


ARCFS(5)                  FILE FORMATS                   ARCFS(5)



NAME
     ArcFS - Archive file format for the RISC OS ArcFS filesystem

CONVENTIONS
     Strings are given in ASCII with  C-style  escapes.  No  ter-
     minating   is present if not explicitly included.

     Words are 32 bit little-endian numbers.

     Half words are 16 bit little-endian numbers.

     This document describes format version 0, for ArcFS  minimum
     versions  0.40  and  1.00, and version 0a, for ArcFS minimum
     versions 0.58 and 2.17.


FORMAT
     The file consists of a file header, a  sequence  of  archive
     headers, then a sequence of compressed files.


FILE HEADER
     File string signature
     The string "Archive" followed by a zero byte.

     Header length
     Length of header info in bytes, one word, multiple of 36.

     Data offset
     Offset, in bytes, into archive at  which  data  starts,  one
     word.

     Read-only version
     Minimum read-only version required, multiplied by  100,  one
     word.

     Read-write version
     Minimum read--write version required, multiplied by 100, one
     word.

     Reserved
     Reserved for future use, 68 bytes.


ARCHIVE HEADER
     The last header starts at 60+length of headers and  ends  at
     96+length  of  headers. The format of each header is as fol-
     lows.

     Info byte
     Object information byte, show compression method used:
          0x00 end of directory marker



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ARCFS(5)                  FILE FORMATS                   ARCFS(5)



          0x01 object has been deleted
          0x82 stored
          0x83 packed
          0x88 crunched
          0xFF compressed

     File name
     File name, 11 bytes.

     Full length
     Original file length, or 0xFFFFFFFF for  a  directory),  one
     word.

     Load address
     Load address of the file, or 0xFFFFFFdd  for  a  directory),
     one word.

     Exec address
     Exec address of the file, or 0xdddddddd  for  a  directory),
     one word.

     File load and execution address may contain a  filetype  and
     datestamp as normal.

     Directories can be date-stamped, the number of  centiseconds
     since  the  1st  January 1900 when the directory was created
     are given by &dddddddddd contained in the  directory's  load
     and execution addresses as shown above.

     Archives converted from spark(5) format using  ArcConv  will
     have  the  same full length, compressed length, load address
     and execute address as they had in the Spark archive.

     Attributes
     Attributes of the file, one word.  Contains  the  number  of
     bits  compression  for  crunch and compress format files and
     the least significant bytes contains the  standard  RISC  OS
     information on file access.

     Compressed length
     Length of compressed data, or 0xFFFFFFFF  for  a  directory,
     one word.

     Information word
     The top bit (definitively) indicates whether the object is a
     file or a directory, 0 for a file, 1 for a directory.

     In the case of a file, the least significant  31  bits  show
     the offset from the start of data at which the file data can
     be found.

     In the case of a directory, the least  significant  31  bits



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ARCFS(5)                  FILE FORMATS                   ARCFS(5)



     show  the offset from the start of headers (96) at which the
     next object in this directory can be  found,  the  following
     object being the first in the sub-directory.


FORMAT VERSION 0a
     This archive format is backwards  compatible  with  versions
     0.40  and  1.00,  the  only difference being that there is a
     block of catalogue  information  immediately  prior  to  the
     start of each file's data as described below.

     Note that this information is there to aid the  recovery  of
     most  files  in  the  event of archive corruption and is not
     used by ArcFS.

     Note, also that Compact and Autocompact in release  versions
     1.09,  2.02 and 2.11 will compact out the catalogue informa-
     tion blocks, so try to avoid writing to  new  archives  with
     old versions of ArcFS.

     Marker
     A marker to indicate the start of a file, the string "FileData", not terminated.

     Info byte
     One byte, as above.

     Leaf name
     The file name, 11 bytes.

     Full length
     One word, as above.

     Load address
     One word, as above.

     Exec address
     One word, as above.

     Attributes
     One word, as above.


SEE ALSO
     spark(5), nspark(1)











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