Long story short: I have a big PC game collection from golden era (1995 - 2010) - digital ISOs and BINs and a limited space to preserve them. I dont trust clouds in any form, so I prefer old school external HDDs for store. For me 7Zip is a good way to archive them and save some space, but recently ive found out that if you convert a BIN or an ISO file to ECM and then you archive it with 7Zip (ultra compression), the final compression file size will be in most cases almost at a half compared to original non ECM file.

Example:

Original Bin file (rld-cl1.bin) - 672MB

Original Bin file zipped with 7zip on ultra compression (rld-cl1.7z) - 268MB

Original Bin file converted to ECM (rld-cl1.bin.ecm) - 586MB

Original Bin file converted to ECM zipped with 7zip on ultra compression (rld-cl1.bin.7z) - 195MB

So there is a difference of 73MB in this case.

Does this method is good? You can damage the BINs in any way if you ECM them, ZIP them, unzip them and UnECM them back to BIN? I noticed in properties of an UnECM(ed) BIN file that the BIN no longer have Last Modified Original Date - in this case was year 2005.

There are other different methods to save space? I dont care much about loading time from archiving/extracting. I just want to be sure that all the files remain untouched in this process. Thanks

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[–] [email protected] 7 points 2 years ago* (last edited 2 years ago) (2 children)

Well you're compressing it twice. Generally it's bad practice to compress a file twice, but it does happen a lot. For example a single zip file that packages several compressed archives. Personally I would live with the small amount of space it requires to avoid using two tools instead of one. Other than that it doesn't hurt anything and and there's no inherent risk of file corruption.

[–] [email protected] 3 points 2 years ago

I read somewhere that ECM compresses by removing the error-correction sectors from an ISO file.

It's already proven that discs can technically work without them. Dreamcast GD-ROMs are basically the practical application of this concept, with the goal of expanding CD-ROM storage from 700MB to 1GB.

That's why the size reduction is cumulative if the user apply ECM and then 7zip compression afterwards. That's because ECM is actually a trimming method rather than an actual compression scheme in the traditional sense.

[–] [email protected] 1 points 2 years ago

I had only heard that there wasn't much merit to multiple layers of compression as there is only so much compression that can be done.

One similar solution to OP here is tarballs.