Compress a large 4GB file to 1GB

I think you don't want to understand what is being said.
An ISO file contains a certain number of files.
It's these different files that are compressed. Some files are very easily compressible and others are not. So for certain types, you will achieve more than 50% compression and for others, less than 5%.

If you don't want to understand what others, including myself, are explaining to you, then program yourself a miracle software; maybe you'll win the Turing Award...

It depends on the content of the ISO. If it’s a game installer, for example, the data on the CD is likely already compressed. A second compression won’t give you more than 4 or 5%.
If you want to get 5% instead of 4, try 7-zip, but don’t expect miracles.

Hello again everyone...

There's no need to respond if you don't know the answer.

This question is here because it is possible to do this, I repeat:

I already have an ISO file that is compressed to 1.5 GB. Once decompressed, it results in a DVD ISO of 4.5 GB.

So if you don't know the real method, please don't respond, thank you (the pointless chatter tires me out, everyone would agree).
Also, if you think you know the method, try it out at home before suggesting it to me.

Thank you

(A good CCM is a well-thought-out and tested response before suggesting, then we wonder why we get lost in forums because of whom? Guess?)

Hello,

Could it be a Wii game ISO?
It is indeed possible to "scrub" certain games to compress them.
So it’s not WinRAR that does it directly, but software like WiiScrubber
--
Tøƒ

do you want this photo at the following link

http://pbjja.pagesperso-orange.fr/telechargement/ccm.JPG

if some people can do this, it is indeed possible to compress more

I have the compressed file at 1.5 GB which decompresses to 4.5 GB

we just need to find the software, there you go

I’m not asking for the impossible but I have the example so it is possible…

Good evening,

If we follow your reasoning, then the 4.5GB file compressed to 1.5GB should be compressible again by a factor of 3, bringing it down to 0.5GB. If that were the case, RAR would be garbage because it would have compressed by a factor of 3 when it could have done so by a factor of 9...
A file is compressible if it has a lot of repetitions (basically), and once compressed, there are no longer these repetitions that would allow for the same rate.
Moreover, a file compressed multiple times will eventually take up more space than the previous generation.
Eric

darkito simply answered my question, thank you again darkito.

Out of curiosity, if you can test both compressions (rar with and without WiiScrubber), could you please give us the sizes obtained?
eric

What type of file do you want to compress?

file is iso, archive type winrar

The 7zip format offers a better compression rate than its counterparts in .zip, .rar, and even .bz2.

It's possible, I agree, but only for certain files: bmp or pict images, wav or aiff sounds, text files that are not already compressed. What does your ISO contain?
I also advise you to take a look at this page: compression, which will allow you to learn a bit more about compression and understand that it's not just about reducing size.
Have you tried compressing your file to .7z using the software 7-zip?

this is already the beginning of an answer.