77-track "Japanese style" disks

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r09
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77-track "Japanese style" disks

Post by r09 » Sun Nov 28, 2010 9:49 pm

Just wanted to make a small suggestion for DTC: as you probably know, there are several Japanese computers (X68000, PC-98xx, FM Towns...) that use a certain disk format with 77 tracks, 8 sectors/track and 1024 bytes/sector (which I believe was based on the IBM 8" HD format). DTC can dump these disks just fine, but when creating a sector image (-i4 option) it always assumes that the disk has at least 80 tracks and creates an oversized image. You can always manually trim the extra 49152 bytes, but it would be nice to have an option to dump these disks with the correct size easily, if possible.

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mr.vince
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Re: 77-track "Japanese style" disks

Post by mr.vince » Mon Nov 29, 2010 8:41 am

Have you tried -e switch?

r09
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Re: 77-track "Japanese style" disks

Post by r09 » Mon Nov 29, 2010 10:37 pm

Yes, it produces the same image. It seems that DTC always pads the image with 0s to "fill" 80 tracks, no matter how many you actually dump.

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IFW
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Re: 77-track "Japanese style" disks

Post by IFW » Mon Nov 29, 2010 11:09 pm

Yes, that's correct - an image must preserve the default geometry associated with the image type.
There will be an option to enforce track geometry; remove tracks below and above the selected limits - I've put it on my todo list.
e.g. -e77 would still pad the image to an expected minimum number of tracks (40/80 for generic MFM), -ec77 would not include anything above track 77.
[syntax to be decided, but something similar]

r09
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Re: 77-track "Japanese style" disks

Post by r09 » Sun Dec 05, 2010 10:17 am

Thanks. It's good to know it's a planned feature. :)

By the way, I've just dumped the X68000 version of Detana!! TwinBee (the only X68000 game I have) and I'm uploading right now. I really hope it's OK, because the last two tracks of the first disk were in really bad shape and I had to do literally thousands of reads to get a good one. I'm using a TEAC FD-55GFR 149-U5 to dump 5.25" disks, in case you need to know.

Tor
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Re: 77-track "Japanese style" disks

Post by Tor » Tue May 17, 2011 12:14 pm

Sorry for waking up and old thread.. I'm new here.
That 'Japanese' format is interesting - was it used on 5 1/4" floppies?
Because that format (77 tracks, 8 sectors per track, 1024 bytes per sector) is supported by the floppy drive controllers on old Norsk Data minicomputers. Although I believe it would have mostly been used on 8" floppies (later controllers came with two drives, one 8" and one 5 1/4", but I believe that format was supported on the older 8" only controllers from early on). Those controllers could handle a bunch of different formats.
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r09
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Re: 77-track "Japanese style" disks

Post by r09 » Thu May 19, 2011 7:56 pm

As far as I know, it was used on everything. The Sharp X68000, for example, uses the 77-track format on 5.25" disks, while Fujitsu's FM Towns uses the same format on 3.5" disks, and NEC's PC-98 line used both of them throughout its life. It's probably more NEC's "fault" than anyone else, though; they pretty much had a monopoly on the personal computer market in Japan back then, so they set the standards.

mark_k
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Re: 77-track "Japanese style" disks

Post by mark_k » Mon May 30, 2011 6:20 pm

Hi,

Maybe it's not generally known, but many USB floppy drives support the 77-cylinder, 1024 bytes/sector, 8 sectors/track format natively. You can even format a blank 3.5" disk in that format. (See the Linux ufiformat man page.)

While not suitable for SPS preservation purposes, it should be easy to read a plain disk image file from 3.5" disks which use that format, using just a normal 3.5" USB floppy drive and e.g. a tool like dd. For such disks which don't read reliably, you might look into getting a SuperDisk (LS-120) drive. They also support the format, and apparently SuperDisk drives (which have much finer head-positioning resolution than a normal floppy drive) have firmware which finds the "middle" of each recorded track where the signal should be strongest. Or at least the drive adapts/calibrates itself when each DD/HD disk is inserted.

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mr.vince
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77-track "Japanese style" disks

Post by mr.vince » Tue May 31, 2011 2:38 pm

Ok as long as such a disk does not have intentional anomalies (e.g. protection data)... The onboard controller of these USB drives does not hand over raw data.

As for SuperDrives: yes, these could be the ultimate tool, but given the fact that the onboard controller does as well alter the data, it's also unusable out of the box.

r09
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Re: 77-track "Japanese style" disks

Post by r09 » Tue May 31, 2011 8:50 pm

You can also solder some points on the PCB of a Samsung SFD-312B to make it spin at 360 rpm and read the disks correctly, or even better, connect them to a switch and toggle between 300 and 360. That's what I did before I had the KryoFlux, and it worked very well.

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