Maybe your 1.44MB floppy drive can't detect Double Density disks : some of the later drives were so cheap that they removed that feature.

As for the XT, this is just a "bug" because all XT bioses can only use 360k 5"1/4 floppy disks. There are several methods to remove that limitation such as using a controller that has a rom, or just through software. DOS 3.3 and up have a function for this, but I can't recall which. Or just use 2M-XBIOS.COM that allows you to do the exact same 😉

When my XT was still working right with floppy disk drives, that's what I did

If it's a newer USB floppy drive, you're out of luck, those don't support 720k. I do have old Teac, NEC and Iomega USB floppy drives and they have no problems with 720k, but new noname drives (like ConnectIT) simply won't do.

Not a USB floppy drive -- I forgot the brand but it came with the old Dell XPS. It is strange that it can't format the disk anything while taped, but if I format the taped disk in the XT (which is actually a Tandy 1000 running DOS 5) then the Dell will recognize that now 360K formatted disk..

Are you saying that any XT machines could only use 360K disks -- even if they had 3.5" floppy drives?

Deksor wrote:

As for the XT, this is just a "bug" because all XT bioses can only use 360k 5"1/4 floppy disks.

Sorry, that's not correct.

I haven't tried formatting 720k floppies for a long time, but I remember that just taping the hole didn't work for me. Maybe there is something else than just a hole?

On the other hand, when mice still came with drivers on a floppy, those floppies were often real 720k ones, even when 1440k were already standard.

Why do you even need to tape over the hole except for auto detection purposes?

I can still format to 720k with Windows 10 and a 2x speed USB floppy or a floppy from a Dell laptop that has a USB plug so you can use it externally while still having the CD-ROM drive installed.

I just have to use the command prompt because the Windows GUI for some reason fails every time, just saying that it is a bad disk.

What OS are you running that is having the problems formatting to 720k? It could also just be a faulty floppy drive.

Back in the day, I used to do the opposite and use a hole punch to make 720k disks into 1.44MB disks.

If you cover the hd detection hole, the disk drive will use a lower write current, since that is different between dd and hd. However, that lower write current is too weak for the coating of hd disks. It's not supposed to work.

I tried to format floppies that I thought were HD diskettes (1.44MB), and my computers wouldn't format the diskettes whatsoever, and I learnt the hard way, found out later that the diskettes were DD (720KB) diskettes. Used the command format A: /F:720 to format all of the diskettes, and as luck would have it, I got it to work. This was on a 1.44MB/1.2MB 3.5" 5.25" dual FDD.

konc wrote:

Deksor wrote:

As for the XT, this is just a "bug" because all XT bioses can only use 360k 5"1/4 floppy disks.

Sorry, that's not correct.

Okay maybe not ALL of them, but like 90/95% of them. That's exactly what my XT did : it reported my 1.44 MB 3?5" drive as a 360KB 5"1/4 drive with si.exe

Deksor wrote:

konc wrote:

Deksor wrote:

As for the XT, this is just a "bug" because all XT bioses can only use 360k 5"1/4 floppy disks.

Sorry, that's not correct.

Okay maybe not ALL of them, but like 90/95% of them. That's exactly what my XT did : it reported my 1.44 MB 3?5" drive as a 360KB 5"1/4 drive with si.exe

Yeah still no. Please don't come up with numbers like that, I really don't want this to sound personal or anything but it's just plain wrong. Yes there are early XTs understanding only 5 1/4 360KB floppies, even OP's might be one of those, but the numbers are closer to the exact opposite of what you wrote.

Many XT BIOSes also supported 720k drives (including later revisions of the IBM PC XT).

Isn't the 360/720 thing mostly a DOS version issue??? I stuck a 720 in an IBM XT no problems back in the day, was using DR DOS 6 at the time. I thought it was MS DOS 3 or below that couldn't even 720.

Ok, so I tried a different brand of floppy -- this time a 1.44M from 3M and was able to format it to 720K on the Dell DOS 7.1 system when taped.

This confuses me...

Tandy SX (MS DOS 5.0) -- Can read 720K disks that I've formatted on the Dell, but whether taped or untaped /F:720 always yields "Parameters not compatible". Format without any parameters will format any floppy to 360K - tape or no tape.

Dell XPS (MS DOS 7.1) -- Can read 360K disks formatted on Tandy, but will give "Parameters not compatible." if you try to use the /F:360 command on it.

They can both read 360K and 720K but each can only format a disk to one size? I don't get it.

I don't know if this is a useful piece of information, but I got an XT clone with both 360KB (5.25") and 720KB (3.5") drives installed.
Originally, I thought the 3.5" drive it came with was an early 360KB model,
since without loading any additional floppy driver, both drives were stuck to 360KB of capacity.

Luckily, I was wrong. It was a double sided DD drive at least and worked jut fine after loading 2M-XBIOS.
But since the BIOS is very old (probably dated ~84) and unique, I have no idea what caused this 360KB limit.
Maybe a DIP switch was incorrectly set by the previous owner ? I don't know.
Again, I don't know if this is useful information. A Tandy isn't behaving exactly like an IBM PC/XT.

konc wrote:

Deksor wrote:

konc wrote:

Sorry, that's not correct.

Okay maybe not ALL of them, but like 90/95% of them. That's exactly what my XT did : it reported my 1.44 MB 3?5" drive as a 360KB 5"1/4 drive with si.exe

Yeah still no. Please don't come up with numbers like that, I really don't want this to sound personal or anything but it's just plain wrong. Yes there are early XTs understanding only 5 1/4 360KB floppies, even OP's might be one of those, but the numbers are closer to the exact opposite of what you wrote.

If you say so ... But I've got 3 XT boards (2 IBM from 1986 and a more modern one from 1988) and none of them do support 3.5" floppy disk drive. A friend of mine also have an XT with the same problem and I've seen many like that on the internet

Anyways ...

I have the manuals -- so I'll check for a DIP switch. I just think it's strange how it can read 720Ks but not format them... and likewise how the Dell's drive can read 360K 3.5s but not format them.

That's exactly what my XT from 1988 did ^^

2m should be able to fix this (if your controller supports 3.5" drives of course, but I think it should be okay. If not, that'll just not work)

No DIP switches -- the manual makes no mention of adding a 3.5" drive - the SX originally came with two 5.25".

What exactly is this 2M-XBIOS.COM ? Is it just a program, does it actually flash hardware or... ? Is it an unnecessary solution anyway since you said

DOS 3.3 and up have a function for this

and this machine is running DOS 5.0.

infiniteclouds wrote:

Ok, so I tried a different brand of floppy -- this time a 1.44M from 3M and was able to format it to 720K on the Dell DOS 7.1 system when taped.

This confuses me...

To quote myself:

If you cover the hd detection hole, the disk drive will use a lower write current, since that is different between dd and hd. However, that lower write current is too weak for the coating of hd disks. It's not supposed to work.

It's pure luck whether it works or not. And data written to such formatted disks is completely unreliable.