(The 'logical block' of an ISO-9660 file system being a fairly good example, as it must be kept notionally separate from the 'logical sector' despite that it usually is the same size.)
Please explain. ISO9669 only exists on optical and optical is always 2048 bytes per block.
If we are to be very strict about it, ISO-9660 exists only on CD-ROM. That's what the standard says. But that's too strict, I think a reasonably close reading of the standard makes it clear that there's very little if anything that actually locks it technically to CD-ROM except the words used by of the standard.
If a medium with 2048-byte sectors was the only possibility, section 6.1.2 would not make sense – it defines a 'Logical Sector', and allows it to be any power of two that is at least 2048 byte. It also connects the Logical Sector Size to the size of the Data Field of the underlying medium (which is assumed to be a CD-ROM) … but it does allow the size of the Data Field to be *less* than 2048 bytes, allowing a Logical Sector to comprise multiple physical sectors.
That entire construction of Logical Sectors separates the design of ISO-9660 from the physical sector size of the media on which it is implemented. That signals 'not only CD-ROM' to me.
However, the title of 6.1.2 is 'Arrangement of data on a CD-ROM' (my emphasis). To insist that CD-ROM then is the only legal medium is possible, but needlessly strict. It prevents ISO-9660 from being used on CD-R, for example, as well as on all DVD media, and so on. Noone really wants that.
The Logical Block of ISO-9660 is defined in 6.2.2, and is allowed to be any power of two that is at least 512 bytes. I don't know of any publicly available implementation that allows the user to specify the logical block size, yet 12.3.1 explicitly requires that the data preparer should be allowed to specify Logical Block Size (among several other things).
Thus, in ISO-9660, Logical Block and Logical Sector must be kept separate. The penalty for failing to do so is very small, though – I don't know of any existing media that have different sizes.
That would be putting portability before speed, though, and that I don't really think I'll find …)
That surprises me. You'd want to format a USB stick in a format that you can move to the next (similar) OS, whether it runs on intel or motorola (for instance). So I would expect a fixed agreed on (per the specs) endianess. Again, not what I'm used to (joliet, UDF, etc.)
But UFS/FFS was designed for disks. If you wanted to exchange data with an totally unknown computer, you'd prepare a magnetic tape, using ISO 1001/ECMA 13 … or rather their precursors. If you *knew* what the receiving system was, you could use something else. But you never took a Winchester disk from one system to another unless you knew that it was exactly the same hardware and software platform.
If you had to move files between, say, a IBM PC and an Apple II, you typically used FAT-floppies – that was probably the first widely portable file system. (Though I remember that The C User's Journal made an attempt to define a CPIO-based format, using floppies as a kind of unstructured block storage. It didn't take off, as a I recall.)
That entire construction of Logical Sectors separates the design of ISO-9660 from the physical sector size of the media on which it is implemented. That signals 'not only CD-ROM' to me.
But it is. And later of course also allowed on DVD and BD, all possible because the same sector size of 2048 bytes is used.
I don't recall the specifics and don't have time to go look it up but the first spec approved for optical was derived from a more generic file system that had been developed, and that was probably not tied to a particular physical sector size, so some of the wording might still be from that original spec.
There are also no optical discs that have a sector size different than 2048 bytes.
FYI -the Apple II if my memory is correct used 13 or 16 sector, 5.25" disks that were recorded with GCR not FM or MFM. I think they had 512 byte sized sectors. The first time you could use PC 3.5" floppy was on the Mac
When you get to Reiser you will discover another interesting concept, a logical block can be shared with many files
When you get to Reiser you will discover another interesting concept, a logical block can be shared with many files
Interesting !! Like common data for all these files ?
I don't think I will fully implement Reiser soon. Too many other things to do still, but good to know.
When you get to Reiser you will discover another interesting concept, a logical block can be shared with many files
Interesting !! Like common data for all these files ?
I don't think I will fully implement Reiser soon. Too many other things to do still, but good to know.
Not common data for files, but it makes full use of would be slack space. It never wastes more than I think 7 bytes a block. A file may start in the middle of a block - normal data carving will have problems.
Not common data for files, but it makes full use of would be slack space. It never wastes more than I think 7 bytes a block
I see !!
Not much of a problem itself but indeed, for data carving it is poses a big problem.