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We have an old application that requires zip files to be "legacy" format. I would really love to get rid of the adware ridden WinZip and use 7zip. However, I don't know which compression options and such equal out to "legacy".

How to do it?

For reference the compression methods I have to choose from are

  1. Deflate
  2. Deflate64
  3. BZip2
  4. LZMA
  5. PPMd

Or does which compression method I use even matter? Would it all end up going in as a "legacy" zip file anyway?

Earlz
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1 Answers1

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Legacy zip compression is akin to the Deflate method in 7-zip, and will offer the most compatibility between different compression software.

From the Winzip KB:

.Zip Legacy compression (maximum compatibility):

The Legacy (Zip 2.0) compression option uses a traditional data compression algorithm, known as deflate, that is supported by all versions of WinZip and virtually all other Zip file utilities. The deflate method is generally considered to be a good all-purpose compression algorithm for most types of files. .Zip: Legacy compression is your best choice when your mail recipient's Zip utility is unknown or known to use older technology. WinZip and WinZip Courier actually use the highest available compression setting for the deflate method or maximum deflate. This way you get the smallest, compatible Zip files possible.

John T
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  • If the archive extension is .ZIP then specifying the Deflate method is sufficient to get legacy compression. However if the extension is not .ZIP, it seems the command-line 7z.exe defaults _Type of archive_ to -t7z and so -tzip must be specified instead (or in addition). – noam Oct 09 '18 at 12:13
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    "If -t{archive_type} switch is not specified, 7-Zip uses extension of archive filename to detect the type of archive. If you create new archive, -t{archive_type} switch is not specified and there is no extension of archive, 7-Zip will create .7z archive." https://sevenzip.osdn.jp/chm/cmdline/switches/type.htm – noam Oct 09 '18 at 13:36