External 5.25" USB Floppy Drive, Experiment #1: Boot disk 💾
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- Опубліковано 8 вер 2024
- This is an experiment in getting a 5.25" floppy disk drive to work via USB, connected as an external device. My first test (as shown) is to get a laptop to boot: I'm very happy to say it works!
I did not discover this technique; I am standing on the shoulders of giants. This experiment is based on pioneering discovery work by @dospedition4207 in 2021. He found that the USB "controller card" from an early-era NEC model UF0001 3.5" disk drive, combined with a 26-to-34-pin cable adapter, can be used to connect a 5.25" disk drive and successfully boot a PC into DOS using a Windows 98 boot disk under the right conditions.
His excellent video is here, and was the basis for my work. I ended up using a similar, though not identical controller.
• How to build a working...
Booting via USB depends on BIOS and related feature support, and so this approach may not work on all computers. That being said, I was able to boot a Fujitsu laptop and a Pentium 4-based desktop computer via this method.
As @dospedition4207 demonstrated in his video, disk I/O appears to work OK when booting from the 5.25" disk via USB and from the command prompt. I get the feeling there will be some flakiness and instability, but I have not done extensive testing.
I have done a lot of research in getting to the demo I have today, and I am planning a longer video going into various drives and techniques I have looked into. The set-up featured here, thus far, has been the most successful.
HARDWARE NOTES: I used an external power supply because my 2006-era laptop battery is dead, and the original power cable is faulty. The 110VAC "Jackery" power supply was thrown in for fun, illustrating why 5.25" drives aren't very external and portable-friendly. The 110V source here drives a "power brick" / adapter, which outputs 5V and 12V for the floppy drive.
GENERAL DISCLAIMER: all of this is very experimental. Do not try this using hardware you depend on, or with floppy disks containing precious memories etc.
From the demo, @dospedition4207 also showed that his drive had I/O trouble or did not work at all from within Windows. I found similar on my laptop with Windows XP, and I have some theories about ways to get it working. "Stay tuned."
3.5" floppy drives are widely available as USB devices, but it seems that 5.25" drives were just left behind. USB was introduced when Windows 95 was the dominant OS, and CD-ROMs and 3.5" floppy disks were everywhere.
Searching online, I found inconclusive results and no real definitive answers for "5.25 USB floppy" and similar. Despite this, it seems to be a topic of interest among archivists and hobbyists alike, with a Google Groups thread as far back as 2007 saying, basically, "5.25 USB Floppy!? Just kidding, but wouldn't that be great!"
I am hoping to discover and contribute further to this topic, because it would make a lot of people happy - including myself. 😉
Signals are more than "Similar enough", they are the same.
Agreed, they’re identical across all drives attached to the cable (outside of the drive select, whatever pins are on the twist.) Any pointers appreciated! My comment about similarity was about how the host controller and computer sees this 5.25” drive, vs. a 3.5” on this set-up. In Windows, the 5.25” drive spins and stops a number of times in Explorer before showing the “format prompt” modal. I have found one way to make it work, stay tuned… 😆
@@scottschiller "spins and stops a number of times" could just be a function of the drive, but I would try changing some jumper settings if the drive has jumpers. Back in the Amiga days (the drives acted different to PC drives) we were able to tweak PC drives (sometimes cutting and rerouting tracks) to work as 880K 5.25" drives fully compatible with the Amiga 3.5 drives. Teac drives were really good due to the excessive amount of jumper configuration. As far as the PC is concerned, the signals are the same though you might look a head loading (high vs low density) and 40/80 step jumpers to set the proper capacity you need.
Thanks for the note. I saw a few posts about re-wiring PCB layouts in my research, indeed! Wild stuff.
I just got a Teac FD-55GFR, and there is some documentation about a jumper to force it into 300 RPM if needed.
The drive in my video is an Epson SD-680 and I was able to find the jumper details online, and enable "dual-speed" (300/360 vs. only 360?) mode. I had assumed 300 would be the default, but apparently not per this note; I must be missing something, here. ftp.epson.com/desktop/SMD680.TXT
It's interesting hearing and seeing the drive switch when reading an unformatted disk, and when I tried formatting at 720K using `fdformat` on DOS. Per Wikipedia, "List of floppy disk formats," it appears most IBM PC-DOS 5.25" formats use 300 RPM - but, NEC PC98 (Japan) runs most 5.25" formats at 360 RPM - and testing with a basic tachometer, it seems the spindle underneath my drive is rotating at 360 RPM most of the time. I just got the Teac drive, and haven't tried measuring yet - but it sounds similar to the Epson. I'm not exactly sure how the drive / controller determines the speed on 5.25" - is it a combination of reading the media byte, and/or disk layout?
@@scottschiller For a PC you use 300 RPM for 360Kb 40 track double density disks, and 360 RPM for 1.2Mb 80 track high density drives. You can use an unofficial 720Kb mode by configure a 80 track drive to low density by retaining to 80 tracks, which doubles the capacity and is the same format used for 720Kb 3.5 inch floppy disks. With some tweaking you can get 900Kb+ out of a 360Kb disk when used in an 80 track drive. If I recall (for a drive set to 1.2Mb in the BIOS), the BIOS will set the drive to HD 360RPM 80 track mode first and try to read, and then if reading fails it will try DD 300RPM 40 track mode. As for NEC PC98, well, its a very different beast.
Great info, thanks. I have been trying to format 720KB on a 5.25" with mixed results, but I think that's a good place to dig given it applies to both 3.5" and 5.25" types.
I thought 5.25" @ 1.2 MB could work if the controller sees it as a NEC PC98-type 1.2 / 1.23-MB format, but no dice yet. I've been able to format, but seemingly not write a PC98-based 3.5" disk image successfully to 5.25" yet. It may be the imaging tool I'm using, complaining because it thinks 5.25" doesn't (or shouldn't) have space for the 1.23 MB format. Fair enough, under normal circumstances. ;)
Thus far, I haven't been able to get this USB controller / drive combo to read a 5.25" formatted as anything other than 1.44 MB, at present.