[Coco] Challenge: identifying file type by sector of data

[Robert Gault]

Steve Ostrom wrote:
>>
>
> If the disk is bad, you probably are out of luck. If the sleeve is binding,
> removing the disk and spreading the edges of the sleeve and then returning the
> disk to the sleeve, will reduce the friction and the disk MAY be readable.
>
> If one or more sectors are damaged, the disk might be readable with the proper
> software. Keep in mind that some copyright schemes removed the data address mark
> from some sectors so a disk could not be backed up. A program like my Colorzap
> can restore DAMs to sectors.
>
> Robert
>
>
> Now that is really cool.  I didn't know you could restore a DAM, which should
> allow the copy routine to work.  CDM allows you to change individual bytes on a
> disk.  Can I use CDM to add missing DAM's to the disk?  Can you explain how
> Colorzap does that?  I'm very eager to hear about this.
>
> Thanks!
>
> --- Steve O ---
>
>

If you read the Western Digital "Storage Management Products Handbook 1986" 
looking for the controllers for our Coco drives, such as the WD279X-02, you will 
find Command Summary tables.
The Read Sector/Write Sector commands are a type II for which there is a 
bit-flag for Data Address Mark. ON deletes the mark. OFF adds/restores the mark.

You just need a program which will read a sector and ignore any errors thrown by 
the controller. Once read, the sector can be written back to the disk, restoring 
the DAM.

I just ran a test with my Colorzap program where I put some text in a sector and 
then deleted the DAM. I could not read the sector normally but even though no 
sector data was displayed, writing the sector back to the disk restored the DMA 
and the text in the sector became readable again.

Robert