A mixed-format, mixed-architecture, mixed-sided diskette (2008) | Hacker News Reader

A mixed-format, mixed-architecture, mixed-sided diskette (2008)

trixter.oldskool.org

113 pointsbane21 comments

The C64 did not autoboot. You had to type:

  LOAD"*",8

  LOAD "*",8,0
  RUN

as far as creating the original disc, not that hard. format the whole disc for a commodore. use track 18 sector 0 for bam and sector 1 for directory (just one sector). calculate number of tracks needed for commodore program storage. mark the rest of the disk sectors as used.

move the disk to a pc. using a custom program, format the individual tracks not used by the commodore for the pc (do not use the dos format, it would wipe the disk of commodore info). so, the back of the floppy and the tracks not in commodore space. mark the tracks not formatted for pc as bad in the fat sectors on track 1.

http://trixter.oldskool.org/2008/09/28/the-diskette-that-ble...

You could even do three format with IBM, Apple, and Commodore so long as the Apple and Commodore formatting was on flip sides of the disk.

http://trixter.oldskool.org/2008/09/28/the-diskette-that-ble...

close:

  LOAD "*",8,1

or:

  LOAD "*",8
  RUN

The 8 was the drive number, so it could potentially be 9, 10, or 11. The ,1 indicates "reload into the same memory location it was saved from, rather than into the beginning of BASIC."

Typically commercial games used tricks to get an autorun from the ,1 flag (I can't remember how those worked).

They would overwrite the CHROUT vector used to show the "READY." text after loading. So when BASIC wanted to print the "R" it would call CHROUT, which was rerouted to your application's loader. More info is available at the excellent Pagetable blog [1].

[1] http://www.pagetable.com/?p=568

It's a "polyglot floppy"[1]!

Although it's not too hard to guess how it was produced: format the odd tracks in one machine, then do the evens in another, and write the FS structures such that each machine only sees the data it needs, I agree with Trixter that the most interesting part is someone was creative enough to come up with this solution. A great hack in the traditional sense of the word.

[1] According to Google, I may be the first one to use this phrase on the Internet in a non-spam-site way.

I've never heard of this being used for hybrid C64/PC discs before, but the technique itself isn't all that new - as far back as the late 1980s there were dual-format Atari ST and Amiga discs which would work on either system. Some were mounted as cover discs on magazines, and indeed at least one magazine managed a three-way disc that was ST, Amiga and PC compatible.

Some released software was dual-format as well - I particularly recall the Atari ST/Amiga version of Starglider. While the ST and Amiga boxes were both separately labelled, the actual disc inside was the same, and worked on either machine.

This is different.

ST, Amiga and PC all used the same magnetic encoding, called MFM[0], so differences were completely logical (and not even very different - e.g., the ST and PC both used the old CP/M "FAT" format that is still with us today). That was more like having a file that's at the same time a .c program and a shell script. Nice, but at a rather high level of abstraction.

Apple II and the C64 used GCR[1] encodings (not the same GCR encoding), which is completely different. A C64 drive controller cannot read MFM, and a PC disk controller cannot read GCR.

The interesting thing about this hybrid disk is that whoever made it alternated the tracks - odd were GCR, even were MFM, and the logical filesystems were arranged such that each file system respected the other filesystem's tracks.

[0] https://en.wikipedia.org/wiki/Modified_Frequency_Modulation

[1] https://en.wikipedia.org/wiki/Group_code_recording

Yes, of course, understood and accepted - this is cool too.

The C64/PC disc discussed here is also from the late 80s.

I bought an Atari St 1040 something in college, with a dot matrix printer. I told no one, except my girlfriend, about my computer. I literally felt like I was cheating. I only used it for word processing, but it saved so much time. I don't think I would have graduated, if I didn't have that Atarti St?

When I tried to sell my girlfriend on the computer; she just wasen't interested. "I will pay someone to type my papers. It's not that expensive. I got the brilliant notion, I would play to her creative side. I opened the paint(forget the name of the graphics program), and drew an erotic picture on the screen. Well that sealed the deal, "Put that computer away, or you will never get to see my erotic parts!" Never again told a single person about my cheating devise. Threw it away after a nervous breakdown in graduate school. I still miss that dot matrix printer--that lasted years on the same ribbon? I think I bought maybe one ribbon, and it was cheap?

Hope your doing well Ingrid?

You must have been swimming in money. College students, throwing entire computers away in the 1980s.

When I was 17 I remember having my mind blown that you could use a hole punch to double the storage space on your existing media. In a way, these type of hardware hacks put you more in touch with the devices you were using.

Day-before-yesterday I put a memory card in the DVD slot on my iMac. I have no clue how I'm going to get it out, other than taking apart my computer. Or leaving it there, given I don't use DVDs anymore.

I once absentmindedly put one of those small CDs into a slot drive in a laptop... Taking the laptop wasn't a problem, but taking the slot drive apart?

It makes me sad that everything is built to keep you out of your devices.

Making things compact and precise is hard.

A full sized disc drive is only a moment of screwing to open up.

This non-slot laptop drive I have seems to be easy to disassemble too.

Slot drives cannot handle mini CD's? https://en.wikipedia.org/wiki/Mini_CD

It's right in your wikipedia link "Most slot-loading CD drives are generally incompatible..."

There were purpose built 5.25" diskette punches. I still have one. For those who don't know how such a contraption looks, Wikipedia has at least an image [1], but no article in English unfortunately.

[1] https://commons.wikimedia.org/wiki/Diskette#/media/File:Disk...

https://en.wikipedia.org/w/index.php?title=Floppy_disk_varia...

yeah... I remember buying higher quality disks, that were marked for lower density and single sided (forget the brand) and discovering that you could punch and format double sided, double density without issue... jackpot!

It would have been hard to imagine these days having a stack of thumb drives and digging for one at least 8gb, and thinking, when I saw the 512mb-2gb ones of just tossing them away.

closest thing today that I can think of is buying one of those fake chinese 128GB USB drives on ebay/alibaba, running h2testw to determine its really 8GB, making a screenshot and starting a refund claim - bam a free 8GB usb drive.

Use a thin L-shaped piece of cardboard to fish it out. I used the top flap of a cereal box, folded in half. The tab on the flap was big enough to hook onto the SD card.

Now that's cost saving.

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