[hfs-user] Partition and Boot block Structures in a HFS CD image

Mark Day mday@apple.com
Tue, 26 Feb 2002 10:12:47 -0800

On Tuesday, February 26, 2002, at 06:51  AM, Simon Bazley wrote:

> I'm not sure about the partition stuff, Floppy disks don't need
> partition info, so I'd guess you don't need it on a CD either, but I may
> be wrong.

I don't think you need the partition map as long as the volume isn't 
bootable, but I'm not absolutely certain.  I don't happen to have any 
partitonless CDs lying around since all the ones I have are bootable.

> Both HFS and HFS+ state that the MDB (or VDB) must reside at sector 3
> (sector 2 if you start with 0) and that sectors are 512 bytes.
> The bit before that should contain the device driver, for the hard disk,
> which I'm assuming will be ignored if its all zero's (and hence not
> bootable).

Actually, that first 1024 bytes isn't a device driver.  When it is 
non-zero, it contains code and data that the Mac OS ROM would use to 
boot from that volume.  Filling it with zeroes ensures that the Mac OS 
ROM won't try to boot from it.

Device drivers, if any, would actually go in separate partitions whose 
type tells the system that the partition contains a driver.