

A mixed-format, mixed-architecture, mixed-sided diskette (2008) - bane
http://trixter.oldskool.org/2008/09/28/the-diskette-that-blew-trixters-mind/

======
mmphosis
The C64 did not autoboot. You had to type:

    
    
      LOAD"*",8
    

or

    
    
      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...](http://trixter.oldskool.org/2008/09/28/the-diskette-that-blew-
trixters-mind/#comment-7310)

 _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...](http://trixter.oldskool.org/2008/09/28/the-diskette-that-blew-
trixters-mind/#comment-7321)

~~~
chillingeffect
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).

~~~
royjacobs
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](http://www.pagetable.com/?p=568)

------
userbinator
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.

------
jamesbrownuhh
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.

~~~
beagle3
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](https://en.wikipedia.org/wiki/Modified_Frequency_Modulation)

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

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

------
kordless
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.

~~~
therealidiot
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.

~~~
listic
Slot drives cannot handle mini CD's?
[https://en.wikipedia.org/wiki/Mini_CD](https://en.wikipedia.org/wiki/Mini_CD)

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

------
digi_owl
Now that's cost saving.

