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    SubjectRe: [PATCH] zip drives
    On Wed, 15 Mar 2000 wrote:

    > Gadi Oxman writes:
    > > Another point to add is that some (newer?) ZIP drives have a jumper
    > > on them which enables some cheat mode for MSDOS which actually hides
    > > some sectors from the device driver. That is, block 0 on the drive
    > > actually moves along with the partition table, and perhaps also the
    > > reported capacity.
    > Yes, very good! [It wouldnt be the PC disk drive industry
    > if there weren't some fake and double-fake involved..]
    > That explains all reports seen so far concerning size,
    > geometry, partition table and "FAT bread failed" stuff.
    > Yesterdays description must be modified:
    > 100MB disks have a capacity of 100663296 bytes, i.e., 196608 sectors
    > and the 100646912 bytes (196576 sectors) commonly seen is because
    > the first 32 sectors are hidden.
    > The hiding is done on some models, not on early models
    > and not on the very latest either, and that explains why
    > people report that a disk that is fine on one machine
    > contains garbage on another, and when written on the other
    > looks like garbage on the first again.
    > The hiding removes the first track including the MBR with
    > partition table. This explains how it can happen that the
    > same disk has to be mounted as /dev/sda on one machine
    > and as /dev/sda4 on another.
    > I'll put this info on some web page.
    > Maybe we should teach the kernel some of this stuff
    > so that a poor innocent user doesnt have to struggle.
    > [Detailed proposals for desired kernel behaviour are welcome.]

    Load first sector. Is it an MBR/partition table, or a boot sector?
    If the former, add an offset of 32 sectors to all subsequent accesses.
    This way, we get consistent behaviour from both types of drive.
    You then always mount /dev/sda (or whatever).

    (Alternatively, if there is some way of "unhiding" the first 32 sectors
    reliably, we should do that - is it possible??)


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