-m (Set compression Method) switch

Specifies compression method.

Syntax

-m<method_parameters>

Format of this switch is depended from archive type.

Zip

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

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

pass={NumPasses}

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

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

Sets Dictionary size for BZip2. You must specify size in bytes, kilobytes, or megabytes. The maximum value for 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 multiprocessor system or Pentium 4 with hyperthreading, you can get speed increasing with this switch. This option affects only compressing with BZip2, Deflate and Deflate64 methods and decompressing of BZip2 streams. Each thread in 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 number of passes. It can be in range from 1 to 10. Default value is 1 for normal mode, 2 for maximum mode and 7 for ultra mode. Bigger number can give a little bit better compression ratio and slower compression process.

mt=[off | on | {N}]

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

7z

x=[0 | 1 | 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	4 MB	32	BT4	BCJ	Normal compressing
7	LZMA	16 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 compression ratio.

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

By default there is limitation for solid block size:

Compression Level	Solid block size
Store	0 B
Fastest	16 MB
Fast	128 MB
Normal	512 MB
Maximum	2 GB
Ultra	8 GB

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

• Decreases losses in case of future archive's damaging.
• Decreases extracting time of the group of files (it can be one file), if this group doesn't contain all files of archive.

Current version of 7-Zip doesn't support updating for solid archives, if it requires repacking solid blocks.

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.

hcf=[off | on]

Enables or disables full archive header compressing. The default mode is hcf=on. Archives created with hcf=on can be extracted by 7-Zip 2.30 beta 25 and more.

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. Method that have minor number 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 multiprocessor system or Pentium 4 with hyperthreading, you can get speed increasing with this switch. 7-Zip supports multithread mode only for LZMA compressing and BZip2 compressing / decompressing. If you specify {N}, for example mt=4, 7-Zip tries to use 4 threads. LZMA compressing 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	Algorithm based on LZ algorithm
PPMd	Dmitry Shkarin's PPMdH with small changes
BZip2	BWT algorithm
Deflate	LZ+Huffman
Copy	No compression

Supported filters:

MethodID	Description
BCJ	converter for x86 executables
BCJ2	converter for x86 executables (version 2)
BC_ARM	converter for ARM (little endian) executables
BC_ARMThumb	converter for ARM Thumb (little endian) executables
BC_IA64	converter for IA-64 executables
BC_PPC_B	converter for PowerPC (big endian) executables
BC_SPARC	converter for SPARC executables

Filters allow to increase 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 decompressing (about 10-20 times faster than compressing). Memory requirements for compressing and decompressing 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]	22	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 compressing mode: 0 = fast, 1 = normal. Default value is 1.

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

Sets Dictionary size for LZMA. You must specify size in bytes, kilobytes, or megabytes. The maximum value for dictionary size is 1 GB = 2^30 bytes. Default value for LZMA is 22 (4 MB) in normal mode, 24 (16 MB) in maiximum mode (-mx=7) and 26 (64 MB) in ultra mode (-mx=9). If you do not specify any symbol from set [b|k|m], dictionary size will be calculated as DictionarySize = 2^Size bytes. For decompressing 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 doesn't provide good compression ratio, but they often works pretty fast in combination with fast mode (a=0). Memory requirements depend from 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: Operation system also needs some amount of physical memory for system's purposes. So keep at least 32MB of physical memory unused.

fb={N}

Sets number of fast bytes for LZMA. It can be in range from 5 to 273. Default value is 32 for normal mode and 64 for maximum and ultra modes. Usually 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 big number gives a little bit better compression ratio and slower compression process. For example, mf=HC4 and mc=10000 can provide almost same compression ratio as mf=BT4.

lc={N}

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

PPMd

PPMd is a PPM-based algorithm. This algorithm is mostly based on Dmitry Shkarin's PPMdH sources. PPMd provides very good compression ratio for plain text files. There is no difference between compressing speed and decompressing speed. Memory requirements for compressing and decompressing 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 size of used memory for PPMd. You must specify size in bytes, kilobytes, or megabytes. The maximum value is 2GB = 2^31 bytes. Default value is 24 (16MB). If you do not specify any symbol from set [b|k|m], memory size will be calculated as (2^Size) bytes. PPMd uses the same amount of memory for compressing and decompressing.

o={Size}

Sets model order for PPMd. Size must be in range [2,32]. Default value is 6.

BCJ2

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

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

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. Compressing 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),