How did those dual-format Amiga/Atari ST releases actually work?
 

So there are some games that have Amiga and ST versions on the same disk, e.g. Stone Age and there were also several cover disks back in the day that were compatible with Amiga and ST.

In order to be bootable on an Amiga, the first track needs to have a bootblock otherwise this won't work. I guess this is different on the ST because otherwise a dual-format disk wouldn't be possible. But how exactly is it on the ST? How did they make games bootable on the Amiga as well as on the ST? I don't know anything about Atari so maybe someone can explain this to me...

It's an interesting question because the TOS boot sector is side 0, track 0. Which seems to be identical to the Amiga bootblock location. I'd like to know this as well :)

I thought both systems treat side 0 as the opposite side

Thanks! That's a really ingenious way of doing things. Love tricks like that :D

I often wondered about this as well. Once I even had a coverdisk with Amiga, Atari ST, and IBM PC software on it.

The ones that i've looked at don't work like that. Track 0 has a full set of 11 sectors for the Amiga and 9 sectors for the PC/ST.

You can open up a disk sector editor and see this quite easily on the amiga using DF0: and PC0: at the same time.

The rest of the tracks either show up as valid Amiga or valid PC tracks (usually either one side Amiga and the other ST or lower tracks PC and higher tracks (40+) Amiga.

Based on this I can only assume that both treat side 0 as the opposite physical side.

Even though I started the post linked to above... I couldn't recreate a dual format disk with what I understood from the replies. I will one day research it in enough detail to write a dual-format disk.

Since I wrote this Kryoflux and SuperCard Pro + several disk analysis software tools have arrived and I keep meaning to investigate.

Years ago my A500 stopped reading 1 side of disks (I was young and didn't have the skills to fix it).
I created a disk and used a tool to mark all of side 1 in the bitmap as 'used'. It worked.

It allowed me to boot from a minimal single-sided disk that assigned everything to DF1 to continue. I always assumed this is how the ST/Amiga disks worked.

http://eab.abime.net/showthread.php?t=89537

I thought they were just Dual format and the Atari and PC were just on the same format but different folders etc.

I have asked before but could this BootBlock be written on a PC and load on Amiga? Just the BootBlock?

The dual format track has one sector Amiga, and the other in ST/PC format. It's basically an hybrid track.

Doubtful.

It would be the other way around, individual sectors for the ST and PC.

The ST can read physical sectors on a disk, the Amiga can't. The Amiga to read a sector has to read the entire half of the track to get to the individual sectors.

if you copied it on PC with a decent copier if one exists or Atari would the Amiga Bootblock be there just the bootblock?

At least one game did
 

I bought Starglider 2 and played it on my A500 - and the very same day took it to my Atari 520ST-owning friend and watched as a slightly inferior version of the same game booted up.

Whilst technically the same game the sounds were not quite as good on the Atari, but still technically clever stuff.

You bet that if i posted this, it's because i did a check :laughing .

This track is 11 sectors. The first one is an Amiga sector, the 10 others are ST/PC.

(Please note that AUFIT can't see Amiga sectors, only ST/IBM, but the 1st sector is an Amiga one).

Let me show you :

So what would happen if you copied this on an Atari would the Amiga bootblock still be there?

yes, but nothing would ensure it'd still work. It has to be tested.

Thanks for your reply any chance you can try it?