imaging each sector, systematically, on the source drive to another destination storage medium from which required files can then be retrieved. In data recovery situations, one cannot always rely on the integrity of their particular file structure and therefore a complete sector copy is mandatory to imaging end there though.
-===System backup===
 {{See also2|[[System image]]|[[Backup and Restore]] (for Windows Vista and later)}}
-Some backup programs only [[data backup|back up]] user files; [[booting|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, including [[file attribute]]s and the [[file fragmentation]] state. For this reason, it is also used for backing up [[optical media]] ([[CD]]s and [[DVD]]s, etc.), and allows the exact and efficient recovery after [[Sandbox_(software_development)|experimenting]] with modifications to a system or [[virtual machine]], in one go.
+A disk image contains all files, faithfully replicating all data, including [[file attribute]]s and the [[file fragmentation]] state. For this reason, it is also used for backing up [[optical media]] ([[CD]]s and [[DVD]]s, etc.), and allows the exact and efficient recovery after [[Sandbox_(software_development)|experimenting]] with modifications to a system or [[virtual machine]]. Typically, disk imaging can be used to quickly restore an entire system to an operational state after a disaster.<ref>{{Cite web |title=Fast, Scalable Disk Imaging with Frisbee |url=https://www.cs.utah.edu/flux/papers/frisbee-usenix03/frisbee-www.html |access-date=2023-01-12 |website=www.cs.utah.edu}}</ref>
-There are benefits and drawbacks to both "file-based" and "bit-identical" image backup methods. 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 filename]]s, 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 (unix)|dd]], available on nearly all [[live CD]]s.
-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. 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===
-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 [[Standard operating environment|fully prepared software environment]] of a reference system. This method saves time and effort and allows administrators to focus on each systems unique [[idiosyncrasies]] they 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 transfer
-information-rich disk images at lightning speeds, which is a significant improvement over the days when programmers spent hours configuring each machine within an organization.<ref>{{cite web |title=Disk Imaging |url=http://software.dell.com/products/kace-k2000-systems-deployment-appliance/disk-imaging.aspx |publisher=Dell KACE |access-date=2015-10-01 |url-status=live |archive-url=https://web.archive.org/web/20151002205915/http://software.dell.com/products/kace-k2000-systems-deployment-appliance/disk-imaging.aspx |archive-date=2015-10-02 }}</ref>
-===Legacy hardware emulation===
-[[Emulator]]s frequently use disk images to simulate the floppy drive of the computer being emulated. 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===
-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 [[kilobyte]]s, 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==
-Creating a disk image is achieved with a suitable program. Different [[Comparison_of_disk_cloning_software | disk imaging programs]] have varying capabilities, and may focus on hard drive imaging (including [[hard drive]] [[backup]], 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.<ref>{{cite web|title=Phantom Burner Overview|url=http://www.phantombility.com/en/prod/phantomburner/|publisher=Phantombility, Inc|access-date=19 July 2011|url-status=dead|archive-url=https://web.archive.org/web/20110819141722/http://phantombility.com/en/prod/phantomburner|archive-date=19 August 2011}}</ref><ref>{{cite web|title=Virtual CD - The original for your PC|url=http://www.virtualcd.de/vcd/apps/overview/original.cfm?lg=0|work=Virtual CD website|publisher=H+H Software GmbH|access-date=19 July 2011|url-status=live|archive-url=https://web.archive.org/web/20110924022331/http://www.virtualcd.de/vcd/apps/overview/original.cfm?lg=0|archive-date=24 September 2011}}</ref> 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.<ref>{{cite web|title=Virtual CD/DVD-Writer Device|url=http://sourceforge.net/projects/virtualmedia/|work=[[SourceForge]]|publisher=Geeknet, Inc.|access-date=19 July 2011|url-status=live|archive-url=https://web.archive.org/web/20110217075400/http://sourceforge.net/projects/virtualmedia/|archive-date=17 February 2011}}</ref>
-==File formats==
-* [[IMG (file format)]]
-==Utilities==
-RawWrite and WinImage are examples of [[IMG (file format)|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.
+===Digital preservation===
-In [[Unix]] or [[Unix-like|similar systems]] the [[dd (Unix)|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]].
+Libraries and museums are typically required to archive and digitally preserve information without altering it in any matter.<ref name=":4" /><ref name=":6">{{Cite journal |last=Durno |first=John |last2=Trofimchuk |first2=Jerry |date=2015-01-21 |title=Digital forensics on a shoestring:  a case study from the University of Victoria |url=https://journal.code4lib.org/articles/10279?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+c4lj+ |journal=The Code4Lib Journal |issue=27 |issn=1940-5758}}</ref> [[Emulator]]s frequently use disk images to emulate floppy disks that have been preserved. 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. Emulation also allows existing disk images to be put into a usable form even though the data contained in the image is no longer readable without emulation.<ref name=":10" />
+== Limitations ==
-[[Apple Disk Copy]] can be used on [[Classic Mac OS]] and [[macOS]] systems to create and write disk image files.
+Disk images can sometimes be slower than reading from the disk directly because of a performance overhead.<ref name=":1" /> Other limitations can be the lack of access to software required to read the contents of the image. For example, prior to Windows 8, third party software was required to mount disk images.<ref>{{cite web |date=30 August 2011 |title=Accessing data in ISO and VHD files |url=http://blogs.msdn.com/b/b8/archive/2011/08/30/accessing-data-in-iso-and-vhd-files.aspx |url-status=live |archive-url=https://web.archive.org/web/20120419080359/http://blogs.msdn.com/b/b8/archive/2011/08/30/accessing-data-in-iso-and-vhd-files.aspx |archive-date=19 April 2012 |access-date=27 April 2012 |work=Building Windows 8 (TechNet Blogs) |publisher=Microsoft}}</ref><ref>{{cite web |title=Mount-DiskImage |url=https://technet.microsoft.com/en-us/library/hh848706(v=wps.620).aspx |url-status=live |archive-url=https://web.archive.org/web/20171201030435/https://technet.microsoft.com/en-us/library/hh848706(v=wps.620).aspx |archive-date=2017-12-01 |work=Storage Cmdlets (TechNet) |publisher=Microsoft}}</ref> Disk imaging is time consuming and the space requirements are high. When imaging multiple computers with only minor differences, much data is duplicated unnecessarily, wasting space.<ref name=":1" />
+=== Speed and failure ===
-Authoring software for CDs/DVDs such as [[Nero Burning ROM]] can generate and load disk images for optical media.
+Disk imaging can be slow, especially for older storage devices. A typical 4.7 GB DVD can take an average of 18 minutes to duplicate.<ref name=":4" /> Floppy disks read and write much slower than hard disks. Therefore, despite their small size, it can take several minutes to copy a single disk. In some cases, disk imaging can fail due to bad sectors or physical wear and tear on the source device.<ref name=":10" /> Utilities such as [[Dd (Unix)|dd]] are not designed to recognize or cope with failures. Therefore, any failure results in being unable to create an image of the drive.<ref name=":6" />
 ==See also==

v t e Virtual drive software
Virtual disk image RAM disk Mount
Free software	AcetoneISO CDemu K3b mount WinCDEmu
Proprietary software	Alcohol 120% Daemon Tools DiskImageMounter Disk Utility MagicISO Roxio Toast UltraISO Virtual CloneDrive VirtualDrive Pro
Comparison of disc image software

v t e Disk image file formats
Comparison of disc image software
Optical discs	BIN+CUE DAA IMG+CCD+SUB ISO ISZ MDF+MDS MDX NRG UIF
Hard disks	DMG FVD IMG ISO NDIF QCOW UDIF VDI VHD VMDK WIM
Floppy disks	ADF, ADZ DC42, DART DMS IMG, IMA, IMZ VFD
CD-DA	Disc Description Protocol
Convention: Any item in this table that has the form of "A+B" or "A+B+C" indicates a disk format that spans multiple files, where A contains the bulk of the data, and B and C are sidecar files.

v t e Pirated movie release types
Pre-release	R5 Screener (SCR) Telecine (TC) Workprint (WP)
In-cinema	Cam Telesync (TS)
Home video ripping	Disk image PDTV