Technical: Dual Format disks?

alexh · 07 March 2008, 11:19

I am sure we're all familiar with Dual format floppy disks. Back in the late 80's some cunning people (including Rob Northern Computing) wondered if it would be possible to get the Atari ST and the Amiga to boot from the same disk (afterall they used the same physical medium).

The results were a success and 10's of game disks and 100's of magazine coverdisks were produced in Dual-Format.

To name but a handful:

Lethal Xcess,
Monster Business,
Starglider 2,
Stunt Car Racer,
Bionic Commando,
3D-Pool,
Carrier Command,
Zero Magazine,
ST-Amiga Format Magazine
"The One For 16-bit games" Magazine
etc.etc.

Rick Dangerous II (KIXX) is Tri-Format supporting Atari-ST, Amiga and PC on one disk!

What I am wondering is how they did this (technically?) I doubt they used physically different track layouts, data super imposed or anything like that did they? I suspect they just divided the disk into two (or more) regions and put the Amiga code and data in one half and the Atari ST (or PC) data in the other half. (Perhaps putting common data like gfx in a common area).

The smart bit was obviously booting.

Do all 3 (Amiga, ST and PC) all read the same physical boot track/sector? And read off the same data?

I can sort of understand Atari-ST/Amiga. They both have 68k CPU's and so if they both read binary off a disk and it was just raw 68k instructions and data there is a chance you could add a detection code that worked on both and branched appropriately to load different data.

But 68k and x86?

What did the developers do? Scour the 68k / x86 opcodes until they found some that would be relatively harmless to each other but produce the desired effect?

If anyone knows the history and technical information I'd really like to know.

I think my understanding of how floppy disks work is quite naive. I am sure they are not quite block level devices like hard drives. I never quite grasped the concept of MFM at the lowest level, never understood half of the options in X-Copy, Sync (4489!?) etc.

Be very interesting to know.

Charlie · 07 March 2008, 11:59

I don't have a useful answer but your question made me go 'Hmmm, I wonder...'

Rob Northen is, as you say, the chap who came up with a tri-boot block for Amiga/ST/x86 discs.
I've no idea how he did it - though I'd also be interested to know. Rick Dangerous specifically used his code...
...maybe will jog a few memories somewhere and get you (and me) an answer.

Predseda · 07 March 2008, 12:00

Populous - the Promised lands is another example

Mick_AKA · 07 March 2008, 12:59

My copy of Gunship is dual format Amiga/PC

I also always wondered how this was done!

Toni Wilen · 07 March 2008, 13:21

It isn't very complex. Following explanation ignores MFM level stuff because it would only cause even more confusion

Basically at least track zero has "interleaved" data. This way both Amiga and Atari ST can see normal looking track with correct system specific boot sector(s).

For example if you check bootblock of dualformat disk with disk editor, you will see normal Amiga boot block and random looking data on other track zero sectors. This "random data" is part of specially positioned Atari ST data.

Positioning of MFM syncwords, format identifiers and checksums is the tricky part.

r.cade · 07 March 2008, 14:44

On the C64, this was done between Atari and C64.

The way it worked there was there were no track collisions- Atari boots from track 1 and C64 boots from track 18. Some tracks were FM (for Atari) and some were GCR (for the C64) and they just appeared as garbage to the other computer.

The Atari/Amiga/PC would be more complicated, because they all need track 1 (or is it called track 0 on those systems?)

alexh · 07 March 2008, 15:23

Quote:

Originally Posted by Toni Wilen

Basically at least track zero has "interleaved" data. This way both Amiga and Atari ST can see normal looking track with correct system specific boot sector(s).

It's this "interleaving" which is the bit that interests me. They dont try to read the same data from track 0, sector 0 then?

Quote:

Originally Posted by Toni Wilen

For example if you check bootblock of dualformat disk with disk editor, you will see normal Amiga boot block and random looking data on other track zero sectors. This "random data" is part of specially positioned Atari ST data. Positioning of MFM syncwords, format identifiers and checksums is the tricky part.

And it's these MFM syncwords (the 0x4489 in the bitstream), which make the two (or more) systems read different data?

But dont PC's and Amiga's both use the same sync marks?

I think I need to brush up

http://www.softpres.org/wip:2002-07-18
http://cyberpingui.free.fr/tuto_trackloader.htm

Toni Wilen · 07 March 2008, 15:49

Quote:

Originally Posted by alexh

It's this "interleaving" which is the bit that interests me. They dont try to read the same data from track 0, sector 0 then?

I am not sure about PC sectors but at least Amiga sector zero can be anywhere.

Quote:

And it's these MFM syncwords (the 0x4489 in the bitstream), which make the two (or more) systems read different data?

But dont PC's and Amiga's both use the same sync marks?

Yes but PC needs more than just 0x4489 before it starts reading. (reason why only 2-drive trick can read Amiga disks)

IFW · 07 March 2008, 16:54

A hw mfm controller is triggered by 3 consecutive marks.
There are many ways you can do this.
One is to start an ST block embedded into a longer Amiga one's data area and then interleave accordingly.

For the Amiga it will be unused data and vice versa.
You just have to make sure that the various bootblocks and entries are valid when read on different platforms.

Same about tri-format.

alexh · 26 July 2011, 10:32

Reviving an old thread, anyone have a definitive list of Dual and Tri format disks?? There is some info on HOL but it is not easily filtered on.

Action Fighter (Amiga/PC dual-format disk)
Lethal Xcess - Wings of Death II (Amiga/Atart ST dual-format disks)
Monster Business (Amiga/Atari ST dual-format disk)
Populous: The Promised Lands (Amiga/Atari ST dual-format disk)
Rick Dangerous Kixx (Amiga/PC dual-format disk)
Rick Dangerous 2 Kixx (Amiga/PC dual-format disk)
Stone Age (Amiga/Atari ST dual-format disk)
Street Fighter (Amiga/PC dual-format disk)
StarGlider 2 (Amiga/Atari ST dual-format disk)
3D Pool (Amiga/Atari ST/PC tri-format disk)
Stunt Car Racer Kixx (Amiga/PC dual-format disk)
Bionic Commando Kixx (Amiga/PC dual-format disk)
Carrier Command Kixx (Amiga/PC dual-format disk)
Blasteroids Kixx (Amiga//PC dual-format disk)
E-Motion Kixx (Amiga//PC dual-format disk)
Indiana Jones and the Last Crusade Action Kixx (Amiga//PC dual-format disk)
Out Run Kixx (Amiga/PC dual-format disk)
World Class Leader Board Kixx (Amiga/PC dual-format disk)
International Soccer Challenge Kixx (Amiga/PC dual-format disk)
MicroProse Soccer Kixx (Amiga/PC dual-format disk)

mr.vince · 26 July 2011, 14:19

Thanks! Since there are so many not yet properly archived, I'd like to point out that an IPF can store such information. So anyone having one of the titles not dumped yet (please see http://www.softpres.org/games for ones already ingested) please let us know.

alexh · 26 July 2011, 16:26

There are also one or two ST/Amiga format disks which were dual format, Zero Magazine and one or two others.

I have quite a few of these titles I can dump but I'm sure EAB threads said they had been dumped before.

E.G. Stunt Car Racer Kixx

Do they need re-dumping with the latest software?

Retro1234 · 26 July 2011, 16:52

I wouldnt mind a dump of a coverdisk if anyone can eADF should do?

Is there a max size per Format? In layman's terms how can you have Atari Bootblock and Amiga.

alexh · 26 July 2011, 18:01

The ST/Amiga dual format disks are available on AMR

Quote:

Originally Posted by Boo Boo

In layman's terms how can you have Atari Bootblock and Amiga.

Read above.

Quote:

Originally Posted by IFW

A hw mfm controller is triggered by 3 consecutive marks.
There are many ways you can do this.
One is to start an ST block embedded into a longer Amiga one's data area and then interleave accordingly.

For the Amiga it will be unused data and vice versa.
You just have to make sure that the various bootblocks and entries are valid when read on different platforms.

Retro1234 · 26 July 2011, 18:11

As far as I know the and I havent checked them all the disk on AMR are ADFs so only Amiga Format.

It might be hard to understand my motivation

for such a question but if I created a blank .ST file and copied the Bootblock from a Dual Format disk to it

I should be able to write this on a ST maybe even PC would the Amiga BootBlock still boot I dont expect anything happen more than this.

alexh · 26 July 2011, 18:26

Not that I know of.

Until one of the ST emulators gets IPF support I think you're stuffed. Hatari and STeEM are opensource so they could in theory get the SPS DLL support.

I don't think you could use WinUAE with the SPS DLL to make a .ST image from the IPF file but you never know.

I think there are already .ST images of the Amiga/ST format disks.

http://www.stformat.com

07 March 2008, 11:19	#1
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,396	Technical: Dual Format disks? I am sure we're all familiar with Dual format floppy disks. Back in the late 80's some cunning people (including Rob Northern Computing) wondered if it would be possible to get the Atari ST and the Amiga to boot from the same disk (afterall they used the same physical medium). The results were a success and 10's of game disks and 100's of magazine coverdisks were produced in Dual-Format. To name but a handful: Lethal Xcess, Monster Business, Starglider 2, Stunt Car Racer, Bionic Commando, 3D-Pool, Carrier Command, Zero Magazine, ST-Amiga Format Magazine "The One For 16-bit games" Magazine etc.etc. Rick Dangerous II (KIXX) is Tri-Format supporting Atari-ST, Amiga and PC on one disk! What I am wondering is how they did this (technically?) I doubt they used physically different track layouts, data super imposed or anything like that did they? I suspect they just divided the disk into two (or more) regions and put the Amiga code and data in one half and the Atari ST (or PC) data in the other half. (Perhaps putting common data like gfx in a common area). The smart bit was obviously booting. Do all 3 (Amiga, ST and PC) all read the same physical boot track/sector? And read off the same data? I can sort of understand Atari-ST/Amiga. They both have 68k CPU's and so if they both read binary off a disk and it was just raw 68k instructions and data there is a chance you could add a detection code that worked on both and branched appropriately to load different data. But 68k and x86? What did the developers do? Scour the 68k / x86 opcodes until they found some that would be relatively harmless to each other but produce the desired effect? If anyone knows the history and technical information I'd really like to know. I think my understanding of how floppy disks work is quite naive. I am sure they are not quite block level devices like hard drives. I never quite grasped the concept of MFM at the lowest level, never understood half of the options in X-Copy, Sync (4489!?) etc. Be very interesting to know.

07 March 2008, 11:59	#2
Charlie . . Mouse . . Join Date: Jun 2005 Location: Nowhere Age: 55 Posts: 1,792	I don't have a useful answer but your question made me go 'Hmmm, I wonder...' Rob Northen is, as you say, the chap who came up with a tri-boot block for Amiga/ST/x86 discs. I've no idea how he did it - though I'd also be interested to know. Rick Dangerous specifically used his code... ...maybe will jog a few memories somewhere and get you (and me) an answer. Last edited by Charlie; 07 March 2008 at 12:05.

26 July 2011, 10:32	#10
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,396	Reviving an old thread, anyone have a definitive list of Dual and Tri format disks?? There is some info on HOL but it is not easily filtered on. Action Fighter (Amiga/PC dual-format disk) Lethal Xcess - Wings of Death II (Amiga/Atart ST dual-format disks) Monster Business (Amiga/Atari ST dual-format disk) Populous: The Promised Lands (Amiga/Atari ST dual-format disk) Rick Dangerous Kixx (Amiga/PC dual-format disk) Rick Dangerous 2 Kixx (Amiga/PC dual-format disk) Stone Age (Amiga/Atari ST dual-format disk) Street Fighter (Amiga/PC dual-format disk) StarGlider 2 (Amiga/Atari ST dual-format disk) 3D Pool (Amiga/Atari ST/PC tri-format disk) Stunt Car Racer Kixx (Amiga/PC dual-format disk) Bionic Commando Kixx (Amiga/PC dual-format disk) Carrier Command Kixx (Amiga/PC dual-format disk) Blasteroids Kixx (Amiga//PC dual-format disk) E-Motion Kixx (Amiga//PC dual-format disk) Indiana Jones and the Last Crusade Action Kixx (Amiga//PC dual-format disk) Out Run Kixx (Amiga/PC dual-format disk) World Class Leader Board Kixx (Amiga/PC dual-format disk) International Soccer Challenge Kixx (Amiga/PC dual-format disk) MicroProse Soccer Kixx (Amiga/PC dual-format disk) Last edited by alexh; 26 July 2011 at 16:31.

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07 March 2008, 12:00	#3
Predseda Puttymoon inhabitant Join Date: Mar 2007 Location: Tromaville Age: 46 Posts: 7,551	Populous - the Promised lands is another example

07 March 2008, 12:59	#4
Mick_AKA crusader of light Join Date: Jul 2002 Location: Stone, Staffordshire. Posts: 1,151	My copy of Gunship is dual format Amiga/PC I also always wondered how this was done!

07 March 2008, 13:21	#5
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,534	It isn't very complex. Following explanation ignores MFM level stuff because it would only cause even more confusion Basically at least track zero has "interleaved" data. This way both Amiga and Atari ST can see normal looking track with correct system specific boot sector(s). For example if you check bootblock of dualformat disk with disk editor, you will see normal Amiga boot block and random looking data on other track zero sectors. This "random data" is part of specially positioned Atari ST data. Positioning of MFM syncwords, format identifiers and checksums is the tricky part.

07 March 2008, 14:44	#6
r.cade Registered User Join Date: Aug 2006 Location: Augusta, Georgia, USA Posts: 550	On the C64, this was done between Atari and C64. The way it worked there was there were no track collisions- Atari boots from track 1 and C64 boots from track 18. Some tracks were FM (for Atari) and some were GCR (for the C64) and they just appeared as garbage to the other computer. The Atari/Amiga/PC would be more complicated, because they all need track 1 (or is it called track 0 on those systems?)

07 March 2008, 16:54	#9
IFW Moderator Join Date: Jan 2003 Location: ... Age: 52 Posts: 1,838	A hw mfm controller is triggered by 3 consecutive marks. There are many ways you can do this. One is to start an ST block embedded into a longer Amiga one's data area and then interleave accordingly. For the Amiga it will be unused data and vice versa. You just have to make sure that the various bootblocks and entries are valid when read on different platforms. Same about tri-format.

26 July 2011, 14:19	#11
mr.vince Cheesy crust Join Date: Nov 2008 Location: Hawk's Creek Age: 48 Posts: 1,383	Thanks! Since there are so many not yet properly archived, I'd like to point out that an IPF can store such information. So anyone having one of the titles not dumped yet (please see http://www.softpres.org/games for ones already ingested) please let us know.

26 July 2011, 16:26	#12
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,396	There are also one or two ST/Amiga format disks which were dual format, Zero Magazine and one or two others. I have quite a few of these titles I can dump but I'm sure EAB threads said they had been dumped before. E.G. Stunt Car Racer Kixx Do they need re-dumping with the latest software?

26 July 2011, 16:52	#13
Retro1234 Phone Homer Join Date: Jun 2006 Location: 5150 Posts: 5,789	I wouldnt mind a dump of a coverdisk if anyone can eADF should do? Is there a max size per Format? In layman's terms how can you have Atari Bootblock and Amiga.

26 July 2011, 18:11	#15
Retro1234 Phone Homer Join Date: Jun 2006 Location: 5150 Posts: 5,789	As far as I know the and I havent checked them all the disk on AMR are ADFs so only Amiga Format. It might be hard to understand my motivation for such a question but if I created a blank .ST file and copied the Bootblock from a Dual Format disk to it I should be able to write this on a ST maybe even PC would the Amiga BootBlock still boot I dont expect anything happen more than this.

26 July 2011, 18:26	#16
alexh Thalion Webshrine Join Date: Jan 2004 Location: Oxford Posts: 14,396	Not that I know of. Until one of the ST emulators gets IPF support I think you're stuffed. Hatari and STeEM are opensource so they could in theory get the SPS DLL support. I don't think you could use WinUAE with the SPS DLL to make a .ST image from the IPF file but you never know. I think there are already .ST images of the Amiga/ST format disks. http://www.stformat.com

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