[Coco] error 249

[Stephen H. Fischer]

----- Original Message ----- 
From: "Gene Heskett" <gheskett at shentel.net>
To: <coco at maltedmedia.com>
Sent: Saturday, March 18, 2017 9:49 AM
Subject: Re: [Coco] error 249


> On Saturday 18 March 2017 11:01:18 Stephen H. Fischer wrote:
> 
>> It has been many years since I last used my real CoCo and made the
>> mistake of inserting a NitrOS-9 DNS=3 formatted disk into a drive that
>> had a descriptor set to DNS=1. Actually VCC and other emulators
>> running NitrOS-9 can demonstrate the error.
>>
>> I think that 249 was the error reported. My OS-9 manuals are currently
>> unavailable.
>>
>> I rarely used DNS=1 as all my descriptors normally had DNS=3 for my
>> 5-1/4" 80T2S disks (NitrOS-9 will double step to read a 40T2S disk.)
>> All most all of my disks I have archives of online have that format.
>>
>> I needed to use the correct DNS=3 in my system but the CoCo world
>> mainly has DNS=1.
> 
> This is one of the changes Robert G. and I did to Nitros9 a couple, maybe 
> 3 years back. Or possibly an interim change. What I wanted to do was 
> make a 40 track disk inserted into an 80 track drive into a read-only 
> disk automatically in order to protect the disk from being trashed by 
> the write of a much narrower track in the middle of its wider 40 track 
> magnetic pattern.
> 
> This of course only works IF the disks format truly reflects the disk 
> characteristics. That, _everybody_, means ALL your 5.25" 40 track disks 
> were formatted with dns=1, and ALL you 5.25" 80 track disks were 
> formatted with DNS=3.

I like your and Robert G.'s change, not everyone is as careful as I was back ~ 1990.

That change would have been problematic for me when I created disks for the local CoCo Software Collector (Thief) who only had 40T2S drives.

I used the tape demagnetizer first on the floppy and there were no problems reported for 40T2S disks created in my 5-1/4" 80T2S Teac drives.

Any of his floppies got a write protect sticker and were copied to a 80T2S floppy quickly so no writing was ever done. Each floppy format had a different color, Brown was 5-1/4" 40T2S.

SHF