[hfs-user] Floppy formatting

Patrick Dirks pwd@apple.com
Thu, 26 Sep 2002 16:28:56 -0700

On Thursday, September 26, 2002, at 09:01 AM, Pierre Duhem wrote:

> Bonjour Simon,
> Le jeudi 26 septembre 2002, à 17:21, vous écriviez :
> SB> Note thought that under HFS+ blocks size can be changed. Under HFS
> SB> it MUST be 512bytes.
> I don't think this is true. My formatter computes the block size with
> a simple division: 1 + (nb_sectors / 0xFFFF). I think I found this
> formula on some Apple document (Inside Macintosh ?).

Um, not sure exactly what you're trying to do but this could be 
trouble.  On HFS the allocation block size was, by default, the 
smallest multiple of 512 bytes that would make the total number of 
allocation blocks fit in 16 bits.  On HFS+, however, the allocation 
block size must be a power of two multiple of 512, i.e. 512 bytes, 1K, 
2K, 4K, 8K, etc.  3K, for instance, would NOT be a valid allocation 
block size!

See TN1150 (bottom of page 4).

> SB> Changing it means its not a HFS disk anymore.
> SB> Perhaps HFS+ requires a partition table. Have a read of Technote
> SB> TN1150 for more information (regarding HFS+)
> I read TN1150 several times along the years, from one of the first
> editions, in 1999. I didn't read anything about the need of a
> partition table. That is what one should conclude from reading IM and
> other documents, but it is never stated so clearly. On the other hand,
> I already saw many such media.
> -- 
> Best Regards
> Pierre Duhem
> Logiciels & Services Duhem, Paris (France)
> duhem@macdisk.com