Removing corrupt foreign language MacOS downloads

As was recently pointed out, a number of the foreign language MacOS 7.x, 8.x, and some other Apple Macintosh downloads are actually corrupt.

I want to explain what the issue is:

These CDs and floppy disks were archived in the compressed Apple DiskCopy "NDIF" image format.

This format places critical information required for decompression in the file's resource fork.

At some point in these files history, they were extracted from a Macintosh file system or Macintosh StuffIt archives in to the PC world, and the resource forks were discarded.

Unlike ISOs or uncompressed disk sector images, discarding the resource fork of NDIF images renders them incomplete, corrupt, and unusable.

I believe these files found their way through possibly multiple archives before they found their way to Winworld. To prevent further propagation of these files and wasting time/bandwidth, I am in the process of removing them.

If anyone has fresh, original, dumps from known good media, please do contribute them.

A little more technical information:

At a glance, the NDIF file format appears to be a fairly trivial Run Length Encoded (RLE) compression. However, it places part of the compression data in a "BCEM" resource in the resource fork. This data is unique to each file, and the file can not be decompressed without this data. At a glance it sort of looks like pointer data, and the size of the resource varies with the size of the file.

The exact purpose of this data is UNKNOWN. The DiskCopy NDIF file format is proprietary and completely undocumented.

More importantly, there is no known way to recover once this data is lost. There are no known tools that will decompress DiskCopy NDIF formats without the resource fork data.

No one has stepped up to the plate to reverse engineer the NDIF format. Depending on what the resource fork data actually does, it may or may not be technically possible to reconstitute that data or decompress without. However with the lack of documentation and tools, the assumption is that it is not.

Comments

  • Ok, here are the files I have identified as corrupt NDIF images, and removed:

    Apple Mac OS 7.1 [Color Classic] (3.25).7z
    Apple Mac OS 7.1 [IIvi, IIvx] (3.25).7z
    Apple Mac OS 7.1 [LC 475, 575, Quadra 605] (3.25).7z
    Apple Mac OS 7.1 [LC 520, 550] (3.25).7z
    Apple Mac OS 7.1 [LC III] (3.25).7z
    Apple Mac OS 7.1 [Mac TV] (3.25).7z
    Apple Mac OS 7.1 [PowerBook 16x, 18x] (3.25).7z
    Apple Mac OS 7.1 [PowerBook Duo] (3.25).7z
    Apple Mac OS 7.1 [Quadra 610, 650, 800] (3.25).7z
    Apple Mac OS 7.1 [Quadra 660AV, 840AV] (3.25).7z
    Apple Mac OS 7.1.2.7z
    Apple Mac OS 7.5 [Performa 630 DOS].7z
    Apple Mac OS 7.5 [PowerMac 6100, 7100, 8100] (3.25).7z
    Apple Mac OS 7.5 [PowerPC 601 CPU Upgrade] (3.25).7z
    Apple Mac OS 7.5.1 [Apple Workgroup Server] (3.25).7z
    Apple Mac OS 7.5.3 (3.25).7z
    Apple Mac OS 7.5.3 [Bulgarian].7z
    Apple Mac OS 7.5.3 [Italian].7z
    Apple Mac OS 7.6.1 [British].7z
    Apple Mac OS 7.6.1 [French].7z
    Apple Mac OS 7.6.1 [German].7z
    Apple Mac OS 7.6.1 [International].7z
    Apple Mac OS 7.6.1 [Italian].7z
    Apple Mac OS 7.6.1 [Japanese-Kanji].7z
    Apple Mac OS 7.6.1 [Simpl. Chinese].7z
    Apple Mac OS 7.6.1 [Spanish].7z
    Apple Mac OS 7.6.1 [Swedish] (alt).7z
    Apple Mac OS 7.6.1 [Swedish].7z
    Apple Mac OS 8.0 [Arabic].7z
    Apple Mac OS 8.0 [Belgian-French].7z
    Apple Mac OS 8.0 [British].7z
    Apple Mac OS 8.0 [Bulgarian].7z
    Apple Mac OS 8.0 [Canadian-French].7z
    Apple Mac OS 8.0 [Catalan].7z
    Apple Mac OS 8.0 [Croatian].7z
    Apple Mac OS 8.0 [Czech].7z
    Apple Mac OS 8.0 [Finnish].7z
    Apple Mac OS 8.0 [French].7z
    Apple Mac OS 8.0 [Hebrew].7z
    Apple Mac OS 8.0 [Hungarian-Magyar].7z
    Apple Mac OS 8.0 [International].7z
    Apple Mac OS 8.0 [Italian].7z
    Apple Mac OS 8.0 [Japanese-Kanji].7z
    Apple Mac OS 8.0 [Korean-Hangul].7z
    Apple Mac OS 8.0 [Norwegian].7z
    Apple Mac OS 8.0 [Polish].7z
    Apple Mac OS 8.0 [Portuguese].7z
    Apple Mac OS 8.0 [Simpl. Chinese].7z
    Apple Mac OS 8.0 [Spanish].7z
    Apple Mac OS 8.0 [Swedish].7z
    Apple Mac OS 8.0 [Swiss-French].7z
    Apple Mac OS 8.0 [Swiss-German].7z
    Apple Mac OS 8.0 [Trad. Chinese].7z
    Apple Mac OS 8.0 [Turkish].7z
    Apple Mac OS 8.1 [Arabic].7z
    Apple Mac OS 8.1 [British].7z
    Apple Mac OS 8.1 [Czech].7z
    Apple Mac OS 8.1 [Dutch].7z
    Apple Mac OS 8.1 [French].7z
    Apple Mac OS 8.1 [German].7z
    Apple Mac OS 8.1 [Hangul-Korean].7z
    Apple Mac OS 8.1 [International].7z
    Apple Mac OS 8.1 [Italian].7z
    Apple Mac OS 8.1 [Japanese-Kanji].7z
    Apple Mac OS 8.1 [Norwegian].7z
    Apple Mac OS 8.1 [Portuguese].7z
    Apple Mac OS 8.1 [Simpl. Chinese].7z
    Apple Mac OS 8.1 [Spanish].7z
    Apple Mac OS 8.1 [Swedish].7z
    Apple Mac OS 8.1 [Trad. Chinese].7z
    Apple Mac OS 8.1 [Turkish].7z
    Apple Mac OS 8.1 [Ukranian].7z
    Apple Mac OS 8.5 [Dutch].7z
    Apple Mac OS 8.5 [Finnish].7z
    Apple Mac OS 8.5 [French-Universal].7z
    Apple Mac OS 8.5 [German].7z
    Apple Mac OS 8.5 [Hangul-Korean].7z
    Apple Mac OS 8.5 [Italian].7z
    Apple Mac OS 8.5 [Japanese-Kanji].7z
    Apple Mac OS 8.5 [Norwegian].7z
    Apple Mac OS 8.5 [Simpl. Chinese].7z
    Apple Mac OS 8.5 [Spanish].7z
    Apple Mac OS 8.5 [Swedish].7z
    Apple Mac OS 8.5 [Trad. Chinese].7z
    Apple Mac OS 8.6 [British].7z
    Apple Mac OS 8.6 [Danish].7z
    Apple Mac OS 8.6 [Finnish].7z
    Apple Mac OS 8.6 [French-Universal].7z
    Apple Mac OS 8.6 [German].7z
    Apple Mac OS 8.6 [Hangul-Korean].7z
    Apple Mac OS 8.6 [International].7z
    Apple Mac OS 8.6 [Italian].7z
    Apple Mac OS 8.6 [Japanese-Kanji].7z
    Apple Mac OS 8.6 [Norwegian].7z
    Apple Mac OS 8.6 [Simpl. Chinese].7z
    Apple Mac OS 8.6 [Spanish].7z
    Apple Mac OS 8.6 [Swedish].7z
    Apple Mac OS 8.6 [Trad. Chinese].7z
    Apple Mac OS 9.0 [International].7z
    Apple Mac OS 9.0 [Swedish].7z

    I have also marked the downloads to indicate if they are a proper ISO or a "hard disk image". It was common for Macs to store CD images with only the Mac file system. Some CD burners programs still know how to handle these. These can also be mounted as a hard drive on an emulator. Long term, these probably need to be converted or redumped.

    I also noted a few as "bad?" that looked like valid CD ISO images but would not open in ImgBurn. These are probably fixable, and might work in other CD burners.
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