Are all ISOs created equal?

[kxkvi]

Earlier this evening, as I do often, I used ImgBurn to burn an ISO image to produce

a data DVD. As usual, the process was seamless and without incident.

 

Simply because I had a few extra minutes to devote to the project, I decided to

try an experiment. Using the same DVD that I had just burned, I used ImgBurn to

create an ISO image file from it, saving the output file to a different directory. When

the process finished, I checked the MD5 and SHA1 hahes of the newly created ISO.

I note that the hashes are different from the original ISO source file.

 

As such, I need to further my understanding of how ISO files are formatted and written.

What I need to comprehend is how two different ISO images are able to write identical

DVDs. I haven't really done a bitwise comparison of the data on two DVDs written

by the two files yet, but I have the ability to do this, and may add that to my list of things

to do tomorrow evening. In the meantime, if anyone can point me in the right direction,

I would be happy to include any information provided as an item for further study.

 

Enjoy the day.

 

Thomas

[LIGHTNING UK!]

What built the ISO in the first place?

 

If you burn to a DVD+R, the size could change as the drive will burn a multiple of 16 sectors.

[kxkvi]

What built the ISO in the first place?

 

I honestly don't know. The image was built by Microsoft, and as far as I know, I have no

way of determining how they generated the file.

 

If you burn to a DVD+R, the size could change as the drive will burn a multiple of 16 sectors.

 

That makes sense, since I did burn it to a DVD+R. Aside from that aspect, is there any

overhead, padding, or formatting that's applied when the image is built in ImgBurn?

 

Regards,

 

Thomas

[LIGHTNING UK!]

When ImgBurn 'builds' an ISO from scratch, it makes them a multiple of 16 (or 32) sectors so this type of thing isn't a problem.

 

When it 'reads' a disc and dumps the sectors to an ISO, it just reads the number of sectors the drive says are present - so no padding or whatever.

[kxkvi]

When ImgBurn 'builds' an ISO from scratch, it makes them a multiple of 16 (or 32) sectors so this type of thing isn't a problem.

 

Interesting. So it seems that in the end.. no, they aren't all created equal, even though their intent is the same. Apparently,

there is room to move around within the standard. This takes me back to the days when I saw heated debates in the forums

about "such-and-such's ISO app doesn't create a truly compliant image"

 

I just installed UltraISO on my machine. I'm going to give it a whirl this evening and see what I can do with it.

 

Regards,

 

Thomas

[kxkvi]

I just installed UltraISO on my machine. I'm going to give it a whirl this evening and see what I can do with it.

 

I built ISOs of the aforementioned DVD with both ImgBurn and UltraISO (with "skip bad sectors" and "volume filtering"

unticked). The files are identical in size. More importantly, the hashes match. I'm impressed!

 

UltraISO seems a useful tool, just as ImgBurn is.

 

Regards,

 

Thomas