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- Atari format support
- ====================
- Both mkdosfs and dosfsck now can also handle the Atari variation of
- the MS-DOS filesystem format. The Atari format has some minor
- differences, some caused by the different machine architecture (m68k),
- some being "historic" (Atari didn't change some things that M$
- changed).
- Both tools automatically select Atari format if they run on an Atari.
- Additionally the -A switch toggles between Atari and MS-DOS format.
- I.e., on an Atari it selects plain DOS format, on any other machine it
- switches to Atari format.
- The differences are in detail:
- - Atari TOS doesn't like cluster sizes != 2, so the usual solution
- for bigger partitions was to increase the logical sector size. So
- mkdosfs can handle sector sizes != 512 now, you can also manually
- select it with the -S option. On filesystems larger than approx. 32
- MB, the sector size is automatically increased (stead of the
- cluster size) to make the filesystem fit. mkdosfs will always use 2
- sectors per cluster (also with the floppy standard configurations),
- except when directed otherwise on the command line.
- - From the docs, all values between 0xfff8 and 0xffff in the FAT mark
- an end-of-file. However, DOS usually uses 0xfff8 and Atari 0xffff.
- This seems to be only an consmetic difference. At least TOS doesn't
- complain about 0xffff EOF marks. Don't know what DOS thinks of
- 0xfff8 :-) Anyway, both tools use the EOF mark common to the
- system (DOS/Atari).
- - Something similar of the bad cluster marks: On Atari the FAT values
- 0xfff0 to 0xfff7 are used for this, under DOS only 0xfff7 (the
- others can be normal cluster numbers, allowing 7 more clusters :-)
- However, both systems usually mark with 0xfff7. Just dosfsck has to
- interpret 0xfff0...0xfff7 differently.
- - Some fields in the boot sector are interpreted differently. For
- example, Atari has a disk serial number (used to aid disk change
- detection) where DOS stores the system name; the 'hidden' field is
- 32 bit for DOS, but 16 bit for Atari, and there's no 'total_sect'
- field; the 12/16 bit FAT decision is different: it's not based on
- the number of clusters, but always FAT12 on floppies and FAT16 on
- hard disks. mkdosfs nows about these differences and constructs the
- boot sector accordingly.
- - In dosfsck, the boot sector differences also have to known, to not
- warn about things that are no error on Atari. In addition, most
- Atari formatting tools fill the 'tracks' and 'heads' fields with 0
- for hard disks, because they're meaningless on SCSI disks (Atari
- has/had no IDE). Due to this, the check that they should be
- non-zero is switched off.
- - Under Atari TOS, some other characters are illegal in filenames:
- '<', '>', '|', '"', and ':' are allowed, but all non-ASCII chars
- (codes >= 128) are forbidden.
- - Roman <Roman.Hodek@informatik.uni-erlangen.de>
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