7-Zip Method Codes

When you open a 7-Zip archive in a UI or with 7z l -slt, you’ll see a “Method” field (e.g., LZMA2:24) indicating which method was used to compress the files in the archive.

Below are some of the most common ones and what they mean. While they do not uniquely identify all settings that were used, they are useful for trying to determine how the data was originally compressed.

General Information

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The most basic and universal method is simply having no compression at all.

Otherwise, the method is typically composed of the name of the compression method and a sequence of parameters specific to it, {MethodId}:{ParamName}{Value}:....

Often, the only parameter listed is the dictionary size, which is encoded as a power-of-two number of bytes when possible.

• For example, LZMA2:24 uses the LZMA2 compression method with a dictionary size of \(2^{24} \text{ bytes} = 2^4 \cdot 2^{20} \text{ bytes} = 16 \text{ MiB}\).
• If the size is not a perfect power of two, the number of MiB is used instead with an m suffix, e.g., LZMA2:48m means 48 MiB.

Methods can also be prefixed by the compression filters used in a similar format, (e.g., Delta LZMA2:24 or Delta:4 LZMA2:24) or suffixed with other method-specific parameters (e.g., LZMA2:24:lc1:lp2).

The possible compression filters are Delta, BCJ, BCJ2, ARM64, ARMT, ARM, PPC, SPARC, IA64, Swap2 and Swap4.

LZMA and LZMA2

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For the LZMA compression methods, the parameter is usually just the dictionary size. LZMA and LZMA2 share the same format.

PPMd

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For PPMd, the parameters typically show both the word size and dictionary size. Examples are shown below.

BZip2, Deflate, and Deflate64

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These compression methods often do not have any extra components unless filters or specific parameters were passed.

See also and references

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Please also refer to the documentation available at the main 7-Zip website and some basic details over on their Wikipedia page.