-m (Set compression Method) switch

Specifies the compression method.

Syntax

-m<method_parameters>

The format for this switch depends on the archive type.

• Zip
• GZip
• BZip2
• 7z
• XZ

Zip

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.

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

BZip2

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

Sets level of compression

Level	NumPasses	Description
5	1	Default compression method.
7	2	Maximum compression method.
9	7	Ultra compression method.

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

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

Sets level of compression

Level	Method	Dictionary	FastBytes	MatchFinder	Filter	Description
0	Copy					No compression.
1	LZMA	64 KB	32	HC4	BCJ	Fastest compressing
3	LZMA	1 MB	32	HC4	BCJ	Fast compressing
5	LZMA	16 MB	32	BT4	BCJ	Normal compressing
7	LZMA	32 MB	64	BT4	BCJ	Maximum compressing
9	LZMA	64 MB	64	BT4	BCJ2	Ultra compressing

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]

Enables or disables compression filters for executable files: dll, exe, ocx, sfx, sys. It uses BCJ2 filter in Ultra mode and BCJ filter in other modes. The default mode is f=on.

hc=[off | on]

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

he=[off | on]

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

{N}

Sets order of methods. It is used also to associate parameters with methods. Numbers must begin from 0. Methods that have smaller numbers will be used before others.

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 LZMA.

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] switch for details).

Parameter	Default	Description
a=[0|1]	1	Sets compressing mode
d={Size}[b|k|m]	24	Sets Dictionary size
mf={MF_ID}	bt4	Sets Match Finder
fb={N}	32	Sets number of Fast Bytes
mc={N}	32	Sets 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]

Sets Dictionary size for LZMA. You must specify the size in bytes, kilobytes, or megabytes. The maximum value for dictionary size is 1 GB = 2^30 bytes. 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], 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	Memory	Description
bt2	d*9.5 + 4 MB	Binary Tree with 2 bytes hashing.
bt3	d*11.5 + 4 MB	Binary Tree with 3 bytes hashing.
bt4	d*11.5 + 4 MB	Binary Tree with 4 bytes hashing.
hc4	d*7.5 + 4 MB	Hash Chain with 4 bytes hashing.

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:

• Better compression ratio for data than can't be compressed. LZMA2 can store such blocks of data in uncompressed form. Also it decompresses such data faster.
• Better multithreading support. If you compress big file, LZMA2 can split that file to chunks and compress these chunks in multiple threads.

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

If you don't specify ChunkSize, LZMA2 sets it to 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]	24	Sets size of used memory for PPMd.
o={Size}	6	Sets model order for PPMd.

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 2GB = 2^31 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 [2,32]. 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:

• s0: main stream. It requires further compression.
• s1: stream for converted CALL values. It requires further compression.
• s2: stream for converted JUMP values. It requires further compression.
• s3: service stream. It is already compressed.

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.

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

Examples

7z a -tzip archive.zip *.jpg -mx0

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

7z a -t7z archive.7z *.exe *.dll -m0=BCJ -m1=LZMA:d=21 -ms -mmt

adds *.exe and *.dll files to solid archive archive.7z using LZMA method with 2 MB dictionary and BCJ converter. Compression will use multithreading optimization.

7z a -t7z archive.7z *.exe *.dll -m0=BCJ2 -m1=LZMA:d23 -m2=LZMA:d19 -m3=LZMA:d19 
     -mb0:1 -mb0s1:2 -mb0s2:3

adds *.exe and *.dll files to archive archive.7z using BCJ2 converter, LZMA with 8 MB dictionary for main output stream (s0), and LZMA with 512 KB dictionary for s1 and s2 output streams of BCJ2.

7z a -t7z archive.7z *.txt -m0=PPMd

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

Commands that can be used with this switch

a (Add), d (Delete), u (Update),

See also

Switches: -t (set Type of archive),