Mitsumi patents relating to Quick Disk (FDS)

[mark_k]

Hi,

I searched for patents assigned to Mitsumi that might be relevant to the Disk System.

The most interesting/useful is a Japanese patent, JP 63004477 (A) dated 1988-01-09. The English title for that is "File management system for magnetic disk", and there are diagrams showing the header, directory, gap, id, sector data, sync, crc etc., which could be similar to the FDS disk layout. Maybe someone who can read Japanese would like to take a look? There could be some useful info there.

US patent 4665453, filed on 1984-04-25: "Floppy disc recording and/or reproducing apparatus" appears to cover an alternative top-loading drive mechanism which wasn't used for the FDS. This page has a picture of a drive with that type of mechanism.

US patent 4573572 "Recording disc cartridge" covers construction of the disk, not particularly useful, as is D287597 "Magnetic disc cassette" covering the external design.

US patent 4669009, filed on 1983-10-25: "FLOPPY DISC RECORDING AND/OR REPRODUCING APPARATUS HAVING A LOADING MECHANISM FOR LOADING A CARTRIDGE WHICH ACCOMODATES A FLOPPY DISC" actually seems to be a 3" floppy drive, so not relevant here.

[rbudrick]

That top loading one was used for the MSX, as I have one. No clue how to use it, though. My MSX skills are almost nil. I heard the MSX, MZ-1500, possibly Amstrad and maybe others could copy FDS disks, but I have no clue how. I even saw a pic of an FDS drive somehow hooked to a MZ-1500, but no pic of the connection itself.

Whoa, that link to the top loader mentions it was used for the TI CC-40. Interesting. That's news to me. Never heard of that machine. I wonder what good that machine was even for. I have to wonder if that top loader was an add-on (like a second drive) or if they just mean that area in the top right of the CC-40 image was the QD drive and used the same technology as the top loader.

I can't make out what that supposed disk area reads as in the second pic other than CAUTION static electricity blah blah blah. Hmmm.

-Rob

[segaloco]

Necrobump but is anyone aware of a current copy of the referenced Japanese filesystem patent anywhere? This link is dead.

[Fiskbit]

It took a bit of searching, but I believe this is the patent. It seems we don't have this one on our patents page.

[TakuikaNinja]

Interesting. I've flicked through the Japanese patent and the invention seems to be regarding a filesystem format on the Quick Disk (spiral type disk) that addresses the limitation of only being able to modify the final file on a given disk side. Quoting sections from the translated version (seems to be accurate enough):

Problems to be Solved by the Invention:
The conventional spiral type disk device can delete the last file among a plurality of files recorded on a spiral track by subtracting the number of recorded data files in a directory, Further additions can be made. However, there is a problem that a file recorded before the last file cannot be deleted or changed to increase the data size.

Means for Solving the Problems:
In the present invention, the spiral track corresponds to a plurality of sector portions each recording a part or all of a single file with a predetermined recording capacity, and a plurality of sector portions corresponding to each. And a directory section for recording heading information to be recorded. Thereafter, when a file is recorded in each of the plurality of sector portions, at least a file name of the file and heading information including the presence / absence of recording are recorded at a position corresponding to the sector portion where the file in the directory portion is recorded. Further, at the time of recording and reproduction of the file, the position on the spiral track of each of the sector part where the file is to be recorded and the sector part where the file to be reproduced is recorded is found with reference to the directory part. In the present invention, a plurality of sector portions are set in advance on a spiral track, and a file is recorded in sector units. Therefore, even when the data size of the file increases due to the change, additional recording can be performed in another sector. Further, the presence / absence of recording of each sector part, the recording file name, and the like are recorded in the director part. For this reason, an arbitrary file can be deleted by rewriting the presence / absence of recording in the director section to nothing.

It basically creates a directory + sector abstraction on top of the spiral track to allow for "arbitrary" file access/modification. The Triton Quick Disk Drive and similar QD drives for home computers could have benefited from this. Was it ever implemented in a commercial product?

[segaloco]

My knowledge of QD devices is limited to word processors and music equipment (and FDS) but I haven't done much research into conventional home computer use beyond yep it's a drive and people used it.

[Pokun]

I'm reading it over and over again but it's very hard to understand what it's trying to say.
Does it mean that the data of the files are spread out in sectors that are separate from the file's header and kept track of using a directory in the header that refers to the location of each sector that belongs to the file?
So that you can basically add a new sector anywhere on the disk as long as you update the directory with its location and the file size field in the header. And if deleting a sector that space can be used to add a sector for another file as long as updating both directories accordingly.

If that is the case I don't think the FDS BIOS can use such a system as a file's data comes directly after the file's header. But of course one could use the BIOS' filesystem for the initial files loaded at boot then use a custom filesystem for all other files.

[segaloco]

Well and my question there would be do dumps actually represent a strict linear matrix of the disk contents or some sort of logical structure? I would assume it matches but there is always the mechanism for reading the disk obscures the actual physical ordering of individual data samples on the surface. I'm sure this is well known I just don't know the details myself.

[TakuikaNinja]

I'm reading it over and over again but it's very hard to understand what it's trying to say.
Does it mean that the data of the files are spread out in sectors that are separate from the file's header and kept track of using a directory in the header that refers to the location of each sector that belongs to the file?
So that you can basically add a new sector anywhere on the disk as long as you update the directory with its location and the file size field in the header. And if deleting a sector that space can be used to add a sector for another file as long as updating both directories accordingly.

That sounds about right. The file metadata is stored in a directory block after the header, and each sector has their own header block containing the sector number (labelled as "ID" in the diagrams). The patent mentions that the amount/size of the sectors are fixed (1KiB data per sector is presented). Diagram 5 (bottom of page 7) shows the logical disk structure. A & B denote logical files occupying one or more sectors, while C denotes empty sectors. It resembles the FAT format used on traditional floppy disks.

If that is the case I don't think the FDS BIOS can use such a system as a file's data comes directly after the file's header. But of course one could use the BIOS' filesystem for the initial files loaded at boot then use a custom filesystem for all other files.

That is correct. I doubt Nintendo would have permitted such a flexible structure for the QD even if it was invented before the FDS. Piracy & bootlegging was bad enough with the existing format...

[Oziphantom]

turns out there was a QuickDisk for the C64, "Triton Quick Disk Drive" and it has a very complete implementation with the following comands

Code: Select all

    @Dn
    @Format
    @Dir
    @Save
    @ASave
    @Write
    @Load
    @Run
    @Aload
    @Kill
    @Quit
    @ACopy
    @CassCopy

there is an EEPROM dump here https://archive.org/details/triton-qd-c-64 which we can pull apart and work out the drive routines from. I will try and have a look at it soonish and explain all the C64 stuff such as BASIC command injection and C64 Memory Map etc so we can then get down to the raw commands.

[TakuikaNinja]

Said drive supports quite a few home computers: C64, Sinclair ZX Spectrum, MSX, Mattel Aquarius, and the Dragon 64.
https://en.wikipedia.org/wiki/Triton_Quick_Disk_Drive

[Oziphantom]

yeah but those have Z80 roms and why would you, well except the Dragon but good luck finding one of those dumped. Kinda odd they didn't support the Coco if you support the Dragon though. And if they have 6502 versions why not an Electron, it would have been a solid upgrade for them.

[Pokun]

According to Wikipedia and its sources, disk capacity for that Triton QD drive is 144 kB non-formatted and 100 kB formatted, meaning 50 kB per side when formatted. 144 kB, that's the first time I heard of a QD drive that uses tighter density than the 128 kB per disk the FDS disk drive is capable of.
I'm not sure how they calculate 144 though, according to the referenced Speccy magazine page the specs are like this:
Storage capacity (formatted): 100 kB (2 sides)
Number of sectors: 20 per side
Sector size: 2.5 kB
Data transmission rate: 101.6 kbit/s
Recording density: 4410 BPI

I guess BPI is bit per inch? Or is that byte per inch? Can't find any numbers for FDS disk density.
According to this, QD capacity ranges from 128 to 256 kB.

I doubt Nintendo would have permitted such a flexible structure for the QD even if it was invented before the FDS. Piracy & bootlegging was bad enough with the existing format...

Yeah I guess, since FDS games only uses a save file for writing game progress and registration data to in a fully predictable manner there isn't really any need to be able to expand or delete any files. It's not like the user is allowed to manage files or format disks, and the disk drives are even protected against writing more than a single file.