On Tue, 12 Oct 1999, Bob Nestor wrote:

> Besides, I see that the next version of Apple's Disk Setup that comes 
> with MacOS 9 is supposted to allow one to setup UNIX partitions.  Maybe 
> it will replace Mkfs for us.

Hrm, maybe not. MacOS 8.1 is the last system that runs on 68k macs.
 
> >> It's been some time since I looked at that section, but as I recall 
> >> it gets this value from the drive itself by doing a Mode Sense. 
> >> That's why some have reported in the past that they were unable to
> >> use certain disks with NetBSD because they were originally
> >> formatted for block sizes other than 512.
> >
> >I seem to recall there's some kind of trickery involved in getting the
> >geometry with a Mode Sense. You get different values depending on how
> >you've set the "Notch" first: notch 0 for the whole drive synthetic
> >geometry, notches 1 - ? for actual values. FWB Hard Disk Toolkit
> >returns the notch 0 value by default; maybe Mkfs does it different,
> >i.e. _wrong_?
> >
> As I recall there are four different sets of values, Default, Active, 
> Current, and one other that seems to be media related.  When I played 
> with them on all the disks I have I wasn't able to find any differences 
> between the four sets.

That's not exactly what I mean. Are you familiar with 'FWB Hard Disk
Toolkit'? It includes an application, SCSI Control (?), that lets you
edit and recall mode pages individually. There's one page, I forget
which, which has the notch and geometry. Depending on what you _write_
in the notch (or "zone") field, what you _read_ in the
sectors/cylinder changes. This represents the changing geometry for
the different zones on the drive. NetBSD disklabel, FWB's "get
geometry" command, and other MacOS utilities return the value of zone
'0', which is a "fake" zone that represents the average for all zones.
I seem to recall Mkfs returns the value of zone '1'.

I realize it's mainly a curiosity, as we don't seem to use CHS
addressing for anything. Maybe something to do with the wierd 
sector size, maybe not.

As for the different sets, most of the drives I've played with have
differences between Current and Default. The FWB formatted drives have
quite a few. The AHC-SCSI firmware formatted Seagates on my 486 PC's
didn't have any differences (as viewed with a Seagate DOS utility)
until I turned off the power-saver (with another Seagate utililty).