Using the FAQ
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An image is a file containing the whole contents of a CD-ROM (or of another kind of disk or storage medium). Most burning softwares allow the user to store on the hard disk an image of the future CD-ROM. In most situations, this is to avoid the big problem called "buffer underrun" (when the data buffer becomes empty because the files are not copied to the buffer fast enough). In other cases, you keep the image to burn successively several copies, saving this way the preparation work.
On this page, we use both expressions ("image file" and "CD-ROM image") to refer to the same thing.
See below about ISO, HFS and hybrid images.
An ISO image is an image (see above) of an ISO 9660 CD-ROM. The ISO 9660 standard defines the file system used on most CD-ROMs (HFS CD-ROMs being one exception). Some software packages create plain ISO 9660 images, other interpret the ISO as they like.
Nero uses the NRG suffix to name its ISO images.
ISO images created by Easy CD Creator contain some lead-in and lead-out bytes around the core of the 2048-byte sector. This explains why ISO images created by Easy CD Creator can't be burnt by all burning packages (CDRWin complains about the file not beeing a multiple of the sector size, for an example). On the other hand, Easy CD Creator can burn plain ISO images (ISO images written by other packages).
A HFS image is an image (see above) containing a HFS (Macintosh) volume. HFS is the acronym for Hierarchical File System and designates the Macintosh file system. The HFS image can be the result of a raw copy from a physical disk with our Hybridator or a virtual Macintosh partition created by our MacImage. It contains the whole file system and can be burnt onto a CD-ROM with your favorite burning software to produce a Macintosh CD-ROM (a CD-ROM which will be readable on a Macintosh only).
|Different image formats and their extensions
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Almost all CD-ROM burning packages have their own CD-ROM image format, and a specific file extension (suffix) to identify them. Here are some ones we collected on the Internet:
|Program and comments|
|Easy CD Creator|
|Prassi (Global Image)|
|Easy CD Creator (see below some comments)|
|Nero (pure ISO 9660 images for data CD-ROMs)|
|Plextor Image file|
When asked to burn an image (menu 'File', item 'Create CD from Disk image', Easy CD Creator (ECDC) defaults to CIF files (a proprietary format based on the Riff standard). You have to select "*.iso" files (in some versions, you'll have so select "*.*") to select another kind of image file. The programs checks two points: the extension, which must be ISO, and the presence of the string "CD001" in the 16th sector. It will crash if one of those checks fails.
That means that you can't burn a non-standard CD-ROM image with ECDC, like the image of a pure HFS (Macintosh) disk image (Toast images, for example) or some other specific data layout on the disk.
There is no problem burning hybrid images compiled by MacImage. Note that even the pure HFS images created by MacImage contain this "CD001" string. Rename them with the ISO extension and ECDC should do its job.
Select the File menu, then the item Burn image. Ask for displaying all files (*.*) since Nero expects files with the NRG suffix, locate your image file and load it. Answer OK to the Foreign Image File prompt (if Nero doesn't recognize a true ISO image).
You then have to specify the parameters of the ISO file (this holds true for HFS images): Type of image: Data Mode 1. Block size: 2048. File precursor and image trailer: 0 length. No Scrambled and no Swapped.
If the program complains that there are errors in the image file, click on the button "Ignore" and launch the burning.
This information was found on the on-line help pages of Ahead/Nero site.
You need to create a Track Image project in WinOnCD for the image file. This item is in the Others menu. Please note that the program doesn't accept the iso suffix for the image, and that you'll have to rename it with the raw suffix.
Open the icon labeled "File Backup and Tools". In the listbox named "Backup/Tool Operation", select the item "Record an ISO 9660 Image File". In the box "ISO 9660 Image File", click on the button labeled "..." (aka of Browse) and select the ISO image file. At the bottom of the dialog box, leave the default options (CD-ROM and Mode 1). Check 'Open new session' if you want to be able to add another session later on. Then click on the button labelled "START".
A hybrid CD-ROM is a CD-ROM which can be loaded on a PC and on a Macintosh, where each user only sees the files s/he has to see. Hybrid CD-ROMs can share their data files (the same data file is visible from the ISO view and from the HFS view, but is only copied once to the medium) or not (both partitions are totally independant). Our program MacImage can produce both kinds of CD-ROMs on the PC.
See also our page on Macintosh CD-ROMs for more information.
An ISO 9660 CD-ROM, even if it sometimes mounts without difficulties on a Macintosh (see Thomas Tempelman's Web site for a solution to mount ISO 9660 with Joliet extensions on a Macintosh), should not be copied by extracting its files and burning them again in your favorite recording software. You should instead use the plain disk copy to make a whole copy of the contents.
The same holds true to copy a hybrid (HFS/ISO 9660) CD-ROM on a Macintosh.
Please note that, if your CD-ROM drive is of the ATAPI kind, you'll have to upgrade to version 4 of Toast to be able to copy from the ATAPI CD-ROM to the burner.
|How to copy a Macintosh or hybrid CD-ROM on a PC?
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A Macintosh CD-ROM, be it a plain HFS CD-ROM or a hybrid (HFS/ISO 9660) CD-ROM, remains a plain data CD-ROM, even if it is not conformant to the ISO 9660 standard. You should therefore use a CD-ROM copying program to do the copy. Don't use a CD-ROM burning software or a program to extract the files from the CD-ROM.
|How to mount on a Macintosh the ISO-9660 partition of a hybrid CD-ROM?
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An utility called ISOnoHFS, written by Sauro Speranza, must be launched before inserting the CD-ROM. The Macintosh then mounts the ISO 9660 partition. This utility is very useful when testing the result of a hybrid CD-ROM on a Macintosh.
The current version of this utility is version 2. Search for it from any search engine to locate a server on the Web. For an example, this link to Macinsearch was valid last time we checked (in march 2000).
This utility only works with SCSI drives. On the other hand, Thomas Tempelmann has announced that the version 2 of his Joliet extension would have this feature for all kinds of drives.
Easy CD Creator builds ISO images in mode 2 form 1, that is with sectors of 2352 bytes, where the payload (2048 bytes of data) is complemented by various fields (header, subheader, CRC/EDC, P and Q parity bytes). Note that those fields (excepted both subheaders) are empty. It seems that this behavior has roots in the past, when the first CD-ROM drives supporting multisession CD-ROMs only accepted mode 2 disks. This doesn't hold true nowadays. From all software packages we tested, EZCD is the only one which doesn't produce plain data images, or at least doesn't allow to build such images.
On the other hand, EZCD can also burn plain data images, with sectors containing only the payload, that is sectors of 2048 bytes.
To know which one the user asked it to burn, it looks for the string "CD001" in the image. According to the ISO 9660 standard, this string should be present at the beginning of the 16th sector. If the string is found at offset 32769, this must be a plain ISO data image, if not, this signature string should come a some offset further away.
If the program doesn't find this string, and depending on the exact version you're using, it refuses to burn or plainly crashes.
In other words, while we could expect from EZCD to trust the user and accept to burn any image, as long as the user says this is a data image (or even a mode 2 image, if this can be of any use), we must observe that this is not the fact.
See also next question about CD-ROM images produced by Toast on a Macintosh.
Now, we come to the images built by Toast on the Mac (which are plain data images):
A hybrid image contains an ISO catalog and a HFS catalog, both pointing to a common data pool (to keep things simple). Since there is an ISO catalog, there is also a "CD001" string at offset 32769, so EZCD is happy with it and burns the image.
On the other hand, if the image is a HFS image (to produce a pure Macintosh CD-ROM), there is no need (for Toast, or for the HFS file system in general) to do anything special just in case, and the image doesn't contains the string.
And here comes the problem: If EZCD doesn't find the "CD001" string, it refuses to burn or plainly crashes, depending on the exact version you're using.
On the other hand, that means that all other packages (if they accept to burn CD images), will happily burn Toast images, hybrid or not.
The image files created by Nero bear the extension NRG, but are strict ISO images (at least for data CD-ROMs), which can be hybridated by our Hybridator or our MacImage. You only have to type "*.NRG" in the File selection box to display Nero images and select the one you want to hybridate.
The logic of Nero is sometimes difficult to follow. If you want to build an image file, you first have to select the image recorder in the "CD Recorder" menu. Select the files you want to put in the image the usual way then launch the burning. Nero then asks for the name of the file. Type the filename and you get your image file with the NRG extension. You can't build the project first then select the result you want.
Last but not the least, Nero has some knowledge of HFS and hybrid images and, when you ask to burn a HFS or a hybrid image, displays the string "HFS" od "hybrid" in the track list.
Till recently, the Macintosh OS only displayed the short filenames (like FILE~1.DOC) of Joliet CD-ROMs.
Thomas Tempelmann released in may 2000 a free Joliet File System Extension for the Macintosh. This extension can be downloaded from his Web Site. This extension only displays the first 31 characters of the filename. More, the full name is available in the Information dialog box.
A specification was published in 1995 to describe a method to produce bootable
ISO 9660 CD-ROMs. This standard, called "El Torito", can be downloaded from
Phoenix site (Phoenix
is one of the promoters of this standard).
The principle is to put a so-called "boot entry" in the sector 17, after the
volume descriptor. This entry points to one or several bootable images (images
of floppy disks or of other media). This method cannot apply to Macintosh HFS
Andy's CDR FAQ is probably the richest FAQ on CD-ROM burning. This FAQ is regularly updated and should be visited if you have questions on those subjects.
There is a French version of this FAQ, maintained by Marc Kergomard.
Another good source of information (but much more technical, on standards, and so on) is Media Sciences CD FAQ.
One of the "features" of the ISO 9660 standard (at least, at level 1 of conformance) is that the filenames can only contain uppercase letters, digits and the underscore, and that the filename length is limited to eight characters for the name and three characters for the extension. Subfolders can only use eight characters, and there is a limit to the depth of the subfolder tree (8).
More, one of the recurrent "problems" with Macintosh files is that they can contain two so-called forks (the data fork and the resource fork).
For these reasons, Apple published Extensions to ISO 9660 to be able to keep the forks together and to manage the signatures and Finder flags, even on an ISO 9660 CD-ROM (See Technical Note FL36). When associated to the Joliet extension, those CD-ROMs even keep the long filenames.
Under Windows 95, the CD-ROM behaves normally most of the time, but accented letters are falsely displayed.
It is also possible, if the authoring software did not change the filenames containing characters which are unallowed on the PC (for an example, slashes), that you won't be able to get the data. Please note that our transfer program MacDisk manages correctly those volumes.
Three software packages can read (open) ISO 9660 images, for an example to test an image or to extract some files:
For a long time, users frequently asked about a tool to edit ISO images. Since the ISO 9660 format is a "write-only" format, no such tool was available. Recently, a new tool appeared on the Internet, WinISO
, which announces that it can convert between several image formats and even delete and add files in some image formats. We didn't have the time to test yet.
Windows Server 2003 Resource Kit contains a little piece of software called cdburn.exe to allow burning existing CD-ROM images from the command line.
It can be downloaded from the Windows Server 2003 page. Do a search for its name on Microsoft Web site if the address above becomes invalid.
The documentation states that this program only runs under Windows XP and higher. The installer refuses to install the components under Windows 2000, but the program itself runs correctly..
Alex Feinman wrote a program running under Windows XP to burn CD-ROM images and produce CD copies (CD to CD). This program (free for personal use) can be downloaded from his Web site: ISO Recorder.