Mistach * Warning on 3.5'' IBM PC Disk

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nightson
Posts: 3
Joined: Sat May 19, 2018 11:37 am

Mistach * Warning on 3.5'' IBM PC Disk

Post by nightson » Wed Dec 05, 2018 1:52 pm

I was dumping the 3.5'' Upgrade Disk for Muzzle Velocity and encountered this error. Does it mean there is data on that sector that was not dumped correctly? By the way, I tried the mount the img image in DOSBox. The files can be copies without any error but I did encounter an error while trying to install the upgrade.
2018-12-05_203927.jpg
2018-12-05_203927.jpg
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MUZZLE_UPGRADE_1.23.log.7z
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SomeGuy
Posts: 178
Joined: Wed Feb 18, 2015 8:18 pm

Re: Mistach * Warning on 3.5'' IBM PC Disk

Post by SomeGuy » Wed Dec 05, 2018 3:01 pm

In this case you have encountered an extra mastering information track. Some disk mastering systems write an extra track on track 80 (or 40 for 48tpi disks, and remember this is counting from zero) that contain information such as a the time the disk was written, the name of the software, and the the ID of the mastering device. This is usually in a non-standard sector or encoding format. This is not used at all by whatever software is on the disk.

The thing is, when dumping to an IMG file, you actually DO NOT want to include this data. In this case you are dumping a 1.44mb disk. You want your IMG file to be exactly 1,474,560 bytes. Having extra data on the end can confuse some imaging tools or emulators, although many just ignore extra data.

If your image is slightly larger than 1,474,560 bytes then you may need to tell the Kryoflux to stop dumping at track 79.

If it is already exactly that size, then the Kryoflux did omit the sector - but you don't need it.

nightson
Posts: 3
Joined: Sat May 19, 2018 11:37 am

Re: Mistach * Warning on 3.5'' IBM PC Disk

Post by nightson » Thu Dec 06, 2018 3:14 pm

SomeGuy wrote:
Wed Dec 05, 2018 3:01 pm
In this case you have encountered an extra mastering information track. Some disk mastering systems write an extra track on track 80 (or 40 for 48tpi disks, and remember this is counting from zero) that contain information such as a the time the disk was written, the name of the software, and the the ID of the mastering device. This is usually in a non-standard sector or encoding format. This is not used at all by whatever software is on the disk.

The thing is, when dumping to an IMG file, you actually DO NOT want to include this data. In this case you are dumping a 1.44mb disk. You want your IMG file to be exactly 1,474,560 bytes. Having extra data on the end can confuse some imaging tools or emulators, although many just ignore extra data.

If your image is slightly larger than 1,474,560 bytes then you may need to tell the Kryoflux to stop dumping at track 79.

If it is already exactly that size, then the Kryoflux did omit the sector - but you don't need it.
Thanks for your detailed explanation! Glad to know the disk is good. Is there a way to view the information on that track?

SomeGuy
Posts: 178
Joined: Wed Feb 18, 2015 8:18 pm

Re: Mistach * Warning on 3.5'' IBM PC Disk

Post by SomeGuy » Sat Dec 08, 2018 12:41 am

Well, if you set the kryoflux's decoding sector size to 128 bytes (might be 256 or 1024 bytes, but 128 is common) and then tell it to just MFM decode that track, it should create a file with the sector's data. Note that these sectors often have an intentionally bad CRC.

Sometimes for exploring oddball bits of geometry like this, I find the HxC disk tool software useful. With that I can see a graphical plot of the disk layout, don't have to specify sector size or FM/MFM encoding (but as a result, it can be a bit slow), and it shows a preview of the selected sector's data. (Note that is a third party product and the Kryoflux staff do not provide assistance with that)

These mastering info tracks are not always in a standard encoding, but often they are in an FM or MFM sector that these tools will let you see.

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