Re: SCSI Hard Disk Limitations

[dempson@actrix.gen.nz (David Empson)]

David Empson <dempson@actrix.gen.nz> wrote:

> If you go up to an 80 MB partition, HFS uses three disk blocks per
> allocation block.
> 
> At 512 MB, HFS uses 16 disk blocks per allocation block (8 KB).
> 
> At 1 GB, HFS uses 32 disk blocks per allocation block (16 KB).
> 
> At 4 GB, HFS uses 128 disk blocks per allocation block (64 KB).
> 
> (etc.)

One other point I was intending to mention: HFS is better than the
MS-DOS FAT16 file system in this area, because HFS supports allocation
block sizes which conist of any integer number of disk blocks (1, 2, 3,
4, 5, 6, 7, 8, ...).  FAT16 only supports cluster sizes which consist of
a power of two number of disk blocks (1, 2, 4, 8, 16, 32, 64, 128, 256,
512, 1024, etc.)

This means that HFS scales more smoothly than FAT16 for larger volume
sizes.  FAT16 has a sudden doubling of the cluster size if you increase
the partition size beyond a point where the smaller clusters can be
used.

(HFS+ and FAT32 both solve these problems by allowing more allocation
blocks per volume, by using 32-bit allocation block numbers instead of
16-bit.)

-- 
David Empson
dempson@actrix.gen.nz