Why MSX-DOS can't read 800kb disks? Is a hardware (floppy drive, FDC) or a software limitation?

I think you mean the 800KB format that Apple used. This required a special hardware that rotated the disk slower when reading/writing outer tracks, so this is hardware limitation. Different MSX-models have different disk controllers, so the actual hardware limitations vary a bit from model to another.

How ever MSX-DOS can read/write 738KB disks as long as disk drive hardware supports it. (Just big enough to fit .DSK file to it ) I've tested this successfully with Panasonic MSX2+, tR and Phillips 8250. Sony HB-P900 original drive made just really bad sounds. Problem is that Windows PC can't read those disks. I don't know about Linux.

I remember using either 83 or 85 tracks instead of a standard 80 (each track contains 9K). I don't remember whether I used BIOS, BDOS or anything else to access those extra tracks. I used them in my copy protection code (nobody around me knew about that, so it was pretty good protection then).

IIRC 800K means extra sectors on each track. They can be read on PC using special software.

But the real problem is formatting those extra tracks and/or sectors. I think you will need a special tool for that. But wait ... the extra tracks and sectors can be specified in MS-DOS/Windows format command, right ?

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I remember using either 83 or 85 tracks instead of a standard 80

Yes, that's the trick... I would not go over 82 as even this causes problems on some disk drives. (eg Sony)

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But wait ... the extra tracks and sectors can be specified in MS-DOS/Windows format command, right ?

ROFL cax, you are hilarious! (I still hope that my WinXP could format even standard 720KB disks)

uhm.. XP can even format 5.4" disks, so where's the problem in that?
(alas no 800KB floppies though)

I don't know about 5.4" disks, but normal 720KB DD disk formating does not work. Fortunately normal read/write still works.

Unfortunately Microsoft operating systems on PC have not ever used the Microsoft standard while handling disks. For example reading/writing 360KB MSX disks do not work correctly on any version of Windows, but fortunately support is better for example on Mac and Amiga.

On PC you can format your disks with several formats. 160, 180, 320, 720, 1.2MB, 1.44MB, 2.88MB. Those formats (except the latter one which requires a ED drive (think it was called that, Extra Density or something)) should be able to be read without extra software, atleast on PC. You can also format with 820, 1.72MB, 1.68MB formats, which might not be compatible with all systems. Then there is the DMF format, which MS used to distribute their software, ie. Windows 95 for example. The first disk was just a normal 1.44MB disk, including a sort of driver to read the bigger DMF disks.

Try winimage, a freeware / shareware tool, it lets you format your disks in a lot of formats. You can then just try them on your MSX

Hey, that WinImage was a great tip, it worked! It seems that in WinXP the formating of 720KB disks is disabled only from FORMAT.COM and GUI (?)

Hmm... I'm just wondering what would happen if I would copy FORMAT.COM from Win2000 for example...

Can WinIMage format single sided double density disks that work on such diskdrives on MSX? And also read them out and extract the files written by the MSX?

I tried calling format from command line, but it failed:

format a: /T:80 /N:9

Here is what MS says about that: http://support.microsoft.com/kb/302113

In short, either earlier Windows/DOS should be used, or special tool is required for formatting.

NYYRIKKI: format.com from Win2000 or even WinNT won't help you - you need Win9x or plain DOS for that.

FORMAT works fine in Windows XP, only the GUI lacks support.

Using the command that cax has posted, a 720KB floppy could be created without problems; you only need to cover the HD hole to fool the drive (or use a real 720KB floppy).

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uhm.. XP can even format 5.4" disks, so where's the problem in that?

The problem lies in the fact that 5.4" disks don't exist. Try 5.25"

5 1/4, 5.25, go figure

Indeed - the problem was the HD hole, jltursan is right. Format works on XP.

So, that MS Knowledgebase article is just wrong? MS doesn't know the capabilities of its own software?