1.44 BM dsk image

Paladin (945)

06-06-2023, 19:19

Disk-Manager (LexLechz.at)
File -> new -> 2 sides, 80 tracks, 18 sectors/track (1.44 MBytes)
Press ok
Save as ...
Give it a name, and it makes a blank disk image.

By Briqunullus

Paladin (750)

07-06-2023, 18:24

gdx wrote:

I wonder if the 720kB limitation is due to the Disk-ROM, the FDD controller or both. If it was just the Disk-Rom, someone probably would done a patch it by now.

Did a bit more testing in openMSX. I patched the diskrom to not support 8 sector tracks anymore and added a new fictitious disk format of 1008K. That's the largest size that still uses a 3 sector FAT. I managed to write 774K of data to it, after which I got a drive error. I'd guess the error originates in openMSX, limiting drive access to 86 tracks.

So yeah, limitations in the diskrom at first (more exactly, the hardware driver). And then there are some limitations in the controller as well. Though on a real machine, the latter could be different. Also unknown if the Gotek can handle this unofficial disk size.

To be continued, I got a few ideas for 1.44MB disks.

By Grauw

Ascended (10818)

07-06-2023, 19:02

MSX-DOS1 can support FAT12 volumes of up to at least 16 MB. The restriction is that you have at most 3 FAT sectors, however you can have larger cluster sizes. Nextor FDISK limits the cluster size of DOS1 compatible volumes to 32 sectors per cluster, I don't know if higher values also work (don't see why up to 128 would not work equally well).

So a 1.44 MB disk should be formatted with a cluster size of 4 to keep the FAT size to 3 sectors and be MSX-DOS1 compatible.

That aside, I always understood that the data rate of high density drives was too high for either the disk controllers used in MSX computers, or for the Z80 to keep up with them, and this would affect a Gotek equally I would think. But I'm far from certain on this.

However even if this may prohibit retrofitting an MSX with a HD drive, I think it should definitely be possible to make a new FDD interface with HD drive support using a more recent type of disk controller.

By mars2000you

Enlighted (6555)

07-06-2023, 19:09

MSX-DOS 2 is probably a better idea for HD, otherwise I don't see why it has been used for the MSX2 Daisen Sangyo MX-2021.

What leads to another question: why what is possible on MSX2 under MSX-DOS 2 has not been included in the MSX turbo R standard?

By st1mpy

Paladin (945)

07-06-2023, 19:20

Was the MX-2021 1.44MB drive or 1.2MB like the PC-9801?

By Briqunullus

Paladin (750)

07-06-2023, 20:05

Just to be clear, the trickery I'm doing is just for fun. And on a let's see how far we get basis. I have a none working version of the diskrom for 1.44MB floppies and it leaves some 18000 bytes free in MSX Basic. That's almost the entire page 3. Of course that will cause compatibility problems on itself!

So don't expect miracles, it may probably only work in openMSX and not on real machines. But I learn a lot about the diskrom and that's the fun part for me.

By mars2000you

Enlighted (6555)

07-06-2023, 20:43

No idea, but both were released at same time in 1988 for professional using.

https://weekly.ascii.jp/elem/000/002/616/2616654/

Interesting precision on ASCII website:

'"A similar system was also developed in the PC-98 series at the time, and MS-DOS was used as the OS there, but MSX-DOS2, which is an OS dedicated to MSX, also has compatibility with MS-DOS."

I don't know to which version of MS-DOS it refers, it can be 3.31, released in November 1987, or version 4.0, released in June 1988, but this MSX-DOS 2 compatibility with MS-DOS also explains the HD support (1.44 support was added in MS-DOS 3.3, released in August 1987).

By Grauw

Ascended (10818)

07-06-2023, 21:12

mars2000you wrote:

MSX-DOS 2 is probably a better idea for HD, otherwise I don't see why it has been used for the MSX2 Daisen Sangyo MX-2021.

Probably because DOS2 supports the standard MS-DOS formatting of 1.44 MB disks with larger FAT.

By sdsnatcher73

Enlighted (4278)

07-06-2023, 23:23

Well the FDD ROM created by konamiman for the RookieDrive NX does support 1.4MB (USB) disk drives, it can format them and it can use them in DOS1. So the Z80 is not a problem with the higher data rate. I do think the disk controllers used in MSXs did not support this high data rate. Do we know which controller was used in the MX-2021?

By cjs

Master (143)

08-06-2023, 06:09

Briqunullus wrote:

I have a [non-]working version of the diskrom for 1.44MB floppies and it leaves some 18000 bytes free in MSX Basic. That's almost the entire page 3. Of course that will cause compatibility problems on itself!

Given that this is all custom stuff anyway, it's reasonable to add some RAM to the disk controller cartridge and use that for buffering. This seems to me likely to Just Work with MSX Disk BASIC (and free up several kilobytes of BASIC RAM), but MSX-DOS may need some tweaks depending on how much it uses the ROM for disk operations and how much it tries to do itself.