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I am sorry if I sound wired!.

After reading about .zip and .zip64 in the wiki, I realized that one of the major differences is about the size limit.

Here is my options:

SL # Raw file File size compressed extension zip archive required to unzip
1 abc.doc 3.5 GB .zip v 2.0
2 def.doc 4.5 GB .zip v 4.5

FYI, for both files, the file extension is .zip, although #2 is using zip64.

My question is, shouldn't it (# 2) has .zip64 extension since it's a zip64 file?

Or is it's lack of my understanding that zip64 compressed files also have .zip extension?

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  • 2
    I'd take a guess that the distinction is internal. I have [& have had over many many years] zip files on many different platforms that are hundreds of gigabytes & have never ever seen a .zip64 extension. [I'll leave the actual answer to someone who can maybe find a citation for that]
    – Tetsujin
    Sep 1, 2021 at 15:14
  • @Tetsujin Thank you for your comment. I have literally the same feeling as you have. However, after reading this particular section I feel .zip64 should be an extension as well. Correct me if I am wrong.
    – tisuchi
    Sep 1, 2021 at 15:19

1 Answer 1

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If people cared to make that distinction then they can, and there is nothing really stopping them. It would certainly help with ancient software that doesn't understand Zip64 format files, but that software should be quite rare these days. It boils down to whether enough people actually care enough about it, which likely isn't that many people when simply using a zip tool updated since 2001 should be enough.

From The Zip version history

  • 2.0: (1993) File entries can be compressed with DEFLATE and use traditional PKWARE encryption (ZipCrypto).
  • 2.1: (1996) Deflate64 compression
  • 4.5: (2001) Documented 64-bit zip format.
  • 4.6: (2001) BZIP2 compression (not published online until the publication of APPNOTE 5.2)
  • 5.0: (2002) SES: DES, Triple DES, RC2, RC4 supported for encryption (not published online until the publication of APPNOTE 5.2)

"Old" zip and zip64 are still both part of the Zip Specification.

File extensions are far more convention and agreements between people than they are hard identifiers of documents for computers. Many formats get updated over the years but still retain the same file extension.

A person needs to know "a zip tool will open this". The computer will look at the actual data within the file to work out exactly what kind of file it is dealing with and how to open it.

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  • Ahh… that may be why I've never seen it. I think in 2001 I was still using Stuffit, the "latest, greatest" replacement for CompactPro & also probably didn't have a HD bigger than 4GB ;))
    – Tetsujin
    Sep 1, 2021 at 15:35
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    I've added a bit more about the "human factor" to the end. The simple fact is that it is a distinction for humans and 99.9999% of the time we just don't need to care about the internals, only that our favourite tool "just works".
    – Mokubai
    Sep 1, 2021 at 15:37
  • @Mokubai Thank you for your explanation. If I sum up my understanding from your comment is both zip and zip64 are under the zip specification, therefore by default zip64 compressed file also has .zip extension. However, depending on the requirements, I can able to change .zip64 if I wish. ???
    – tisuchi
    Sep 1, 2021 at 15:41
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    Yes, they are both technically zip files under the specification and so share the extension. One is technically just an update to the older version and not really considered "unique" enough to warrant a new extension. You are free to use whatever extension you wish, and no one can really stop you, but you may end up needing to manually set up file associations and people who are used to them just being zip files may look at you oddly before renaming them back. There's no real reason to name them zip64...
    – Mokubai
    Sep 1, 2021 at 15:46
  • @Mokubai makes sense. Thanks again for the clarification. :)
    – tisuchi
    Sep 1, 2021 at 16:06

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