Question about diskimages in general

By Latok

msx guru (3686)

Latok's picture

21-12-2003, 00:28

Although I have many original games, it's no secret I also have some copied stuff Wink Many of these software titles have some kind of copy protection. Can be a bad sector, more than 80 tracks or an even more sophisticated copyright protection such as Microcabin has used.

All over the internet, I find Diskimages of this copyprotected software. My question is: Do they all work in emulators? Or has all this software been cracked in a way that the copyprotections aren't present anymore, so Diskimages from these software work in emulators?

I can imagine people just made diskimages from copyprotected software without really testing the diskimage. Are there a lot of diskimages which don't work at all in emulators?

I've only started with emulators just very recently, so erhm...my apologies if the questions sound 'very newbie' Tongue

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By mars2000you

Enlighted (5513)

mars2000you's picture

21-12-2003, 00:52

There are indeed bad disk images that doesn't work or only partially. Some people think that you must only copy the files that you see with "DIR" or "FILES", but some disks have also files "hidden" in sectors. It's the case for example of the Sunrise Magazine Disks. If you copy only the files that you see, you are missing a great part of the magazine !

The problem becomes more complex if you have a copy-protection. Some protections are so strong that you must "desactive" them, including the controls of the presence of the protection. It was the problem with the original FAC DEMO 5 : an extra sector and an very annoying copy-protection. Only openMSX can start the unmodified disk image !

In other cases, the protection must be first desactived to create the disk image, then must be reinserted to get a working disk image. It doesn't mean that all emulators can start such disk images. Only advanced emulators like openMSX and NLMSX, with a complete drive controller emulation, can start these disk images. That explains why some Sunrise games doesn't work on most of the fMSX clones !

By Latok

msx guru (3686)

Latok's picture

21-12-2003, 01:01

But do I understand you correctly that there ARE Diskmanagers who can make perfect images of copyprotected software? So they create e.g. virtual bad sectors and stuff?

By mth

Champion (484)

mth's picture

21-12-2003, 02:07

It is possible to make a special kind of disk image that can contain any kind of protection and some of these formats do exist, but as far as I know no MSX emulator supports them yet. It is not possible to include copy protections such as used by Sunrise in a standard 720K disk image.

The difference between NLMSX and openMSX compared to fMSX for disk emulation, is that fMSX puts invalid Z80 instructions on the disk ROM entry points and in that way the emulator can intercept the calls to the disk I/O routines and emulate them on a high level. NLMSX and openMSX instead emulate the hardware (FDC = Floppy Disk Controller) and are thus more accurate.

For example FastCopy copies only unprotected disks, but does so by accessing the FDC directly, which is also the reason why it can be so fast. FastCopy won't work on fMSX, but should work on NLMSX and openMSX. Formula, on the other hand, has some features to write non-standard sectors (different length, different number of sectors per track, CRC errors), for example to copy or create copy protections. Formula won't work correctly on any existing MSX emulator, because the standard DSK image format cannot handle non-standard sectors.