DaveDDS wrote on 2025-02-12, 22:48:

There is an interface difference between 720k and 1.44m 3.5" floppy drives. The 720k transfers data between drive and controller […]
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There is an interface difference between 720k and 1.44m 3.5" floppy drives.
The 720k transfers data between drive and controller at 250kbds ... the 1.44
transfers at 500kbps. This is how it stores twice a much data - twice as many
bits are written to each track (by sending them twice as fast).

So, for 1.44 you not only need a drive and media that can handle the faster
rate, you also need a controller in the PC which can be switched to 500kbps ....
is it possible this system does not have an FDC that supports that rate?

-- This is why the original PC/XT couldn't support HD (1.2m) drives, they
(with a improved FDC) came out in the AT. Being a 286 .. this is probably from
a similar time period, and nobody knew what standards to follow, because the
standards either didn't exist yet, or were so new that they had not been
widely adopted.

You're right about this. I think a workaround for this was to either use a 16-Bit ISA multi-i/o card or an floppy interface based streamer card (for backup tape drives).
Since only the 8-Bit portion was used by FDC on multi-i/o card, it was possible to use the card for this purppse.
On software side, DOS' built-in solutions like driver.sys or driveparm could be used to make an 1,44 MB drive available to DOS environment.
Or even better, 2M-XBIOS, a third-party floppy BIOS. https://forum.vcfed.org/index.php?threads/2m- … or-pc-xts.9672/

Jo22 wrote on 2025-02-13, 19:11:

You're right about this. I think a workaround for this was to either use a 16-Bit ISA multi-i/o card or an floppy interface base […]
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You're right about this. I think a workaround for this was to either use a 16-Bit ISA multi-i/o card or an floppy interface based streamer card (for backup tape drives).
Since only the 8-Bit portion was used by FDC on multi-i/o card, it was possible to use the card for this purppse.
On software side, DOS' built-in solutions like driver.sys or driveparm could be used to make an 1,44 MB drive available to DOS environment.
Or even better, 2M-XBIOS, a third-party floppy BIOS. https://forum.vcfed.org/index.php?threads/2m- … or-pc-xts.9672/

I use 1.44mb drives in DOS (I tend to use 5.0, but I know 3.3, 4.0 and PCDOS 7.1 all work as well) all the time without
having to load any special drivers (I often boot fairly minimal floppy based setups)..

For DOS to work with a 1.44m drive, you need hardware (FDC that can do 500kbps), and software that knows
how and when to switch - I think this normally happens through a negotiation with BIOS (perhaps DRIVER.SYS can
work around needing this?)

If your mainboard FDC can't do 500kpbs, you might be able to use an add-in card that can, but you'll have to
disable the on-board one... Hopefully the add-in card will offer a BIOS extension to support it, or have
appropriate drivers to enable it's extra capabilities.

-- Sorry I can't be more specific on what needs to happen with DOS/BIOS... I've not had/used a system which
doesn't support HD drives in a very long time... I do have a LOT of experience with drives and the FDC, but that's
almost all from my software (ImageDisk) which completely bypasses DOS&BIOS and talks directly to the FDC
hardware in order to do things that it (hardware) can accommodate, but DOS&BIOS haven't got a clue about...

Dave ::: https://dunfield.themindfactory.com ::: "Daves Old Computers"->Personal

DaveDDS wrote on 2025-02-13, 21:44:

I use 1.44mb drives in DOS (I tend to use 5.0, but I know 3.3, 4.0 and PCDOS 7.1 all work as well) all the time without having t […]
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I use 1.44mb drives in DOS (I tend to use 5.0, but I know 3.3, 4.0 and PCDOS 7.1 all work as well) all the time without
having to load any special drivers (I often boot fairly minimal floppy based setups)..

For DOS to work with a 1.44m drive, you need hardware (FDC that can do 500kbps), and software that knows
how and when to switch - I think this normally happens through a negotiation with BIOS (perhaps DRIVER.SYS can
work around needing this?)

If your mainboard FDC can't do 500kpbs, you might be able to use an add-in card that can, but you'll have to
disable the on-board one... Hopefully the add-in card will offer a BIOS extension to support it, or have
appropriate drivers to enable it's extra capabilities.

Hi, thank you for reply! I think same.
The oldest DOS I do use for 1,44MB floppy support is PC-DOS 3.30, btw! 😁

On my XT, which as 250 kbds floppy controller, I'm using 2M-XBIOS to add 720KB floppy drive support for drive B: at the BIOS level (it's a Gotek).

That's because the BIOS on that PC is from 1984/1985 and isn't aware of "720KB drives" yet (I know, it's more about numbers of tracks, sectors etc).
There are no jumper settings on the mainboard, either.

That's why it came to mind in first place. 😅
Using 2M-ABIOS might solve same problem of OP with 1,44 MB type on an old AT class system, provided that the floppy controller is able to do 500 kbit/s.

I haven't tried, though. It's just an idea.