On Wed, 15 Mar 2000 Andries.Brouwer@cwi.nl 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??)
James.
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This archive was generated by hypermail 2b29 : Wed Mar 15 2000 - 21:00:30 EST