What does the "m" mean in "LZMA2:192m" from 7z t?

[HyperBear]

When creating an archive with high compression settings ( 7z a -md=1024m -mfb=128 -ms=on -mx=9 ) and then running 7z t, one line from the output is:

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Method = LZMA2:192m

For an archive created using file-roller or the default 7z settings (no additional parameters):

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Method = LZMA2:24

What does the "m" from "192m" mean?

I am assuming the number means dictionary size in megabytes, and it is not "1024m" because the archive only contains 170 MB of uncompressed data. However, if it means "megabytes", how come "LZMA2:24" has no "m" after it?

[stevengarland]

https://superuser.com/questions/665113/ ... witch-mean

[karlchen]

Hello, HyperBear.

Your understanding of Method = LZMA2:192m is correct: dictionary size of 192 MiB. Reduced from 1024m given on the commandline to 192m, because dictionary size much larger than data size does not improve the compression ratio.

Method = LZMA2:24 means dictionary size: 2^24. If no size is suffixed to the given number it is interpreted as a power of two: 24 => 2^24.
Cf. LZMA2:24 (or 192k), please.

Karl