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Single-sided 250kb 3.5" Floppy Drives.

Chr$

Chr$

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This may not belong here as I don't think IBM compatibles ever supported them - too early (or simply not considered), even for the original PC? But I hope to clear up the origin.

I have encountered 2x single-head, what appear to be 67.5TPI 250kb floppy drives. The earliest (show below) is a Chinon F-351 with chip dates from 1983 (latest) and the other is a Panasonic JU-312 with a label entirely in Japanese and chip dates 1984 (latest).

Fascinating, really odd just seeing one lower head in them. The size is non standard too, compared to 'normal' 720k and 1.44mb drives.

But in which systems were these types of drives used? Were they ever used or were they superseded before they were even mounted in any kind of computer?! And is there any way I can test one using an XT or a choice of later IBM compatibles.

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Apple shipped the original couple Macintoshes with single-sided 400k drives. Is this something similar but with different formatting leading to the different capacity? I know at least that PC double-density disks were 720k and Mac could format them to 800k.
 
3lectr1c said:
Apple shipped the original couple Macintoshes with single-sided 400k drives. Is this something similar but with different formatting leading to the different capacity? I know at least that PC double-density disks were 720k and Mac could format them to 800k.
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Disclaimer on the 250kb capacity: that's just what I found from googling and assumed to be correct as I think one source was a manufacturer manual. Perhaps it's 250kb formatted and 400+ unformatted and maybe they're the same.
 
67.5 tpi means 40 tracks. 40 track 3.5" drives showed up mostly in industrial equipment including sewing machines and serial port connected drives like the Tandy PDD. Looking at Disk Trends from 1984, a lot of Japanese companies were making them including Alps, Teac, Canon, and YE-Data. There may be other more obscure short lived products using them matching the flood of 3" external drives that were available for 8-bit machines in Europe and Japan.
 
krebizfan said:
67.5 tpi means 40 tracks. 40 track 3.5" drives showed up mostly in industrial equipment including sewing machines and serial port connected drives like the Tandy PDD. Looking at Disk Trends from 1984, a lot of Japanese companies were making them including Alps, Teac, Canon, and YE-Data. There may be other more obscure short lived products using them matching the flood of 3" external drives that were available for 8-bit machines in Europe and Japan.
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The single sided head inside certainly reminded me of the single sided 3" drive within a ZX Spectrum +3.
 
Timo W. said:
Looks similar to the drives used in the IBM PC JX:
en.wikipedia.org

IBM JX - Wikipedia

en.wikipedia.org en.wikipedia.org
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Except the JX had double sided 80 track drives (the common 720K) but only used half the disk before a BIOS update.

Note that TEAC's FD-35A (single sided 40 track) was $93 while the single sided 80-track FD-35E was $95. Double sided drives were $104 (40 track) and $122 (80 track). There wasn't much reason to stick with the 40 track drives unless the system could not accept 80 tracks.
 
Chr$ said:
And is there any way I can test one using an XT or a choice of later IBM compatibles.
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At a glance, that looks like a Shugart interface. If so, set the drive select jumper to the second drive position, and it seems like it would function. On an AT, BIOS might need to be set to 360k instead of 720k depending on how it uses the Disk Change/Ready line.

To format a disk, you might need to use a formatter that lets you specify the geometry. Although, at single sided 40 tracks, DOS might recognize it as a "180k" 5.25" drive.

It would indeed be interesting to know what system this came from.
 
krebizfan said:
Except the JX had double sided 80 track drives (the common 720K) but only used half the disk before a BIOS update.
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Maybe the very first models had not? Even the first Atari ST in 1985 used single-sided drives in the beginning. It's not that 720k double-sided drives just poped up out of nowhere. There was development happening and the first 3.5" drives were single-sided.

Not that it matters. Like I wrote, they look very similar in color and design. Did not say they are the drives used in the JX. Information on the JX is very sparse anyway.
 
Here's the other one, the Panasonic JU-312 with spindle motor dated 14 March 1984 and attractive aluminium door. It's dimensions are the same as the Chinon above and also the mounting screw holes are in the same places.

I'll get them cleaned up, lubed and will attempt to format a disk with them set as a 360k 5.25". Both have quite clear DS jumpers numbered 1 - 4 (so 1 is DS0 and 2 is DS1). I suppose it will be beneficial to wipe a magnet over any 720k test disks first, or their pre-formatted tracks may interfere with the new ones laid down by these old drives.

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Just found the origin for the 2nd drive (above) with the metal door. It was provided with the Opus Discovery 1 Disk drive interface for the ZX Spectrum and in an original ad is was specified as a 250k drive (formatted I assume).
 
I can confirm that setting one as a 360k 5.25" drive in the BIOS and then formatting just one side with the /1 switch resulted in a 180k single sided disk. The Panasonic worked, the Chinon unfortunately didn't - the head assy doesn't move at all, not even initial seek and it's free on its rails. Feels odd though compared to the other one in that it's smoother to move and not so 'steppy'.
 
Crank up IMD and see if you can seek out to track 79. One can format an 80 track, single-sided drive with 40 tracks, leaving the remaining tracks unused.
 
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