Re: floppy disk change (was Re: 1.15 kernel)

[Konrad Kokoszkiewicz <draco@mi.com.pl>]

> > BTW. I always had troubles understanding why there are so many problems
> > with floppy disk change (or media change in general, but it beats me
> > considering floppies) on ST/TT/Falcons. Is there any reason for not using
> > the most simple solution, as re-reading the bootblock and updating the
> > internal filesystem data strucres accordingly (like clearing FAT or inode
> > caches for example), if the bootblock differs from what was read before?
> 
> No.
> 
> However, you should only do this if you think the disk *might* have changed.
> 
> The disk change on older STs works quite fine, and Falcon and newer machines
> have hardware disk change detection which can tell you 100% sure if the disk
> was removed from the drive (it can't tell you if the same disk was
> re-inserted, so you should check and *not* clear open files etc. in that
> case).

A very nice theory, but it has actually nothing to do with the practice.
Actually your "100% perfect hardware disk change detection" can only
detect if a floppy is changed, if the floppy (or both floppies you swap in
the drive) are write protected. If both are writable, the TOS 3.06 will
tell you 100% that no change took place, no matter how many times you
really changed the disk.

> > Actually, any disk operation, like opening a file for read/write/update or
> > reading directories could cause bootblock to be re-read by the system. 
> 
> Why?

To not screw up the filesystem on a changed diskette when you copy
something to it while the system doesn't even know you changed it. Which
occurs actually quite often (or: would if you weren't aware that disk
change detection is broken in most ataris).
 
> This is absolutely unnecessary and will cause a lot of extra seeks to track
> 0. Just think about copying a lot of small files from floppy to harddisk
> ...
> 
> > Then we have the serial number there, the volume name and the number of
> > free clusters to check if the diskette is still the same. Perhaps it will
> 
> Number of free clusters? In sector 0?

Yeps. Where you'd exspect number of free clusters?

> TOS uses a checksum for sector 0-6 (IIRC) to decide if the disk was really
> changed or not. Sector 0 alone is not a sure indication, as it may be
> identical on different disks.

Yes, I know the theory about TOS behaviour (I read the doc for FLOPFIX).
The problem is that it DOES NOT WORK. And it is quite unlikely for the
sector zero to be identical on two diskettes (each has 32 bit random
serial number generated while formatting).

> Why not use the hardware to tell you if the disk drive door was opened or
> not?

Hardware? Why to build a hardware, if it may be solved by software?

> > a) floppies aren't the main storage media anymore (harddisks are)
> 
> Floppies are still used for data transfer - and they are slow already, so
> there is no need to slow it down even more unnecessarily.

One more seek to track 0 doesn't hurt anything; I am even not sure if it
would cause an additional seek, because track 0 is read anyways (the FAT
is on the track 0).

> > b) this perfectly works for SpartaDOS on 8-bit Atari, though XL serial
> >    drives are 10 times slower than our floppy drives. I have no reason
> >    to not using a working solution from 8-bit computers, if such a
> >    solution works.
> 
> It may work, but is it a good and efficient solution? I don't think so.

You may think anything you want, but you didn't see that it really worked.
I saw both solutions in action, hence I know what's more efficient.
Actually all that behaviour of ST series (considering floppy disk changes)
I find as one of the most sad things in TOS boxes in daily usage.

Gtx,

--
Konrad M.Kokoszkiewicz
|mail: draco@mi.com.pl                  | Atari Falcon030/TT030/65XE |
|http://www.orient.uw.edu.pl/~conradus/ | ** FreeMiNT development ** |

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