senrew wrote on 2024-07-10, 14:29:

I feel kinda dumb asking this but I haven't been able to find an exact answer.

I have an XT, 1986 version. Latest BIOS. It has the stock floppy controller. I can't find any DD 3.5" drives so I was thinking of plugging in a HD one from my pile. Will the controller see the drive and just use is as a 720k drive or will it not work at all?

I don't think it will work.

When you use an HD drive to write DD diskettes, the controller tells the head to "double-step", that's because the track head (and track width) on an HD drive is narrower, so it writes the wider track "twice" so-to-speak to be able to accomplish this.

If the computer is unaware of this, then it won't work.

Most probably it'll work. Not all drives and not on all controllers, but generally you can just replace it with an HD. Of course you'll need to use DD disks (or HD with the hole covered), because the controller won't know anything about HD but the drive will.

Was thinking of something like this. The spec sheet calls it Dual Density and lists 300/360 rpm. Dunno if that's something special or just marketing for something all 1.44 drives can do.

https://www.ebay.com/itm/156243900059

senrew wrote on 2024-07-10, 14:29:

Will the controller see the drive and just use is as a 720k drive or will it not work at all?

Might be neither. It will work, but not as-is. Depending on the drive in question and controller/BIOS you might need a mod or two. That would also depend on what media you have and intend to use. If you have DD floppies, it might just work as-is. For HD floppies you'd most likely need to cover the hole or bypass the media type sensor.

Double-stepping only applies to 5.25" drives, where DD ones use 40 tracks and everything else uses 80 tracks. Not an issue for 3.5" drives. Media type is an issue but since the magnetic properties of DD and HD 3.5" floppies are quite similar you most likely will get away with just covering the hole or sensor bypass even when using HD floppies in DD mode. This might be more of an issue with a real DD drive, but you are planning on using HD one. Lastly the 300/360 rpms only applies to 5.25" drives and JP 3.5" floppy formats. I assume you'll be sticking to pure DOS so you don't need, or even want a drive with switchable speeds as this will only require more modding to prevent it from happening (although there is usually a jumper to enable/disable that).

Yeah, the goal is just to use 720k disks on the XT. Just can't find a 720k drive to just stick in the thing.

I'm using a Gotek floppy emulator in an XT (on-board FDC).
It supports reading/writing 360KB and 720KB images.
To add full 720KB support I had to load a floppy BIOS, though.

https://minuszerodegrees.net/2M-XBIOS/2M-XBIO … 2M%20as%20B.htm

Another alternative was to load driver.sys or use driveparm.
The floppy BIOS seemed like a better solution to me, though, considering the age of the PC's BIOS.

I didn't add a 16-Bit floppy controller to make it work.
For 720KB, the XT era controller is good enough.

As mentioned.. 5.25" and 3.5" are different. The RPM/double-stepping stuff is 5.25" drive specifc.
3.5" drives will just write narrower sectors on 1.44MB disks. The speed needed to write such sectors exceeds the XT controller's abilities.
I suggest you just grab a 1.44MB 3.5" drive and plug it into the XT's controller. Nothing bad will happen.. at worst it will not recognize your disks. Of course, stick to 720K disks, or cover the whole for 1.44MB disks to fool the drive into thinking they're 720K disks.
My TurboXT came with a 720KB 3.5" drive, but I've removed it in lieu of two 360K 5.25" drives as is typical of XT machines. Almost all XT software shipped on 5.25" 360K disks anyways.

Almost all XT software shipped on 5.25" 360K disks anyways

Except laptops. I had owned an Toshiba laptop that was an 8088 system.
It had two 3,5" DD floppy drives, with 720KB I think. Because, I could boot original from PC-DOS 3.30 disk.

I have DOS 5.0 and WP 5.1 on the machine. XT-IDE for a hard drive. I pretty much just use the thing as a distraction free writing machine. I was thinking of putting in the higher capacity floppy to make document transfer easier. I did find this. Any experience with it?

https://github.com/skiselev/isa-fdc

When I got back into retro I tried and failed getting many different floppy drives and disks to work. But in then end just got a gotek and never looked back. Gotek with oled and encoder is the way to do this in 2024. The disks and drives are just too old. Can you make it work? Yeah probably if you are determined. But we have a better way now.

I keep buying more and more goteks for all of my builds 🤣.

I like using those usb sticks that look like Bluetooth transmitters

Yeah, that was another thought I had. It just...makes the XT kinda ugly is all 😀

senrew wrote on 2024-07-10, 16:56:

I did find this. Any experience with it?

https://github.com/skiselev/isa-fdc

I think this is not any different than any other standard ISA FDC. I doubt it would enable an XT to consume 1.2MB/1.44MB disks.

Yes, you can use a hd 1440k drive in the place of a dd 720k drive. It will work perfectly fine. Of course it will only work as a 720k drive without BIOS and faster floppy controller.

I did this a long time ago to install Windows 3.0 on an IBM XT.