> > PS: The hp disktab says that the disk has/uses/supports? ZBR.
> >     Does anyone know this 'feature'?
> 
> I believe ZBR is just a method of encoding information on the disk, like 
> RLL and MFM.

ZBR is Zoned Bit Recording; it's a data layout policy, not a 
recording/encoding mechanism.  The disk is divided up into different zones, 
and outer zones have more sectors per track than inner zones.  According to my 
cheat sheet:

#       start	end	sect/	cyl	track
#	cyl	cyl	track	skew	skew
$DiskMechanismDataArray(QuantumPD425S).setZones { 
	{0	189	78	38	22} 
	{190	379	73	36	21} 
	{380	569	68	34	19} 
	{570	759	64	31	19} 
	{760	949	59	29	18} 
	{950	1139	54	28	16} 
	{1140	1329	49	25	15} 
	{1330	1519	44	23	14} 
};

In other words, the outer tracks have nearly twice as many sectors as the 
inner ones.

-richard