The ARC files are archive files created by the SEA ARC program. The compression has been superceded by more recent compression programs. Similar archives can be created by the PAK and PkPAK programs. There have been many variations and enhancements to the ARC format though not as many as to the TIFF format. You may have to use some (paranoid) checks to ensure that you actually are processing an ARC file, since other archivers also adopted the idea of putting a 01Ah byte at offset 0, namely the Hyper archiver. To check if you have a Hyper-archive, check the next two bytes for "HP" or "ST" (or look below for "HYP"). Also the ZOO archiver also does put a 01Ah at the start of the file, see the ZOO entry below. OFFSET Count TYPE Description 0000h 1 byte ID=1Ah 0001h 1 byte Compression method (see table 0001) 0002h 12 char File name 000Fh 1 dword Compressed file size 0013h 1 dword File date in MS-DOS format (see table 0009) 0017h 1 word 16-bit CRC 0019h 1 dword Original file size ="SIZ" (Table 0001) ARC compression types 0 - End of archive marker 1 - unpacked (obsolete) - ARC 1.0 ? 2 - unpacked - ARC 3.1 3 - packed (RLE encoding) 4 - squeezed (after packing) 5 - crunched (obsolete) - ARC 4.0 6 - crunched (after packing) (obsolete) - ARC 4.1 7 - crunched (after packing, using faster hash algorithm) - ARC 4.6 8 - crunched (after packing, using dynamic LZW variations) - ARC 5.0 9 - Squashed c/o Phil Katz (no packing) (var. on crunching) 10 - crushed (PAK only) 11 - distilled (PAK only) 12-19 - to 19 unknown (ARC 6.0 or later) - ARC 7.0 (?) 20-29 - ?informational items? - ARC 6.0 30-39 - ?control items? - ARC 6.0 40+ - reserved According to SEA's technical memo, the information and control items were added to ARC 6.0. Information items use the same headers as archived files, although the original file size (and name?) can be ignored. OFFSET Count TYPE Description 0000h 2 byte Length of header (includes "length" and "type"?) 0002h 1 byte (sub)type 0003h ? byte data Informational item types as used by ARC 6.0 : Block type Subtype Description 20 archive info 0 archive description (ASCIIZ) 1 name of creator program (ASCIIZ) 2 name of modifier program (ASCIIZ) 21 file info 0 file description (ASCIIZ) 1 long name (if not MS-DOS "8.3" filename) 2 extended date-time info (reserved) 3 icon (reserved) 4 file attributes (ASCIIZ) Attributes use an uppercase letter to signify the following: R read access W write access H hidden file S system file N network shareable 22 operating system info (reserved) (Table 0009) Format of the MS-DOS time stamp (32-bit) The MS-DOS time stamp is limited to an even count of seconds, since the count for seconds is only 5 bits wide. 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 |<---- year-1980 --->|<- month ->|<--- day ---->| 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 |<--- hour --->|<---- minute --->|<- second/2 ->| EXTENSION:ARC,PAK OCCURENCES:PC PROGRAMS:SEA ARC,PAK,PkPAK SEE ALSO: HYP,ZOO VALIDATION:FileSize="SIZ"
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