Talk:ISO 9660/Archive 2

Limit on number of directories
I'm not sure I agree with the article, which states that there is a limit on the number of directories, imposed by the restriction of the field 'Parent Directory Number' (9.4.4) to 16 bits. The reasoning seems to be that if a directory produces a path table entry that (in theory) would get a Directory Number (though never explicitly recorded) > 65535, it is not permitted to exist.

Main objection: There is no explicit limit of the number of entries in the Path Table, only that the Path Table can't exceed 2^32-1 bytes. This appears to allow any number of entries as long as their *Parent Directory* Number fits in the 16-bit limit. That is, as long as the number of directories in level 1..7 don't exceed 65535, one additional level of directories can be accommodated without breaking either the word or the data structures of the standard.

Additionally, a Path Table is expected to contain entries also 'for those volumes of the Volume Set the sequence numbers of which are less than, or equal to, the assigned Volume Set size of the volume.' That is, the Path Table is expected to cover multiple volumes. It could be very awkward for a publisher to publish monthly volumes of an annual volume set, and find in October or so that the path table is full, and that no new directories may be created in that Volume Set.

A possible interpretation is that the Path Table is an auxiliary structure, intended to speed up access to directories that fit within it, but the reader application must always be prepared to fall back to normal file tree walking when a directory is not found in the Path Table. As the file tree must cover also earlier volumes in the set, all paths within that volume would be resolvable by referring to the last volume only, even if actual access might require changing to an earlier volume CD-ROM. The objection to this is that the standard text does not say so, either. Chapter 12 would have been the right place to allow for the data preparer to select path table contents, but I find nothing like that. I suggest dropping this section altogether, as I think it overstates the situation. Or am I missing anything?Athulin (talk) 12:07, 30 December 2015 (UTC)


 * Given that there is at least one implementation that fails without a path table (DOS), your wish does not look helpful. Schily (talk) 14:08, 30 December 2015 (UTC)


 * I don't see the relevancy of that. I'm not saying that path tables can be omitted, I'm saying that there's no clear ground for saying that the 16-bit size of Parent Directory Number is an implicit restriction on the number of directories allowed within a Volume Set.Athulin (talk) 10:09, 1 January 2016 (UTC)