ICL OPD

[jobdone]

I think Stephen might be the better person to answer, but the OPD format is not a straight DOS format. This is why the images Ideally are formatted with the modified C1OPD rom first. The rom writes a string as a header on the disk where DOS expects to see (it's) header information. By doing this DOS can then read and write to that image (the ST too it seems)but NOT reformat it. I used DOSBOX to play with the images as I know modern machines don't play nicely with 720K's. I also used Hatari (I had to change the file extension from img to st). Now if you already have a image without this header, you could change it with a hex editor (or a better option would be Stephen's tool). How to write them to actual media? I would change the header and possibly try this in DOSBOX as I understand it's a PITA on the OPD although a gotek and an actual floppy is always a good combo. I think another option could be a greaseweazle.

[Chr$]

I've just been experimenting with ImageDisk. With it, I was able to create an image file of my OPD formatted disk containing all the mdv wallet stuff. I was then able to write that image using DOS 6.22 (real hardware) to a fresh 720k disk and that seems to work fine in the OPD, so that's a start - I can duplicate real C1 OPD disks.

But if I format the disk with the OPD and then write an image to it, won't that overwrite everything? I could of course make a blank OPD disk and then write the files to it. I'll try that. I get lost when it comes to headers and such like! How many bytes is the header that I need to pinch from an OPD formatted disk? I saw that program Stephen wrote but I don't have a clue how to use it.

[jobdone]

That's good to know that your image can be written ok. I assume dd would do a similar task? I'm not sure if Stephen updated his header program after he got the rom running? if he did not the header would need to be the same as the one in this pic. From what I understand from what Stephen was saying is that the OPD has it's own format (which is DOS compatible), but the OPD doesn't care/read the header information , however DOS of course does. Stephen also pointed out that because of this if he changed the header to a DOS one, then that is the best of both worlds as far as reading and writing is concerned. He also noted that the Header was just a plain string in ROM which writes to each disk, thus altering this is what is going on with the modified ROM.

[jobdone]

This is just showing what the settings are (hopefully). I copied as many settings as I could from the manual.

[stephen_usher]

Isn't a .IMA file merely a raw image which you can dd or rawwrite onto a 720K floppy?

[Chr$]

Isn't a .IMA file merely a raw image which you can dd or rawwrite onto a 720K floppy?

Yes, but it looks to my untrained eye like the .ima file was not originally a C1 OPD floppy disk. The files contain 'PCML' so they must have been disks made with the other interface. And changing those 2 rows of PCML related bytes to the C1OPD stuff doesn't seem to work. I suppose the structure of the PCML disks is different in some other way.

And thanks Jobdone. What is that 'Disk Image Tool' prog you have running there? I also discovered that SamDisk is capable of dumping a real OPD floppy and then writing it back to another real floppy that the OPD has no issue with. I like SamDisk, have used it in the past for dumping QL software on disk.

[Pr0f]

The other PCML disk interface had a 64180 CPU and ran CPM - so it may be a CPM format or derivative?

[stephen_usher]

Apparently the PCML TeleDrive interface could read C1 disks but would corrupt them if they were written to by it. They are supposed to be PC compatible, i.e. FAT12 with a PC boot sector and with the same geometry as a PC 720K as formatted by MSDOS. The PCML you see is in the DOS manufacturer field of the Boot Parameter Block (BPB).

The C1 disk format is a DOS FAT one but with a slightly different geometry than those generated by default on IBM PCs or the Atari ST. However, the boot sector information (BPB) that's been added in the modified ROM tells the other systems the correct geometry so that they can read and write to them correctly. The C1 interface blindly reads and writes so will screw up if offered a disk formatted on a PC or ST.

[Chr$]

Apparently the PCML TeleDrive interface could read C1 disks but would corrupt them if they were written to by it. They are supposed to be PC compatible, i.e. FAT12 with a PC boot sector and with the same geometry as a PC 720K as formatted by MSDOS. The PCML you see is in the DOS manufacturer field of the Boot Parameter Block (BPB).

The C1 disk format is a DOS FAT one but with a slightly different geometry than those generated by default on IBM PCs or the Atari ST. However, the boot sector information (BPB) that's been added in the modified ROM tells the other systems the correct geometry so that they can read and write to them correctly. The C1 interface blindly reads and writes so will screw up if offered a disk formatted on a PC or ST.

Leaving aside the problem of writing PCML images and reading them on the C1 - I can't read/write from DOS to C1 OPD disks either. XP doesn't like them at all and asks if I want to format them. DOS 6.22 will read the disk but tells me that it's empty and doesn't even show the disk name assigned when formatted.

Just had a play and saved a tiny 24 byte text file using DOS to a pre-formatted blank C1 OPD disk. When I then DOS dir the disk it shows just that tiny file and I was also able to open it but oddly it showed only about 160k free on the disk. I took the same disk downstairs to the OPD and checked it's content - it reports that it contains allegedly 4 different larger random files that were in the same source location as the tiny 24 byte file. The 24 byte file isn't listed and as the copy of it to disk was so fast I don't think the random other files are actually there, it's just the names. Very odd.

[stephen_usher]

I'm not surprised. Microsoft rewrote the filesystem code in MSDOS 6 changing the default format to FAT16, even for floppies.

It sounds like MSDOS 6 must have dropped support for MSDOS 2 FAT12 filesystems (which is what the C1 is writing). It probably requires the extended MSDOS 3 BPB information and possibly even ignores the information in the part of the BPB that the amended ROM installs and blindly uses the "standard" MSDOS format parameters, which is why it would scramble the FAT table and the files.

Windows 98 officially dropped FAT12 support totally which is probably why XP asks if you want to format the disk.

I've not got an MSDOS 3.x machine to test but DOSbox correctly reads and writes to an image as does the Atari ST.