[Coco] Sierra Xmas 86 demo

[Stephen H. Fischer]

Hi,

If 3.5" disks are 135 TPI and must be marked 48 TPI then I was really was 
not understanding the OS-9 documentation.

And that explains all the problems I am having trying to read my 80T2S disks 
on emulators.

If one of my 80T2S disks was written in a 5.25" drive then it must be marked 
96 TPI.
But if it was written in my 3.5" drive then it must be marked 48 TPI.

Wait, I have identical copies, one written in the 3.5" drive and one written 
in the 5.25" drive. Having the same names. YES, ~ 150 disks for each format, 
5.25" and 3.5".

Plus my switch that interchanged /D0 and /D1 was EVIL itself.

I often switched the drives and put a duplicate system disk into the new 
/D0.
I remember very few problems, making sure that the drives had stopped 
spinning first.


Yes, I accept that 80T2S disks have problems writing 40T2S disks.

I was well aware of the problem but did not experience it because I used a 
bulk tape eraser first ALWAYS.

Reading was no problem as OS-9 knew what to do with a 40T2S disk in a 80T2S 
drive.

SHF

----- Original Message ----- 
From: "Gene Heskett" <gheskett at wdtv.com>
To: <coco at maltedmedia.com>
Sent: Sunday, December 09, 2012 9:37 PM
Subject: Re: [Coco] Sierra Xmas 86 demo


> On Monday 10 December 2012 00:15:39 Stephen H. Fischer did opine:
>
>> Hi,
>>
>> What should DNS be for my 80 Track 2 sided 5.25" Disks?
>>
>> If you look at the definition for 3.5" disks, the DNS should be DNS = 3.
> NO!  not for a 3.5" disk,
>>
>>  I had A 80T2S 3.5" drive and a 5.25" 80T2S which I swapped /D0 and /D1
>> with a switch.
>
> Bad show, see below.
>
>> But most people having only 3.5" 80T2S drives might well have DNS =1.
>
> Which is 100% correct.
>>
>> What a mess Charlie Brown. Your rule "It should dns=3 for 3.5 and dns=1
>> for 5.25" just does not work.
>>
>>
> That is NOT how it works Stephen.  This whole dns tomfoolery was because
> 5.25" drives came in 48 tpi for DS40 (360k) disk drives, and 96 tpi for 
> the
> 80 track (720k) drives.
>
> DNS=03 is ONLY for use against 80 track 5.25" disks.  The idea being that
> should a 48 track disk be inserted into the 96 tpi disk drive, and the
> driver finds a DNS=01 disk in this drive when the drive descriptor is set
> DNS=03, it is smart enough to double step the drive and thereby READ that
> 40 track disk in the 80 track drive.
>
> DO NOT, REPEAT, DO NOT EVER WRITE to that disk, it will be trashed beyond
> recovery because the 96 tpi head doesn't cover the full track width,
> leaving scrambled data behind.  One can occasionally rescue the data by
> backing it up to a real 48tpi drive from that drive, but unless that 80
> track drive is spotlessly clean & well lubed so the head placement is very
> repeatable, the chances aren't great.
>
> This one item I have been thinking about fixing, because when the wide
> track diskette is put in the narrow track drive, in addition to double-
> stepping the drive, the driver is a ducking fummy for not also setting 
> that
> disk as write protected, thereby preventing such disasters.  That might be
> one of my projects this winter.
>
> 3.5" drives have only one track density, 135 tpi, so there is not a double
> track density available, so ALL 3.5" drive descriptors should be set for
> DNS=01.
>
> Cheers, Gene
> -- 
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> My web page: <http://coyoteden.dyndns-free.com:85/gene> is up!
> Intel Inside, Idiot Outside.
> I was taught to respect my elders, but its getting
> harder and harder to find any...
>
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