Disk Nibbling

[msh5150]

Hi everyone - it's my first time on this board...

I've been wondering what exactly "nibble copying" is and how it works.

I'm a coder and know the normal usage of DSKSYNC etc and how NDOS trackloaders work (I've coded a few myself) - but I've been getting more into cracking/copy protection (just for my own amusement - not spreading 'warez') since the CAPS images became more available.

It seems to me the biggest problems are finding the tracksync mark (especially if it's not $4489) and working out how long the track is?  :-o

As long as those problems are solved there is no reason to decode the MFM?

Any help would be great guys...

[msh5150]

Thanks for your advice guys.  I did a similar post to this one on English Amiga Board and didn't get a single reply  :-(   But then I heard that the more 'techy' users hang out on this board so I tried my luck  :-D

@Zac67
Yes, exactly. I am interested in the mechanics of copying  :-)

I know longtracks can't be written on standard Amy hardware (you'll need a cyclone and some luck for that!). I'm interested in creating something that would copy MFM protected disks... and from your advice that sounds like quite an artform  ;-)

[msh5150]

@MarkAshley

>"So surely if the exact same pattern of 1s and 0s is duplicated on another disk"...

But that's the tricky part.  Let's take a typical Amiga disk protection - the "longtrack".

A longtrack has slightly more data on the disk than can be written by a normal Amiga drive. This is achieved by using some special hardware copier (or a modded Amiga). It works by slowing the drive spin-speed down a little (15% or so)- this has the effect of making the disk slightly higher 'density' if you like.  This disk track will now contain more data than a standard track. Hence why it's called a 'longtrack'.

Now, the Amiga disk controller is quite good natured and will read this longtrack no problem. But as the Amiga cannot control the disk spin speed it is unable to WRITE an identical copy.

The protection code on the disk will be able to tell this isn't the original track - ie. GAME OVER  :-)

That is why the game needs to be cracked - to stop the game realising it's not an original disk  :-D

[msh5150]

Hardware copiers didn't produce 'perfect' copies.  They might have been good enough to fool the protection code, but the aren't usually identical.

CAPS (SPS) have an artical about it here:
http://www.softpres.org/?id=glossary:hardware_copier

It appears that they copy the data in a more analog way and so degrade with each generation.