MacBinary Format

Summary: MacBinary Format. What is this standard? MacBinary files and the forks composing the Macintosh files. How to manage multiple streams in a single container.

MacBinary Files

The MacBinary de facto standard allows to keep together both forks of Macintosh files on telecommunications lines or on servers which don't know anything about forks. A MacBinary file (SEA archives are a special case) contains three parts:

When you download a Macintosh file from a server, be it a data file, a program file or an archive, you generally download a MacBinary file (See also our page on binhexed files). If you download to a PC, you have to manage the parts and put them where they belong.

Reinstalling a MacBinary File on a Macintosh Volume

The procedure to reinstall the MacBinary file on a Macintosh medium is pretty simple. Here are the instructions for using our MacDisk program to transfer the file to a Macintosh HD floppy disk. The principle is the same for other media with the other tools.
1. Take a Macintosh floppy or format one with MacDisk (remember you can make a quick reformatting on a clean 1.44 MB PC diskette).
2. Select the Binary Copy mode in the 'Expert' menu (this menu should be validated in the 'Options' menu). This is not necessary under version 6, because MacDisk automatically detects MacBinary files.
3. Click on the 'PC to Mac' button.
4. Select the file in the dialog box and start the copy.
You will note that the file, on the Macintosh medium, doesn't have necessarily the same name as on the MS-DOS medium. That is because the original filename was stored in the Finder header and our program restored it. You will also observe that a part of the file was put in the data fork and another part in the resource fork.
If you mount the medium on a Macintosh, you should get a double-clickable application. Double-click on it. The Finder launches it and it executes its task, e.g. extracting the data from the archive.

Managing MacBinary Files on the PC

1) Creating a MacBinary File
It can be useful to create a MacBinary file on the PC, for an example if you have to send a file to a Macintosh user who is not fully aware of all the aspects of the creator and file type signatures (see also our page on signatures to go further on this subject). For an example, it is now well known that Quark Xpress can't open files which doesn't have a PC correct extension (QXD or QXT) or a correct Macintosh file signature (XDOCXPR3 or XTMPXPR3).
If you think that the file you have to send will be received in a program managing the MacBinary header and that you are the knowledgeable person of the two, it can be useful to "forge" a Macbinary file on your PC and send it in this form.
We posted on this site a free utility, named MacBinary, to do just that. Feel free to download it. We don't think there are very much utilities of this kind. You are free to edit the internal table of the program (use the SignEdit utility at this end).
2) Stripping the Macbinary Header
You also can do some work on the PC if your Macbinary only contains data, or only contains resource. Let's say that you have downloaded a data file from a Macintosh server. This file can be a text file, or a picture, in a format like TIFF, JPEG, etc. When those files are mostly targeted at Macintosh users, they arestored as MacBinary files. Macintosh communication programs, most of the time, strip automatically the Macbinary header.
When you download these files on a PC, you have to strip the Macbinary header to be able to get at the data. There are several utilities available to do that (just scan your favorite search engine with MAC and HEADER keywords). Our MacBinary utility is only one of them. You should nevertheless know that the trade secret is not just stripping the first 128 bytes of the file. Indeed, the real know-how is being able to identify the false, so-called MacBinary files which could be something else (to avoid corrupting files).

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