7-Zip manual: -m (Set compression Method) switch

-m (Set compression Method) switch

-m (Set compression Method) switch

Specifies the compression method.

Syntax

-m<method_parameters>

The format for this switch depends on the archive type.

-m switch also can specify hash method for h (Hash) command,

Notes: "Default value" in switches descriptions means the value that will be used if switch is not specified.

It's allowed to use reduced forms for boolean switches: sw+ or sw instead sw=on, and sw- instead of sw=off.

Zip

Parameter Default Description
x=[0 | 1 | 3 | 5 | 7 | 9 ] 5 Sets level of compression.
m={MethodID} Deflate Sets a method: Copy, Deflate, Deflate64, BZip2, LZMA, PPMd.
fb={NumFastBytes} 32 Sets number of Fast Bytes for Deflate encoder.
pass={NumPasses} 1 Sets number of Passes for Deflate encoder.
d={Size}[b|k|m] 900000 Sets Dictionary size for BZip2
mem={Size}[b|k|m] 24 Sets size of used memory for PPMd.
o={Size} 8 Sets model order for PPMd.
mt=[off | on | {N}] on Sets multithreading mode.
em={EncryptionMethodID} ZipCrypto Sets a encryption method: ZipCrypto, AES128, AES192, AES256
tc=[off | on] on Stores NTFS timestamps for files: Modification time, Creation time, Last access time.
cl=[off | on] off 7-Zip always uses local code page for file names.
cu=[off | on] off 7-Zip uses UTF-8 for file names that contain non-ASCII symbols.
cp={CodePage} off Sets code page

By default (if cl and cu switches are not specified), 7-Zip uses UTF-8 encoding only for file names that contain symbols unsupported by local code page.

x=[0 | 1 | 3 | 5 | 7 | 9 ]

Sets level of compression. x=0 means Copy mode (no compression).

Deflate / Deflate64 settings:

Level NumFastBytes NumPasses Description
1 32 1 Fastest
3 Fast
5 Normal
7 64 3 Maximum
9 128 10 Ultra

x=1 and x=3 with Deflate method set fast mode for compression.

BZip2 settings:

Level Dictionary NumPasses Description
1 100000 1 Fastest
3 500000 Fast
5 900000 Normal
7 2 Maximum
9 7 Ultra
fb={NumFastBytes}

Sets the number of fast bytes for the Deflate/Deflate64 encoder. It can be in the range from 3 to 258 (257 for Deflate64). Usually, a big number gives a little bit better compression ratio and a slower compression process. A large fast bytes parameter can significantly increase the compression ratio for files which contain long identical sequences of bytes.

pass={NumPasses}

Sets number of passes for Deflate encoder. It can be in the range from 1 to 15 for Deflate and from 1 to 10 for BZip2. Usually, a big number gives a little bit better compression ratio and a slower compression process.

d={Size}[b|k|m]

Sets the Dictionary size for BZip2. You must specify the size in bytes, kilobytes, or megabytes. The maximum value for the Dictionary size is 900000b. If you do not specify any symbol from set [b|k|m], dictionary size will be calculated as DictionarySize = 2^Size bytes.

mem={Size}[b|k|m]

Sets the size of memory used for PPMd. You must specify the size in bytes, kilobytes, or megabytes. The maximum value is 256 MB = 2^28 bytes. The default value is 24 (16MB). If you do not specify any symbol from the set [b|k|m], the memory size will be calculated as (2^Size) bytes. PPMd uses the same amount of memory for compression and decompression.

o={Size}

Sets the model order for PPMd. The size must be in the range [2,16]. The default value is 8.

mt=[off | on | {N}]

Sets multithread mode. If you have a multiprocessor or multicore system, you can get a speed increase with this switch. This option affects only compression (with any method) and decompression of BZip2 streams. Each thread in the multithread mode uses 32 MB of RAM for buffering. If you specify {N}, 7-Zip tries to use N threads.

GZip

GZip uses the same parameters as Zip, but GZip compresses only with Deflate method. So GZip supports only the following parameters: x, fb, pass.

BZip2

Parameter Default Description
x=[1 | 3 | 5 | 7 | 9 ] 5 Sets level of compression.
pass={NumPasses} 1 Sets number of Passes for Bzip2 encoder.
d={Size}[b|k|m] 900000 Sets Dictionary size for BZip2
mt=[off | on | {N}] on Sets multithreading mode.
x=[1 | 3 | 5 | 7 | 9 ]

Sets level of compression

Level Dictionary NumPasses Description
1 100000 1 Fastest
3 500000 Fast
5 900000 Normal
7 2 Maximum
9 7 Ultra
d={Size}[b|k|m]

Sets the Dictionary size for BZip2. You must specify the size in bytes, kilobytes, or megabytes. The maximum value for the Dictionary size is 900000b. If you do not specify any symbol from set [b|k|m], dictionary size will be calculated as DictionarySize = 2^Size bytes.

pass={NumPasses}

Sets the number of passes. It can be in the range from 1 to 10. The default value is 1 for normal mode, 2 for maximum mode and 7 for ultra mode. A bigger number can give a little bit better compression ratio and a slower compression process.

mt=[off | on | {N}]

Sets multithread mode. If you have a multiprocessor or multicore system, you can get a speed increase with this switch. If you specify {N}, for example mt=4, 7-Zip tries to use 4 threads.

7z

Parameter Default Description
x=[0 | 1 | 3 | 5 | 7 | 9 ] 5 Sets level of compression.
yx=[0 | 1 | 3 | 5 | 7 | 9 ] 5 Sets level of file analysis.
s=[off | on | [e] [{N}f] [{N}b | {N}k | {N}m | {N}g] on Sets solid mode.
qs=[off | on] off Sort files by type in solid archives.
f=[off | on | FilterID] on Enables or disables filters. FilterID: Delta:{N}, BCJ, BCJ2, ARM, ARMT, IA64, PPC, SPARC.
hc=[off | on] on Enables or disables archive header compressing.
he=[off | on] off Enables or disables archive header encryption.
b{C1}[s{S1}]:{C2}[s{S2}] Sets binding between coders.
{N}={MethodID}[:param1][:param2][..] LZMA2 Sets a method: LZMA, LZMA2, PPMd, BZip2, Deflate, Delta, BCJ, BCJ2, Copy.
mt=[off | on | {N}] on Sets multithreading mode.
mtf=[off | on] on Set multithreading mode for filters.
tm=[off | on] on Stores last Modified timestamps for files.
tc=[off | on] off Stores Creation timestamps for files.
ta=[off | on] off Stores last Access timestamps for files.
x=[0 | 1 | 3 | 5 | 7 | 9 ]

Sets level of compression

Level Method Dictionary FastBytes MatchFinder Filter Description
0 Copy No compression.
1 LZMA2 64 KB 32 HC4 BCJ Fastest compressing
3 LZMA2 1 MB 32 HC4 BCJ Fast compressing
5 LZMA2 16 MB 32 BT4 BCJ Normal compressing
7 LZMA2 32 MB 64 BT4 BCJ Maximum compressing
9 LZMA2 64 MB 64 BT4 BCJ2Ultra compressing

Note: "x" works as "x=9".

yx=[0 | 1 | 3 | 5 | 7 | 9 ]

Sets level of file analysis

Level Description
0 No analysis.
1 or more WAV file analysis (for Delta filter).
7 or more EXE file analysis (for Executable filters).
9 or more analysis of all files (Delta and executable filters).

Default level is 5: "yx=5".

"yx" works as "yx=9".

If the level of analysis is smaller than 9, 7-Zip analyses only files that have some file name extensions: EXE, DLL, WAV. 7-Zip reads small data block at the beginning of file and tries to parse the header. It supports only some formats: WAV, PE, ELF, Mach-O. Then it can select filter that can increase compression ratio for that file.

By default 7-Zip uses x86 filters (BCJ or BCJ2) for PE files (EXE, DLL). 7-Zip doesn't use analysis in default (yx=5) mode. If (yx=7), then analysis is used for PE files, and it can increase compression ratio for files for non-x86 platforms like ARM.

s=[off | on | [e] [{N}f] [{N}b | {N}k | {N}m | {N}g)]

Enables or disables solid mode. The default mode is s=on. In solid mode, files are grouped together. Usually, compressing in solid mode improves the compression ratio.

e Use a separate solid block for each new file extension
{N}f Set the limit for number of files in one solid block
{N}b | {N}k | {N}m | {N}g Set a limit for the total size of a solid block in bytes

These are the default limits for the solid block size:

Compression Level Solid block size
Store 0 B
Fastest 16 MB
Fast 128 MB
Normal 2 GB
Maximum 4 GB
Ultra 4 GB

Limitation of the solid block size usually decreases compression ratio but gives the following advantages:

  • Decreases losses in case of future archive damage.
  • Decreases extraction time of a group of files (or just one file), so long as the group doesn't contain the entire archive.

The updating of solid .7z archives can be slow, since it can require some recompression.

Example:

        s=100f10m

set solid mode with 100 files & 10 MB limits per one solid block.

f=[off | on | FilterID]

Enables or disables compression filters. The default mode is f=on, when 7-zip uses filter only for executable files: dll, exe, ocx, sfx, sys. It uses BCJ2 filter in Ultra mode and BCJ filter in other modes. If f=FilterID if specified, 7-zip uses specified filter for all files. FilterID can be: Delta:{N}, BCJ, BCJ2, ARM, ARMT, IA64, PPC, SPARC.

hc=[off | on]

Enables or disables archive header compressing. The default mode is hc=on. If archive header compressing is enabled, the archive header will be compressed with LZMA method.

he=[off | on]

Enables or disables archive header encryption. The default mode is he=off.

b{C1}[s{S1}]:{C2}[s{S2}]

Binds output stream S1 in coder C1 with input stream S2 in coder C2. If stream number is not specified, stream with number 0 will be used.

Usally coder has one input stream and one output stream. In 7z some coders can have multiple input and output streams.

For example, BCJ2 encoder has one input stream and four output streams.

mt=[off | on | {N}]

Sets multithread mode. If you have a multiprocessor or multicore system, you can get a increase with this switch. 7-Zip supports multithread mode only for LZMA / LZMA2 compression and BZip2 compression / decompression. If you specify {N}, for example mt=4, 7-Zip tries to use 4 threads. LZMA compression uses only 2 threads.

{N}={MethodID}[:param1][:param2] ... [:paramN]

Sets compression method. You can use any number of methods. The default method is LZMA2.

{N} sets the index number of method in methods chain. Numbers must begin from 0. Methods that have smaller numbers will be used before others.

Parameters must be in one of the following forms:

  • {ParamName}={ParamValue}.
  • {ParamName}{ParamValue}, if {ParamValue} is number and {ParamName} doesn't contain numbers.

Supported methods:

MethodID Description
LZMA LZ-based algorithm
LZMA2 LZMA-based algorithm
PPMd Dmitry Shkarin's PPMdH with small changes
BZip2 BWT algorithm
Deflate LZ+Huffman
Copy No compression

Supported filters:

MethodID Description
Delta Delta filter
BCJ converter for x86 executables
BCJ2 converter for x86 executables (version 2)
ARM converter for ARM (little endian) executables
ARMT converter for ARM Thumb (little endian) executables
IA64 converter for IA-64 executables
PPC converter for PowerPC (big endian) executables
SPARC converter for SPARC executables

Filters increase the compression ratio for some types of files. Filters must be used with one of the compression method (for example, BCJ + LZMA).

LZMA

LZMA is an algorithm based on Lempel-Ziv algorithm. It provides very fast decompression (about 10-20 times faster than compression). Memory requirements for compression and decompression also are different (see d={Size}[b|k|m|g] switch for details).

Parameter Default Description
a=[0|1] 1 Sets compressing mode
d={Size}[b|k|m|g] 24 Sets Dictionary size
mf={MF_ID} bt4 Sets Match Finder
fb={N} 32 Sets number of Fast Bytes
mc={N} 32Sets Number of Cycles for Match Finder
lc={N} 3 Sets number of Literal Context bits - [0, 8]
lp={N} 0 Sets number of Literal Pos bits - [0, 4]
pb={N} 2 Set number of Pos Bits - [0, 4]
a=[0|1]

Sets compression mode: 0 = fast, 1 = normal. Default value is 1.

d={Size}[b|k|m|g]

Sets Dictionary size for LZMA. You must specify the size in bytes, kilobytes, or megabytes. The maximum value for dictionary size is 1536 MB, but 32-bit version of 7-Zip allows to specify up to 128 MB dictionary. Default values for LZMA are 24 (16 MB) in normal mode, 25 (32 MB) in maximum mode (-mx=7) and 26 (64 MB) in ultra mode (-mx=9). If you do not specify any symbol from the set [b|k|m|g], the dictionary size will be calculated as DictionarySize = 2^Size bytes. For decompressing a file compressed by LZMA method with dictionary size N, you need about N bytes of memory (RAM) available.

mf={MF_ID}

Sets Match Finder for LZMA. Default method is bt4. Algorithms from hc* group don't provide a good compression ratio, but they often work pretty fast in combination with fast mode (a=0). Memory requirements depend on dictionary size (parameter "d" in table below).

MF_ID Dictionary Memory Usage Description
bt2 9.5 * d + 4 MB Binary Tree 2 bytes hashing
bt3 11.5 * d 3 bytes hashing
bt4 64 KB ... 48 MB 11.5 * d 4 bytes hashing
64 MB ... 1024 MB 10.5 * d
hc4 64 KB ... 48 MB 7.5 * d Hash Chain
64 MB ... 1024 MB 6.5 * d

Note: Your operation system also needs some amount of physical memory for internal purposes. So keep at least 32MB of physical memory unused.

fb={N}

Sets number of fast bytes for LZMA. It can be in the range from 5 to 273. The default value is 32 for normal mode and 64 for maximum and ultra modes. Usually, a big number gives a little bit better compression ratio and slower compression process.

mc={N}

Sets number of cycles (passes) for match finder. It can be in range from 0 to 1000000000. Default value is (16 + number_of_fast_bytes / 2) for BT* match finders and (8 + number_of_fast_bytes / 4) for HC4 match finder. If you specify mc=0, LZMA will use default value. Usually, a big number gives a little bit better compression ratio and slower compression process. For example, mf=HC4 and mc=10000 can provide almost the same compression ratio as mf=BT4.

lc={N}

Sets the number of literal context bits (high bits of previous literal). It can be in range from 0 to 8. Default value is 3. Sometimes lc=4 gives gain for big files.

lp={N}

Sets the number of literal pos bits (low bits of current position for literals). It can be in the range from 0 to 4. The default value is 0. The lp switch is intended for periodical data when the period is equal to 2^value (where lp=value). For example, for 32-bit (4 bytes) periodical data you can use lp=2. Often it's better to set lc=0, if you change lp switch.

pb={N}

Sets the number of pos bits (low bits of current position). It can be in the range from 0 to 4. The default value is 2. The pb switch is intended for periodical data when the period is equal 2^value (where lp=value).

LZMA2

LZMA2 is modified version of LZMA. it provides the following advantages over LZMA:

Parameter Default Description
c={Size}[b|k|m|g] dictSize * 4 Sets Chunk size

If you don't specify ChunkSize, LZMA2 sets it to max(DictionarySize, min(256M, max(1M, DictionarySize * 4))).

LZMA2 also supports all LZMA parameters, but lp+lc cannot be larger than 4.

LZMA2 uses: 1 thread for each chunk in x1 and x3 modes; and 2 threads for each chunk in x5, x7 and x9 modes. If LZMA2 is set to use only such number of threads required for one chunk, it doesn't split stream to chunks. So you can get different compression ratio for different number of threads. You can get the best compression ratio, when you use 1 or 2 threads.

PPMd

PPMd is a PPM-based algorithm. This algorithm is mostly based on Dmitry Shkarin's PPMdH source code. PPMd provides very good compression ratio for plain text files. There is no difference between compression speed and decompression speed. Memory requirements for compression and decompression also are the same.

Parameter Default Description
mem={Size}[b|k|m|g] 24 Sets size of used memory for PPMd.
o={Size} 6 Sets model order for PPMd.
mem={Size}[b|k|m|g]

Sets the size of memory used for PPMd. You must specify the size in bytes, kilobytes, or megabytes. The maximum value is 2GB = 2^31 bytes. The default value is 24 (16MB). If you do not specify any symbol from the set [b|k|m|g], the memory size will be calculated as (2^Size) bytes. PPMd uses the same amount of memory for compression and decompression.

o={Size}

Sets the model order for PPMd. The size must be in the range [2,32]. The default value is 6.

BCJ2

BCJ2 is a Branch converter for 32-bit x86 executables (version 2). It converts some branch instructions for increasing further compression.

A BCJ2 encoder has one input stream and four output streams:

If LZMA is used, the size of the dictionary for streams s1 and s2 can be much smaller (512 KB is enough for most cases) than the dictionary size for stream s0.

Parameters:

d={Size}[b|k|m|g]

Sets section size for BCJ2 filter. Default section size is 64 MB. If you do not specify any symbol from the set [b|k|m|g], the section size will be calculated as SectionSize = 2^Size bytes. This parameter doesn't affect memory consumption. Compression ratio is better, if the section size is equal or slightly larger than size of largest execution section in file. Example: f=BCJ2:d9M, if largest executable section in files is smaller than 9 MB.

Delta

It's possible to set delta offset in bytes. For example, to compress 16-bit stereo WAV files, you can set "0=Delta:4". Default delta offset is 1.

XZ

XZ supports only LZMA2 codec now. The switches are similar to switches for 7z format.

Parameter Default Description
x=[0 | 1 | 3 | 5 | 7 | 9 ] 5 Sets level of compression
f=FilterID Sets compression filter. FilterID: Delta:{N}, BCJ, ARM, ARMT, IA64, PPC, SPARC
{N}={MethodID}[:param1][:param2][..] LZMA2 Sets compression method: LZMA2:[param1]:[param2]:[...]
mt=[off | on | {N}] on Sets multithreading mode

WIM

Parameter Default Description
im={ImageNumber} Sets image number.
is=[off | on] off Show image number in paths.

If image number is specified, 7-Zip works only with that image inside WIM archive. Other images will be not changed. By default 7-Zip doesn't show image number, if there is only one image in WIM archive, or if image number is specified. But if the switch "is" specified, 7-Zip shows image number.

Examples

7z a archive.zip *.jpg -mx0

adds *.jpg files to archive.zip archive without compression.

7z a archive.7z *.exe *.dll -m0=BCJ -m1=LZMA:d=21

adds *.exe and *.dll files to solid archive archive.7z using LZMA method with 2 MB dictionary and BCJ filter.

7z a archive.7z a.tar -mf=BCJ2 -mx

adds a.tar files to archive archive.7z using BCJ2 filter.

7z a archive.7z *.wav -mf=Delta:4

adds *.wav files to archive archive.7z using Delta:4 filter.

7z a a.7z *.exe *.dll -m0=BCJ2 -m1=LZMA:d25 -m2=LZMA:d19 -m3=LZMA:d19 -mb0:1 -mb0s1:2 -mb0s2:3

adds *.exe and *.dll files to archive a.7z using BCJ2 filter, LZMA with 32 MB dictionary for main output stream (s0), and LZMA with 512 KB dictionary for s1 and s2 output streams of BCJ2.

7z a archive.7z *.txt -m0=PPMd

adds *.txt files to archive archive.7z using PPMd method.

7z a a.tar.xz a.tar -mf=bcj -mx

adds a.tar files to archive a.tar.xz using BCJ filter.

Commands that can be used with this switch

a (Add), h (Hash), d (Delete), rn (Rename), u (Update)

See also

Switches: -t (set Type of archive),

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