What Is Mac Open Base Dmg
DMG files are specific to Mac OS X, though can be opened in Windows using an application such as TransMac. Additionally, tools such as IsoBuster and DMG2ISO can be used to convert DMG files to more recognizable formats such as File extension ISO or File extension BIN, which can be opened using a wide range of applications or burnt straight to disc using software such as Roxio or Nero. DMG is used for disk image files on Macintosh computers running Mac OS X. This file extension replaces the older file extension IMG which was discontinued during the release of later series of Mac operating systems. You can open DMG file on Mac, Linux, and Windows operating systems but it will require additional software to be installed on Windows. Since DMG is a native Mac OS disk image format opening DMG file is as easy as double clicking on it in Finder. Downloaded dmg file burn a dvd for os install. When you open DMG file this way, disk image stored inside DMG file will be mounted, and then opened in a separate Finder window. If DMG contains installation of an application, then installation window of the app will open. Nov 12, 2019 When a Mac user downloads a DMG file, he can simply double-click it to open it with the DiskImageMounter utility that comes with macOS. When the DMG file is opened, it mounts a virtual disk on the desktop and in an Apple Finder window as if it was a CD or a USB flash drive that was just inserted into the computer. Nov 13, 2019 Review the DMG's contents. Most of the time, you'll use DMG files to install an app. However, some DMG files contain images or text files as well. Anything ending in.app is an installable app. You'll most likely see an 'Applications' icon in the DMG window. This is a shortcut to your Mac's Applications folder.
The icon represents an internal hard drive within a generic file icon. | |
Filename extension | .dmg, .smi, .img |
---|---|
Internet media type | application/x-apple-diskimage |
Uniform Type Identifier (UTI) | com.apple.disk-image |
Developed by | Apple Inc. |
Type of format | Disk image |
Apple Disk Image is a disk image format commonly used by the macOS operating system. When opened, an Apple Disk Image is mounted as a volume within the Macintosh Finder.
An Apple Disk Image can be structured according to one of several proprietary disk image formats, including the Universal Disk Image Format (UDIF) and the New Disk Image Format (NDIF). An Apple disk image file's name usually has '.dmg' as its extension.
Features[edit]
What Is Dmg File
Apple Disk Image files are published with a MIME type of application/x-apple-diskimage.
Different file systems can be contained inside these disk images, and there is also support for creating hybrid optical media images that contain multiple file systems.[1] Some of the file systems supported include Hierarchical File System (HFS), HFS Plus, File Allocation Table (FAT), ISO9660 and Universal Disk Format (UDF).[1][2]
Apple Disk Images can be created using utilities bundled with Mac OS X, specifically Disk Copy in Mac OS X v10.2 and earlier and Disk Utility in Mac OS X v10.3 and later. These utilities can also use Apple disk image files as images for burning CDs and DVDs. Disk image files may also be managed via the command line interface using the hdiutil utility.[3]
What Is Dmg Used For
In Mac OS X v10.2.3, Apple introduced Compressed Disk Images[4] and Internet-Enabled Disk Images for use with the Apple utility Disk Copy, which was later integrated into Disk Utility in 10.3. The Disk Copy application had the ability to display a multi-lingual software license agreement before mounting a disk image. Mac os 10.5 dmg download. The image will not be mounted unless the user indicates agreement with the license.[5]
An Apple Disk Image allows secure password protection as well as file compression, and hence serves both security and file distribution functions; such a disk image is most commonly used to distribute software over the Internet.
History[edit]
Apple originally created its disk image formats because the resource fork used by Mac applications could not easily be transferred over mixed networks such as those that make up the Internet. Even as the use of resource forks declined with Mac OS X, disk images remained the standard software distribution format. Disk images allow the distributor to control the Finder's presentation of the window, which is commonly used to instruct the user to copy the application to the correct folder.
A previous version of the format, intended only for floppy disk images, is usually referred to as 'Disk Copy 4.2' format, after the version of the Disk Copy utility that was used to handle these images.[1] A similar format that supported compression of floppy disk images is called DART.[1][6]
New Disk Image Format (NDIF) was the previous default disk image format in Mac OS 9,[1] and disk images with this format generally have a .img (not to be confused with raw .img disk image files) or .smi file extension. Files with the .smi extension are actually applications that mount an embedded disk image, thus a 'Self Mounting Image', and are intended only for Mac OS 9 and earlier.[7][2]
Universal Disk Image Format (UDIF) is the native disk image format for Mac OS X. Disk images in this format typically have a .dmg extension.[1]
File format[edit]
Apple has not released any documentation on the format, but attempts to reverse engineer parts of the format have been successful. The encrypted layer was reverse engineered in an implementation called VileFault[8] (a spoonerism of FileVault).
Apple disk image files are essentially raw disk images (i.e. contain block data) with some added metadata, optionally with one or two layers applied that provide compression and encryption. In hdiutil these layers are called CUDIFEncoding and CEncryptedEncoding.[1]
UDIF supports ADC (an old proprietary compression format by Apple), zlib, bzip2 (as of Mac OS X v10.4), and LZFSE (as of Mac OS X v10.11)[9] compression internally.
Trailer[edit]
The trailer can be described using the following C structure.[10] All values are big-endian (PowerPC byte ordering)
Here is an explanation:
Position(in Hex) | Length (in bytes) | Description |
---|---|---|
000 | 4 | Magic bytes ('koly'). |
004 | 4 | File version (current is 4) |
008 | 4 | The length of this header, in bytes. Should be 512. |
00C | 4 | Flags. |
010 | 8 | Unknown. |
018 | 8 | Data fork offset (usually 0, beginning of file) |
020 | 8 | Size of data fork (usually up to the XMLOffset, below) |
028 | 8 | Resource fork offset, if any |
030 | 8 | Resource fork length, if any |
038 | 4 | Segment number. Usually 1, may be 0 |
03C | 4 | Segment count. Usually 1, may be 0 |
040 | 16 | 128-bit GUID identifier of segment |
050 | 4 | Data fork checksum type |
054 | 4 | Data fork checksum size |
058 | 128 | Data fork checksum |
0D8 | 8 | Offset of XML property list in DMG, from beginning |
0E0 | 8 | Length of XML property list |
0E8 | 120 | Reserved bytes |
160 | 4 | Master checksum type |
164 | 4 | Master checksum size |
168 | 128 | Master checksum |
1E8 | 4 | Unknown, commonly 1 |
1EC | 8 | Size of DMG when expanded, in sectors |
1F4 | 12 | Reserved bytes (zeroes) |
Utilities[edit]
There are few options available to extract files or mount the proprietary Apple Disk Image format. Some cross-platform conversion utilities are:
- dmg2img was originally written in Perl; however, the Perl version is no longer maintained, and the project was rewritten in C. Currently, without additional tools, the resulting images may be mounted only under Mac OS X and under Linux (provided hfsplus support has been enabled). UDIF ADC-compressed images have been supported since version 1.5.[11]
- DMGEXtractor is written in Java with GUI, and it supports more advanced features of dmg including AES-128 encrypted images but not UDCO images.[12]
- 7-Zip, including the free cross-platform port of its command-line interface, p7zip.
In Windows, most dmg images can be opened using several other programs such as UltraISO and IsoBuster. MacDrive can also mount simple dmg files as drives under windows, but not sparse disk or encrypted dmgs.[13] A free Apple DMG Disk Image Viewer also exists.[14]
In Linux and possibly other Unix flavors, most .dmg files can be burned to CD/DVD using any CD-burner program (using cdrecord directly or a front-end such as K3B or Brasero) or directly mounted to a mountpoint (e.g. mount -o loop,ro -t hfsplus imagefile.dmg /mnt/mountpoint
).[15][16] darling-dmg is a FUSE module enabling easy DMG file mounting on Linux.[17]
See also[edit]
References[edit]
- ^ abcdefg'hdiutil(1) Mac OS X Manual Page'. Archived from the original on 2016-05-14. Retrieved 2016-05-14.
- ^ ab'Mac OS X: Using Disk Copy disk image files'. Archived from the original on 2013-12-19. Retrieved 2013-04-25.
- ^
hdiutil(1)
– Darwin and macOS General Commands Manual - ^'Re: Some apps refuse to launch in 10.2.8! (OT, but very important)'. Archived from the original on 2014-01-17.
- ^'Guides'. Apple. Archived from the original on 2009-03-06. Retrieved 2010-10-27.
- ^'DART 1.5.3: Version Change History'. Archived from the original on 2013-12-19. Retrieved 2013-04-25.
- ^'Software Downloads: Formats and Common Error Messages'. Archived from the original on 2010-12-24. Retrieved 2009-05-06.
- ^'VileFault'. 2006-12-29. Archived from the original on 2007-01-09. Retrieved 2010-10-27.
- ^Michael Tsai (2015-10-07). 'LZFSE Disk Images in El Capitan'. Archived from the original on 2017-04-09. Retrieved 2017-04-09.
- ^'Demystifying the DMG File Format'. Archived from the original on 2013-03-17.
- ^'dmg2img'. Archived from the original on 29 November 2010. Retrieved 2010-10-27.
- ^'DMGExtractor'. Archived from the original on 2011-01-02. Retrieved 2011-01-03.
- ^MacDrive Features / Boot Camp / System Requirements /. 'MacDrive Home page'. Mediafour. Archived from the original on 4 October 2010. Retrieved 2010-10-27.
- ^Olivia Dehaviland (2015-03-03). 'Apple DMG Disk Image Viewer'. DataForensics.org. Archived from the original on 2015-04-02. Retrieved 2015-03-10.
- ^'How To Convert DMG To ISO in Windows, Linux & Mac'. Archived from the original on 2010-03-07.
- ^'Convert DMG To ISO using PowerISO'. Archived from the original on 2009-05-02. Retrieved 2009-02-15.
- ^'darling-dmg'. darling-dmg. Retrieved 29 March 2015.
External links[edit]
- Apple Developer Connection A Quick Look at PackageMaker and Installer
- O'Reilly Mac DevCenter Tip 16-5. Create a Disk Image from a Directory in the Terminal