MAMEWorld Forums - EmuChat - Re: Can it beat t7z though?

> > Also CHDs is what consumes the most out of everything these days. That would
> probably
> > be better served if CHDs could inherit from each other like VDI/VHD files do with
> x86
> > virtual machines.
>
> CHDs *can* inherit from each other. The Virtual PC VHD file and MAME CHD were
> invented by the same person, after all (note the similar acronyms). It's just not
> worthwhile savings for the arcade games we support at the present time.
>
> I do think once we get serious about software lists for e.g. Windows 95 that we'll
> want a base parent Win95 install and various games and apps will be child CHDs that
> overlay an install of that item on top of the base OS install.

Cool I suspected as much.

I fiddled with it just to see what would happen. The docs were not totally clear how this worked

I used gauntlet legends
chdman -o test.chd -i gauntl12.chd -op gauntleg.chd

~1gig to ~7 meg. Not bad... The cost would probably be semi heavy during mid emulation though.

I then picked a couple of the CD games at random. It was ~2k saved and 2meg as suspected (basically not worth the trouble). If I remember correctly ISOs just linearly drops the data one after another. So if say a file was patched and added/removed enough it would have a different size and move the sectors around after that point. This is the case I was thinking about. But now that I tried and put a bit more thought into it probably would not work very well.

It probably would only work decently on hard drives where there was some sort of update done in place. It would probably need to be from the same machine to have a shot at being kinda close. You might get lucky with two different machines and it smashes up nicely but that would be rare. It might also work if the manufactures had a golden image and updated it in place and did not recreate the whole thing. I suspect the atari/midway games probably would work decently this way.

Yeah the win95 thing will be interesting. As 'just works' is appealing vs 'install windows and then your software'. Both ways have very valid reasons for being done.