MFM Scatter Issue Identification

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ross-spencer
Posts: 5
Joined: Wed Apr 10, 2013 5:32 am

MFM Scatter Issue Identification

Post by ross-spencer » Wed Feb 15, 2017 4:56 am

HI All,

Two questions:

1) I know this site really well and enjoy the troubleshooting section: http://goughlui.com/2013/04/21/project- ... -practise/

But I was wondering - has anyone produced a bigger guide to help users identify the meaning of certain scatter plots?

2) Failing that, I have a disk with the following scatters - can anyone help me describe what the pattern might mean?

1-att2-example-1.PNG
2-att2-example-2.PNG
3-att2-example-3.PNG

SomeGuy
Posts: 87
Joined: Wed Feb 18, 2015 8:18 pm

Re: MFM Scatter Issue Identification

Post by SomeGuy » Wed Feb 15, 2017 5:49 am

Unfortunately, a scatter plot only tells a small part of the story. That suggests you have a disk with 15 sectors per track. And the first one looks like there might be damage on one sector. The last one sort of suggests empty sectors. Just from screen shots, I can't even tell if it is high or low density. You really need to have some context about where this disk came from.

That said, try opening the resulting image in the HxC disk utility. If it is a common low-level format, it will automatically try to decode what is there (with the KF you need to know sector sizes in advance, but not with HxC). If it can, then you can view the contents of the sectors to get more information. It will also give you a very pretty disk view, showing the layout of the sectors on the disk and any bad areas.

ross-spencer
Posts: 5
Joined: Wed Apr 10, 2013 5:32 am

Re: MFM Scatter Issue Identification

Post by ross-spencer » Wed Feb 15, 2017 7:07 am

I've a bit more on the label here if it helps.
Attachments
IMG_7923.JPG

SomeGuy
Posts: 87
Joined: Wed Feb 18, 2015 8:18 pm

Re: MFM Scatter Issue Identification

Post by SomeGuy » Wed Feb 15, 2017 3:47 pm

Ok, so it is a high density disk. That also means in all probability it is IBM PC 1.2mb formatted (15 sectors, 512 byte sectors, 80 tracks, double sided, MFM encoding)

So set the KF to decode MFM, and make sure the "density line" menu option is set to "low" (density line low means high density on most 1.2mb drives - check the manual for your drive to ensure that is correct).

If it still won't decode it, save just a "Preservation Stream" instead, and throw it at the HxC disk tool:
http://hxc2001.com/download/floppy_driv ... r_soft.zip

ross-spencer
Posts: 5
Joined: Wed Apr 10, 2013 5:32 am

Re: MFM Scatter Issue Identification

Post by ross-spencer » Thu Feb 16, 2017 12:41 am

That helped a lot. And I reduced the RPM of the read too, and we have a better result today. I not have a .img file that i can view in a hex editor. Mounting the disk didn't show any files but it worked and I can use the hex to understand what's on there.

Is there anything else these image might help to tell us about what to do next? Or indeed, the quality of the data to expect?
unread-ex.PNG
h-ex.PNG
green-ex.PNG

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