[Coco] large HD in OS9/68K

[Gene Heskett]

On Thursday 13 November 2003 22:08, David wrote:
>On Thu, Nov 13, 2003 at 09:02:36PM -0500, David Hazelton wrote:
>> Dave Kelly wrote:
>> >>>My MM1 drive is set to 33 spt starting with sector 0. So that's
>> >>> 0 - 32.
>> >>
>> >>I wonder if there's any valid reason for starting with sector 0?
>> >>  It's apparently an odd setup.
>> >
>> >Zero is the first number.
>> >It is my understanding that machine language and the C language
>> > uses 0 as the first number.  OS9 follows this convention.
>
>Coco OS9 started with 1.  I don't know whether this was MW's doing
> or Tandy's.  But it appears that most of our OSK machines start
> with 0.
>
>> I thought that Microware used the Universal disk format that
>> started at track 0, sector 0 single density. but later modified
>> this due to some Disk controllers could not do this, thus the
>> Sector/Track offset in the descriptors.  Which I would believe
>> those offsets would both be set at 1 by default, so every
>> controller could deal with it.
>
>Is it the controller or the OS?  What brought this subject up was
> the fact that I couldn't read the disks on my Linux system using
> fdutils. From the documentation I found, a stock Linux kernel
> cannot read a 0-based sectored disk.  There was a kernel patch
> which I applied, but still couldn't do a raw disk copy  (dd -
> similar to "mergd /d0@ > somefile" in os9).  However, what I read
> seemed to imply that you would still have to maybe do a low-level
> sector-by-sector or maybe track-by-track read or write, so I didn't
> fool with it anymore.
>
>> Maybe this was
>> after done after the original MM1 version of the OS.  I have not
>> looked at the settings on the AT306, but on a VME machine running
>> V2.4 I did look at this as more of a confirmation of what I was
>> reading.
>
>The AT306 begins with sector 1 ?  I'm seriously considering redoing
> all my disks to begin with sector 1.  From what I can garnish,
> these 0-sectored disks are unreadable on a Linux system (not sure
> about windows), without jumping through difficult hoops.  I'd like
> to create disk images and store them on on CD to preserve them.
>
>I could do a "merge /d0@ > file" on my OSK system, then transfer
> these images to my Linux box and burn them to CD like that, but I
> still couldn't restore the floppy under linux, and if I lost the
> ability to boot on my OSK system - and these floppies are quite
> unreliable nowadays - and I'd be out of luck.
>
>But I wonder - would my boot rom be able to read a 1-based sector
> disk?
>
>Might need to check that out.

I'd doubt it.  The os9 rbf's I've delt with are all married to the 
data from LSN0 on the disk.  That said, I suppose that an fdc that 
didn't know what a zero written to its secter table register was does 
exist, in which case they would have to swap fdc's, or rewrite those 
portions of os9 as appropriate.  Since the hard drive was treated the 
same in that regard, it really doesn't make a lot of sense (to me) 
that an fdc would be so limited.

-- 
Cheers, Gene
AMD K6-III at 500mhz 320M
Athlon1600XP at 1400mhz  512M
99.27% setiathome rank, not too shabby for a WV hillbilly
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Copyright 2003 by Maurice Eugene Heskett, all rights reserved.