Issues duplicating 8" floppies

[joshd]

Hi all --

I'm attempting to archive and duplicate 8" floppies from various machines. I know it's not technically supported (the manual states that it *should* work but has not been tested, etc.) The disks I'm reading are nothing exotic (They're standard double-density, double-sided disks with an IBM format -- I could use a PC and ImageDisk to do the job, but the SuperCard is very convenient, if only it worked in this application ).

Thus far I've been successful in creating images of floppies, but have had no success in writing them back out. For drives, thus far I've tried a pair of Shugart 851s and a Qume QumeTrack 842. I'm using a DBit FDADAP (http://www.dbit.com/fdadap.html) to deal with cabling and the TG43 (higher write current on inner tracks) signals. (And the 851s are jumpered properly for the TG43 signal, as far as I can tell). I've also tried a variety of media (Verbatim, Maxell) with the same results (though the position of the bad data varies from attempt to attempt).

The issue is that upon reading back a disk that has been duplicated via the SuperCard, data is fine up until about cylinder 60 at which point bad sectors start appearing more and more frequently (though the vast majority of the data is still read OK). I tried disabling TG43 just to see if it made a difference, and it does - with TG43 disabled sectors written past cylinder 43 read back as garbage. (So at the very least, the TG43 write current select line is being correctly set by the FDADAP board).

I discussed this issue with the kind folks on the cctalk mailing list and they suggested that perhaps the SuperCard Pro isn't providing the write precompensation needed for these older drives. I cannot find any mention of precompensation in the manuals. Has anyone successfully duplicated (and verified) 8" floppies with the SuperCard Pro? Any ideas?

Thanks,
Josh

[admin]

There is a thread here about copying 8" disks, and some people have done so without any problems. However, this can only be done using soft-sectored disks (single index hole). Hard sectored disks can not be duplicated with current software because it expected 1 hole = 1 revolution.

You will have to use the C64 setting with 48 TPI selected.

[joshd]

There is a thread here about copying 8" disks, and some people have done so without any problems.  However, this can only be done using soft-sectored disks (single index hole).  Hard sectored disks can not be duplicated with current software because it expected 1 hole = 1 revolution.

You will have to use the C64 setting with 48 TPI selected.

I've only found two threads:

https://www.cbmstuff.com/forum/showthread.php?tid=211 is related to reading of 8" disks only.

https://www.cbmstuff.com/forum/showthread.php?tid=83 starts off talking about duplicating 8" disks but then diverges into reading 5.25" disks for a Heathkit using a 5.25" 1.2mb drive and never answers the original question, unless I'm missing something.

Is there another thread I'm missing?

The disks in question are soft-sectored and are not in an exotic format (double-density MFM, 256 bytes/trac, 26 sectors / track -- a standard IBM 8" format used by many many computers).  They can be read/written pretty trivially using a standard PC FDC and ImageDisk.

I'm not sure I understand your suggestion for using the C64 / 48TPI setting -- 8" drives have 77 tracks, the C64 only has 38.  I'm not having any trouble reading the disks at all, but writing them back is problematic.  What settings does the C64 setting affect that would improve this?  

I can send some sample disk images your way if that would help.

Thanks,
Josh

[admin]

Yes, send me a sample to: data@cbmstuff.com

Some 8" disks are 40 track, and requires 48 TPI. ALL of the soft sectored disks are index aligned, so as long as you have the proper head step you just need to use INDEX mode just like you do with any PC disks.

Make sure you use the media integrity test to be sure the disks can be written to correctly.

[joshd]

Thanks. Sent an image to you yesterday, let me know if you have any other questions.

[admin]

I sent you an email. Your image looks great. Should be very easy to duplicate. You need to test your disk(s) you are trying to write to with the media integrity test.

[Al Kossow]

There was a discussion on using your board recently on the classiccmp list. I am curious how you deal with write precompensation on mfm data being written. The problem Josh is having sounds like it isn't being performed.
http://www.classiccmp.org/pipermail/ccta...10497.html

[admin]

Write pre-comp is done as part of squishing/stretching the track so that it fits based on the speed of the destination drive. Josh needs to use the media integrity test. Failures in the upper tracks are very common with 3.5" disks. I have never seen it with a 5.25" disk. I don't have a 8" drive for testing, but I am guessing that his disks won't pass the media integrity test. This has been the case with a few others trying to duplicate 8" disks.

If this was a write pre-comp problem you would think that since the 8" disk is a lot larger (data goes by the head faster at the outer edges) that there would be problem more so with inner tracks and not the outer tracks.

After reading through the link above, it seems that some type of special interface is required? I thought that 8" drives used standard 34 pin connectors (the ones I have seen on eBay appear to). What is necessary? What is the TG43 thing? I have been trying to find a reasonably priced 8" floppy drive. Any ideas on what I should actually be looking for? What about the adapter for a 34 pin connector?

[joshd]

I sent you an email.  Your image looks great.  Should be very easy to duplicate.  You need to test your disk(s) you are trying to write to with the media integrity test.

I tested the media with the integrity test; they all fail immediately on the first sector.  This is with several disks across a couple of manufacturers (Maxell and Verbatim).  I am able to use this same media successfully with ImageDisk, with zero errors.

[joshd]

After reading through the link above, it seems that some type of special interface is required?  I thought that 8" drives used standard 34 pin connectors (the ones I have seen on eBay appear to).  What is necessary?  What is the TG43 thing?    I have been trying to find a reasonably priced 8" floppy drive.  Any ideas on what I should actually be looking for?  What about the adapter for a 34 pin connector?

The physical interface is different (50 pin vs. 34 pin for the vast majority of 8" drives).  The TG43 line indicates to the drive to use increased write current for inner tracks (most early 8" drives do not keep track of the track they're on so cannot apply this increased current without outside help).  The DBIT FDADAP board I linked to in my initial post (http://www.dbit.com/fdadap.html) handles this signal and also adapts the standard PC 34-pin interface to the (mostly) standard 50-pin interface.  It's very convenient.

I'd keep my eye out for a Shugart 851, they're reliable and rugged.  If you can find one (or two) already in an enclosure, even better, as that'll solve the power requirements (early 8" drives need 24V DC as well as 115V AC for the spindle motor).