compress ISO image

Discussion in 'Computing and Networks' started by electronis whiz, Aug 24, 2013.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    I have a lot of software I got that is saved on my external as ISO images. IO have 2 externals a primary, and backup. I'd like to compress the ISOs at least on the backup drive so have more room. I considered using 7 zip, but then remembered ISOs are supposedly already compressed so would there even be any point, and is this possible with out messing up ISO? I saw something on E how that said ISOs are images of whole disks so there is a lot of wasted space. I have a hard time believing that since not what I understood them as, and all of these ISOs are from downloads so I would think they would make it as small a file as possible.

    Any ideas on how well this would work or even if it would. :confused:
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
    Do you have something to lose by trying? You probably could have tried zipping an ISO in the time it took you to type the question.

    I think I tried zipping an ISO before with WINZIP, and it was the same size as before. But that was a few years ago, and my memory is worse than my grandmother's.
    panic mode likes this.
  3. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    I thought about, suppose make copy or got backup if messes up. I just kind of have doubts will work that well. probably use 7-zip since seems best compression program I've seen.
  4. Litch


    Jan 25, 2013
    An ISO is a disk image of the data that is on a CD/DVD.

    Note I said "image of the data" not "Image of the DVD" - thus if you have 300mb of data on a (normally 700mb) CD - the ISO will be 300mb in size.

    As for the "already compressed" issue - this is partially true since most data on CDs are for installing software - then most of the software's files are compressed, usually using a quick compression like cab (same as zip, different format).

    If you wanted to compress them further - depending on what's on them - then you could use WinRAR set to maximum compression, or BZIP2, also set to maximum - It would take a while and I'd say you'd get about 5-15% size reduction, assuming that the contents are CAB compressed. We can expand that to rationalise: For every 10 ISOs compressed, you can fit another on there for the same amount of space.

    The ISO would remain perfectly intact.

    If you should do it or not remains your choice, on an average PC (Dual 3.-GHz) compressing a full 700mb ISO using RAR on maximum compression would take about 2 minutes.
  5. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    Thanks for info. I kind of thought that is how ISOs worked, but other thing said bit by bit of whole disk. I never really thought about compression of the files already that much. but now that I think of it that seems right. I may give it a try on something and see if worth doing. Most of it is ISOs, but some of it is EXE, mac, Linux files think defiantly compress those if I can. unless already is like a tar ball.
  6. M15K

    New Member

    Sep 17, 2013
    If you are looking for a true long term storage you can try to go with something like RZIP or LRZIP. They use quite a bit larger dictionaries for compression than our usual fare. They are also based on known standard compression libraries like BZIP2 and LZMA.

    As you can imagine, it can take a while to pack.
  7. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    I would suggest 7-zip. So far I haven't found anything it won't handle. I expect you could use windows NTFS compression, or zip format, but I have fount 7-zip to work better than both. NTFS compression is not all that good, and you can't move to thumb drive unless you format that with NTFS which works, but I have had some issues with that.
    I tried it on a few files, and at least one ended up being larger after compressed even with 7-zip. I don't think you'll gain much compressing them actually since iso is already compressed somewhat. This also explains compression being larger. some reason you compress something compressed it does opposite.
  8. Ramussons

    Active Member

    May 3, 2013
    Compressing an ISO image is purely of academic interest.

  9. MikeLalonde

    New Member

    Dec 8, 2013
    Have you tried MagicISO? It supposedly will compress ISO files but with 1 TB drives at about $80 now it's not much of an issue to store the raw ISO files.

    Michael Lalonde <SNIP>
    Sudbury, Ontario
    Last edited by a moderator: Dec 8, 2013