Question about NDOS, Trackloaders, BootSectors etc

trackah123 · 26 February 2008, 09:43

Hi Guys.

Hopefully i put it in the right forum-section and allowed to ask.

I have a question about the so called "NDOS" disks (Non-DOS) on Amiga. I never really understood them.

Experimenting with several programs i know it is some sort of custom File System and the Boot Sector (Sector 0 or 40) is used for booting and regonizing that filesystem? i think.

What kind of NDOS Filesystem exists on the Amiga? are these a few. Or did every game-company programmed there own customized File System?

I am almost sure during the development they created it on a standard OFS or FFS AmigaOS Filesystem.. but once they are finished they convert it somehow to this hidden customized NDOS Filesystem, probably to protect it better. I find this very interesting. I think workbench can read those disks if it knows how to regonize and control that filesystem with some sort of library or drive.

Like CrossDos for example it knows how to read FAT filesystem on workbench once you started CrossDos and mount PC0.

In the past i managed it once to convert a game back to OFS so i could read out all files in workbench.. This game was NDOS before.. and even when converting it back it still booted. I only managed to do this once.. I believe i did it with X-Copy Sector 0-40 or Viruscope 1.0 or some sort of Diskblock editor cant remember its been a while.

My intention is nothing related to copying or anything bad like that. Just to understand and hopefully learn a bit about those NDOS filesystems, bootsectors, trackloaders etc.

I hope anyone here can tell me a bit about it. Because i find this very interesting

girv · 26 February 2008, 10:29

The first two sectors on a floppy are the boot sectors. If these are set up with the correct header and checksum, the Amiga will run the code they contain at boot time.

NDOS just means "Not DOS", and doesn't specify anything further than that. Most NDOS disks use a loading system completely custom to themselves, though there are a few software companies that used the same system on multiple titles. Psygnosis and Gremlin spring to mind, but there are others. Check out the docs for WWarp for a few of the common ones.

The custom loading systems are usually very simple and it would be a stretch to call them "file systems". Typically they will just access data by length and track / sector number - "load 10 sectors from track 15" rather than "load file x". Some are more complex though and do use actual filenames, and for these it would be possible to write a driver to access the files from Workbench (like CrossDOS). But as the formats are all different it would only be useful for that one disk or a few at best.

"Imager Slaves" from the WHDLoad project are kind of like this and can extract the contents of custom filesystem game disks to regular files on your hard drive, but the slave is specially written for each game.

You can make a disk NDOS by breaking a few checksums or sectors while leaving the majority of the disk actually in DOS format. This technique is used as a simple form of copy protection. I'd guess this was the case for the disk you converted back to OFS, and the utility you used just fixed the (intentional) errors to make it a normal disk again.

Hope that helps

trackah123 · 26 February 2008, 12:31

Interesting thanks.

Is there a link for this "Imager Slaves from the WHDLoad project Extractor"

Link to "docs for WWarp" also.

Links for non-WHDLoad related extractors for the Amiga? if any.

Quote:

You can make a disk NDOS by breaking a few checksums or sectors while leaving the majority of the disk actually in DOS format

Yes thats probably what i did by accident with that particular game (It was the Alien Breed II Demo disk from Team17).

btw I never knew the bootsectors were the first 2 sectors.. i always thought only sector 1

Or do you mean by the first 2 sectors like cylinder 0 and cylinder 40 of a disk (of the total of 80 cylinders)

And Sector 40 for regonition of the trackloader or filesystem. Is it only Sector 40 or also sectors near 40.

This morning i formatted sector 40 while leaving sector 0 and 1 intact.. it would still boot.. but in workbench the disk was empty lol.. not NDOS anymore. Still could not see any files on it.

Note : Im not trying to crack games or piracy stuff or anything bad, dont get me wrong. Just interested in converting between NDOS and OFS/FFS.

Maybe 1 day i can make my own bootloader NDOS system for my demos i make with Red Sector Demomaker. Because the Red Sector Demomaker can only write 1 demo in NDOS mode. And i want to make some sort of megademo so that more small demofiles run after eachother in NDOS.

I'm not a coder but i think you need codeskills for this.

girv · 26 February 2008, 13:20

Quote:

Originally Posted by trackah123

Is there a link for this "Imager Slaves from the WHDLoad project Extractor" Link to "docs for WWarp" also.

http://www.whdload.de

WWarp is part of WHDLoad. IIRC it is included in the download archive on that page. Imager slaves are plugin style things for the RawDIC program, also part of WHDLoad.

Quote:

Originally Posted by trackah123

Links for non-WHDLoad related extractors for the Amiga? if any.

Dunno about those. I think possibly WWarp can extract files from some formats, but I'm barely 48% sure about that. It's not a program I use very often

Quote:

Originally Posted by trackah123

btw I never knew the bootsectors were the first 2 sectors.. i always thought only sector 1

Or do you mean by the first 2 sectors like cylinder 0 and cylinder 40 of a disk (of the total of 80 cylinders)

And Sector 40 for regonition of the trackloader or filesystem. Is it only Sector 40 or also sectors near 40.

This morning i formatted sector 40 while leaving sector 0 and 1 intact.. it would still boot.. but in workbench the disk was empty lol.. not NDOS anymore. Still could not see any files on it.

I think you're getting "sector" and "track" confused.

A disk has 40 cylinders, each has two tracks (one on each side), and each DOS track has 11 512 byte sectors. A sector is just a conceptual way of organising data on a track, so custom formats may have more or less sectors of different length. There is also an upper limit on the total data length of a track.

The first two sectors of track 0 (= first cylinder, first side) are the boot sectors. Track 0 has to be in standard DOS format to be bootable, as the OS (Kickstart, actually) wouldn't know how to read the bootsectors otherwise.

Track (not sector) 40 on a DOS disk is the rootblock, which contains information that allows the OS to recognise it as a standard disk. By formatting it you wiped the links to the contents of the disk, hence it appeared empty to Workbench.

http://www.amigau.com/aig/adfaq.html ... contains lots of juicy details for you

Quote:

Originally Posted by trackah123

Just interested in converting between NDOS and OFS/FFS.

I don't mean to rain on your parade, but in the general case that won't be possible

dlfrsilver · 26 February 2008, 13:41

Oh yes it can girv, but it requires to crack pure and simple the disk system.
in order to get the files.....and do the conversion.

Toni Wilen · 26 February 2008, 13:47

"Officially" it is 160 tracks and 80 cylinders (cylinders = tracks * heads) but everyone usually just says 80 tracks. It can get confusing

EDIT: Do not read this. See following posts.

girv · 26 February 2008, 13:56

Quote:

Originally Posted by dlfrsilver

Oh yes it can girv, but it requires to crack pure and simple the disk system. in order to get the files.....and do the conversion.

Sorry, I wasn't very clear there.

I meant that in most cases there are no "files" in the normal sense, just lists of startpoint,length. I guess those could be considered files though

girv · 26 February 2008, 13:59

Quote:

Originally Posted by Toni Wilen

"Officially" it is 160 tracks and 80 cylinders (cylinders = tracks * heads) but everyone usually just says 80 tracks. It can get confusing

Absolutely correct. Don't know what I was on before

I think I meant 80 cylinders, not 40. Not enough coffee in the world for me today, I think

eLowar · 26 February 2008, 14:02

Quote:

Originally Posted by Toni Wilen

"Officially" it is 160 tracks and 80 cylinders (cylinders = tracks * heads) but everyone usually just says 80 tracks. It can get confusing

That can't be right...

cylinders = tracks * heads

80 = 160 * heads

That'd mean there's half a head? I'd correct it, but the simple fact is that I don't really have a clue.

girv · 26 February 2008, 14:10

tracks = cylinders * heads ?

Toni Wilen · 26 February 2008, 14:46

Tracks = Cylinders * Heads, Cylinders = Tracks / heads. (Regular DD floppy Cylinders=80, Tracks=160, Heads=2)

I am too tired today..

trackah123 · 26 February 2008, 16:09

http://en.wikipedia.org/wiki/Amiga_Old_File_System

Quote:

The geometry of an Amiga Floppy Disk is as follows:

DD disks: 512 bytes/sector, 11 sector/track, 2 track/cyl, 80 cyl/disk
HD disks: 512 bytes/sector, 22 sector/track, 2 track/cyl, 80 cyl/disk

The DD disk has 11 * 2 * 80 = 1760 (0 to 1759) blocks, while the HD disk has 22 * 2 * 80 = 3520 blocks.
Amiga stores 880 KiB on a DD disk and 1760 KiB on an HD floppy disk.

Same discussion i have on amiga.org, link below
http://www.amiga.org/modules/newbb/v...43712&forum=22

Some other interesting links i got from amiga.org

http://mediasrv.ns.ac.yu/extra/filef...or/adf/adf.txt
http://lclevy.free.fr/adflib/adf_info.html

interesting

i'm going to try that wwarp for now.

NOB · 26 February 2008, 21:45

Which is the theoretical maximum of bits that could be physically written on a track?
(MFM format including clockbits)

IFW · 27 February 2008, 03:30

About 111200 bits are readable by the amiga fdc max, but you are really pushing your luck with that, and a slightly misaligned drive won't be able to read that.

trackah123 · 27 February 2008, 07:22

I wonder how much data can fit onto a 880kb floppy. i remember this demo from Virtual Dreams/Fairlight 242 where they compressed like a 24MB movie onto 880kb. and thats pretty sick crunching techniques if you tell me.

How much uncompressed data would fit at max if you take as much cylinders as possible (more then 80). and making maximal use of de fdc (bits per track)? So that it still can be read by regular Amiga's without getting sync or misalign problems? I wonder if it can be pushed to 1MB disk then?

dlfrsilver · 27 February 2008, 09:51

easily more than 1mb. games like turrican or BCkid for example are more than 1mb stuck on 1 disk.

Galahad/FLT · 27 February 2008, 09:52

Factor 5's disk format, some of the Psygnosis disk formats are all pretty large disk capacity.

trackah123 · 27 February 2008, 10:17

Sounds incredible to almost make a HD floppy capacity on a DD floppy

Retro1234 · 27 February 2008, 10:20

Could you just mount a Amiga Filesystem in Workbench but that just misses track 40 creating a NDOS disk but reads all other tracks?

What would you say was the most MB was that could be fitted on a Amiga floppy?

NOB · 27 February 2008, 21:03

@ IFW: thanks, interesting info.

Can this size (111200) increase about 20% on a long track(copyprotection)?
And which game has the largest longtrack?

Referring to a floppy book a standard track has ca. 101312 bits (including
gap of 696 bytes).
This means ca. 9% of the track capacity are not used.This seems to be the price for data safety?

26 February 2008, 09:43	#1
trackah123 Amiga User Join Date: Dec 2006 Location: Delft / The Netherlands Posts: 327	Question about NDOS, Trackloaders, BootSectors etc Hi Guys. Hopefully i put it in the right forum-section and allowed to ask. I have a question about the so called "NDOS" disks (Non-DOS) on Amiga. I never really understood them. Experimenting with several programs i know it is some sort of custom File System and the Boot Sector (Sector 0 or 40) is used for booting and regonizing that filesystem? i think. What kind of NDOS Filesystem exists on the Amiga? are these a few. Or did every game-company programmed there own customized File System? I am almost sure during the development they created it on a standard OFS or FFS AmigaOS Filesystem.. but once they are finished they convert it somehow to this hidden customized NDOS Filesystem, probably to protect it better. I find this very interesting. I think workbench can read those disks if it knows how to regonize and control that filesystem with some sort of library or drive. Like CrossDos for example it knows how to read FAT filesystem on workbench once you started CrossDos and mount PC0. In the past i managed it once to convert a game back to OFS so i could read out all files in workbench.. This game was NDOS before.. and even when converting it back it still booted. I only managed to do this once.. I believe i did it with X-Copy Sector 0-40 or Viruscope 1.0 or some sort of Diskblock editor cant remember its been a while. My intention is nothing related to copying or anything bad like that. Just to understand and hopefully learn a bit about those NDOS filesystems, bootsectors, trackloaders etc. I hope anyone here can tell me a bit about it. Because i find this very interesting

26 February 2008, 13:47	#6
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,529	"Officially" it is 160 tracks and 80 cylinders (cylinders = tracks * heads) but everyone usually just says 80 tracks. It can get confusing EDIT: Do not read this. See following posts. Last edited by Toni Wilen; 26 February 2008 at 14:50. Reason: buggy post

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26 February 2008, 10:29	#2
girv Mostly Harmless Join Date: Aug 2004 Location: Northern Ireland Posts: 1,115	The first two sectors on a floppy are the boot sectors. If these are set up with the correct header and checksum, the Amiga will run the code they contain at boot time. NDOS just means "Not DOS", and doesn't specify anything further than that. Most NDOS disks use a loading system completely custom to themselves, though there are a few software companies that used the same system on multiple titles. Psygnosis and Gremlin spring to mind, but there are others. Check out the docs for WWarp for a few of the common ones. The custom loading systems are usually very simple and it would be a stretch to call them "file systems". Typically they will just access data by length and track / sector number - "load 10 sectors from track 15" rather than "load file x". Some are more complex though and do use actual filenames, and for these it would be possible to write a driver to access the files from Workbench (like CrossDOS). But as the formats are all different it would only be useful for that one disk or a few at best. "Imager Slaves" from the WHDLoad project are kind of like this and can extract the contents of custom filesystem game disks to regular files on your hard drive, but the slave is specially written for each game. You can make a disk NDOS by breaking a few checksums or sectors while leaving the majority of the disk actually in DOS format. This technique is used as a simple form of copy protection. I'd guess this was the case for the disk you converted back to OFS, and the utility you used just fixed the (intentional) errors to make it a normal disk again. Hope that helps

26 February 2008, 13:41	#5
dlfrsilver CaptainM68K-SPS France Join Date: Dec 2004 Location: Melun nearby Paris/France Age: 46 Posts: 10,457	Oh yes it can girv, but it requires to crack pure and simple the disk system. in order to get the files.....and do the conversion.

26 February 2008, 14:10	#10
girv Mostly Harmless Join Date: Aug 2004 Location: Northern Ireland Posts: 1,115	tracks = cylinders * heads ?

26 February 2008, 14:46	#11
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,529	Tracks = Cylinders * Heads, Cylinders = Tracks / heads. (Regular DD floppy Cylinders=80, Tracks=160, Heads=2) I am too tired today..

26 February 2008, 21:45	#13
NOB Zone Friend Join Date: Aug 2005 Location: Germany Age: 52 Posts: 424	Which is the theoretical maximum of bits that could be physically written on a track? (MFM format including clockbits)

27 February 2008, 03:30	#14
IFW Moderator Join Date: Jan 2003 Location: ... Age: 52 Posts: 1,838	About 111200 bits are readable by the amiga fdc max, but you are really pushing your luck with that, and a slightly misaligned drive won't be able to read that.

27 February 2008, 07:22	#15
trackah123 Amiga User Join Date: Dec 2006 Location: Delft / The Netherlands Posts: 327	I wonder how much data can fit onto a 880kb floppy. i remember this demo from Virtual Dreams/Fairlight 242 where they compressed like a 24MB movie onto 880kb. and thats pretty sick crunching techniques if you tell me. How much uncompressed data would fit at max if you take as much cylinders as possible (more then 80). and making maximal use of de fdc (bits per track)? So that it still can be read by regular Amiga's without getting sync or misalign problems? I wonder if it can be pushed to 1MB disk then?

27 February 2008, 09:51	#16
dlfrsilver CaptainM68K-SPS France Join Date: Dec 2004 Location: Melun nearby Paris/France Age: 46 Posts: 10,457	easily more than 1mb. games like turrican or BCkid for example are more than 1mb stuck on 1 disk.

27 February 2008, 09:52	#17
Galahad/FLT Going nowhere Join Date: Oct 2001 Location: United Kingdom Age: 50 Posts: 9,012	Factor 5's disk format, some of the Psygnosis disk formats are all pretty large disk capacity.

27 February 2008, 10:17	#18
trackah123 Amiga User Join Date: Dec 2006 Location: Delft / The Netherlands Posts: 327	Sounds incredible to almost make a HD floppy capacity on a DD floppy

27 February 2008, 10:20	#19
Retro1234 Phone Homer Join Date: Jun 2006 Location: 5150 Posts: 5,786	Could you just mount a Amiga Filesystem in Workbench but that just misses track 40 creating a NDOS disk but reads all other tracks? What would you say was the most MB was that could be fitted on a Amiga floppy?

27 February 2008, 21:03	#20
NOB Zone Friend Join Date: Aug 2005 Location: Germany Age: 52 Posts: 424	@ IFW: thanks, interesting info. Can this size (111200) increase about 20% on a long track(copyprotection)? And which game has the largest longtrack? Referring to a floppy book a standard track has ca. 101312 bits (including gap of 696 bytes). This means ca. 9% of the track capacity are not used.This seems to be the price for data safety?

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