ARC file header structure
Byte number Value(s) Meaning
--------------------------------------------------------------
0 $1A Header Flag
1 0-9 Compression method
2-14 --- Filename.
15-18 --- Compressed file size.
19-20 bits Date format
15-9 Year
8-5 Month
4-0 Day
21-22 bits Time format
15-11 Hours (military)
10-5 Minutes
4-0 Seconds
23-24 --- CRC-16
25-28 --- Original file size
Compression method
------------------
1 unpacked (obsolete)
2 unpacked
3 packed
4 squeezed (after packing)
5 crunched (obsolete)
6 crunched (after packing) (obsolete)
7 crunched (after packing, using faster hash algorithm)
8 crunched (after packing, using dynamic LZW variations)
9 Squashed c/o Phil Katz (no packing) (var. on crunching)
NOTE: LZW is Lempel-Ziv-Welch compression algorithm
LZH
---
LZH file header structure
Byte number Value(s) Meaning
--------------------------------------------------------------
0 --- Header size
1 --- Cksum of remaining bytes
2-6 --- Method
7-10 --- Compressed size
11-14 --- Uncompressed size
15-16 --- Time format
17-18 --- Date format
19-20 --- File attribute
21-22 --- Filename/path length
23-XX --- Filename/path
XX+1-XX+2 --- CRC-16
Compression method
------------------
-lh0- No compression used
-lh1- LZW, 4K buffer, Huffman for upper 6 bits of pos
-lz4- LZW, Arithmetic Encoding
-lz5- LZW, Arithmetic Encoding
ZIP
---
ZIP file header structures
Local File Header
-----------------
Byte number Value(s) Meaning
--------------------------------------------------------------
0-3 $04034B50 Local File Header Signature
4-5 --- Version needed to extract
6-7 --- General purpose bit flag
8-9 0-6 Compression method
10-11 --- Time
12-13 --- Date
14-17 --- CRC-32
18-21 --- Compressed size
22-25 --- Uncompressed size
26-27 --- Filename length
28-29 --- Extra field length
30-XX --- path/filename
XX+1-YY --- extra field
Central Directory Structure
---------------------------
Byte number Value(s) Meaning
--------------------------------------------------------------
0-3 $02014B50 Central file header signature
4 --- Version made by
5 --- Host operating system
6 --- Version needed to extract
7 --- O/S of version needed for extraction
8-9 --- General purpose bit flag
10-11 0-6 Compression method
12-13 --- Time
14-15 --- Date
16-19 --- CRC-32
20-23 --- Compressed size
24-27 --- Uncompressed size
28-29 --- Filename length
30-31 --- Extra field length
32-33 --- File comment length
34-35 --- Disk number start
36-37 bit Internal file attributes
0 if = 1, file is apparently an ASCII
or text file
0 if = 0, file apparently contains
binary data
1-7 unused in version 1.0.
38-41 --- External file attributes, host
system dependent
42-45 --- Relative offset of local header
from the start of the first disk
on which this file appears
46-XX --- Filename or path - should not
contain a drive or device letter,
or a leading slash. All slashes
should be forward slashes '/'
XX+1-YY --- extra field
YY+1-ZZ --- file comment
End of Central Directory Structure
----------------------------------
Byte number Value(s) Meaning
--------------------------------------------------------------
0-3 $06064B50 End of central dir signature
4-5 --- Number of this disk
6-7 --- Number of disk with start central dir
8-9 --- Total number of entries in central dir
on this disk
10-11 --- total number entries in central dir
12-15 --- Size of the central directory
16-19 --- Offset of start of central directory
with respect to the starting disk
number
20-21 --- zipfile comment length
22-XX --- zipfile comment
ZIP Values
----------
Host O/S
Value Description Value Description
----- -------------------------- ----- ------------------------
0 MS-DOS and OS/2 (FAT) 5 Atari ST
1 Amiga 6 OS/2 1.2 extended file sys
2 VMS 7 Macintosh
3 *nix 8 thru
4 VM/CMS 255 unused
General Purpose Bit Flag
Bit Description
--------- -----------------------------------------
0 If set, file is encrypted
1 If file Imploded and this bit is set, 8K
sliding dictionary was used. If clear, 4K
sliding dictionary was used.
2 If file Imploded and this bit is set, 3
Shannon-Fano trees were used. If clear, 2
Shannon-Fano trees were used.
3-4 unused
5-7 used internally by ZIP
Note: Bits 1 and 2 are undefined if the compression method is
other than type 6 (Imploding).
Compression Method
Name Method Description
----------- ------ --------------------------------------------
Stored 0 No compression
Shrunk 1 LZW, 8K buffer, 9-13 bits with partial clearing
Reduced-1 2 Probalistic compression, lower 7 bits
Reduced-2 3 Probalistic compression, lower 6 bits
Reduced-3 4 Probalistic compression, lower 5 bits
Reduced-4 5 Probalistic compression, lower 4 bits
Imploded 6 2/3 Shanno-Fano trees, 4K/8K sliding dictionary
ZOO
---
ZOO file header sturtures
Master Header
-------------
Byte number Value(s) Meaning
--------------------------------------------------------------
0-19 --- Archive header text
20-23 $A7DCFDC4 File signature
24-27 --- pointer to 1st header
28-31 --- pointer to 1st header - 1
32 --- version making archive
33 --- minimum version needed to extract
File Header
-----------
Byte number Value(s) Meaning
--------------------------------------------------------------
0-3 $A7DCFDC4 signature
4 --- type of directory entry
5 0-1 Compression method
6-9 --- position of next dir entry
10-13 --- position of header
14-15 --- Date
16-17 --- Time
18-19 --- CRC-16
20-23 --- Uncompressed size
24-27 --- Compressed size
28 --- version that made this file
29 --- minimum version needed to extract
30 0-1 1 if file deleted from archive
31-34 --- pointer to comment, 0 if none
35-36 --- length of comment
37-XX --- path/filename
Compression Method
NAME DESCRIPTION
----------- --------------------------------------------
Stored No compression used
Crunched Packing, LZW, 4K buffer, var len (9-13 bits)