Archive files are files that contain the content of other files. They are a useful method of holding, moving and copying multiple files without having to deal with each and every individual file itself. They usually also contain metadata relating to those files, so being a useful method of being able to transport that metadata when the storage medium itself cannot hold it.
Archive file formats
Archive files typically used with Acorn systems are GetBack, Black, CJR and ZIP files.
Written by Acorn as a tool to back up file server contents, implemented with an archiver called Archive and a dearchiver called GetBack.
The format of an Acorn GetBack archive is as follows Repeated for each file: n bytes : filename, <cr> 1 byte : filetype - 1=file, 2=directory 1 byte : disk number - starts at 1 4 bytes : load address 4 bytes : exec address 4 bytes : length - should be ignored if filetype=2 1 byte : access byte 2 bytes : modification date in NetFS format 2 bytes : modification time hh, mm (no seconds) length x bytes of file data Stored filenames are the full path of the entry, often with an absolute directory reference, eg "$.CAVE", "$.CAVE.!BOOT". If the stored filename starts with '.', the initial '.' is skipped. Entries can be in any order, but will tend to be in the order that they were encounted when adding them to the archive.
Originally designed by Andrew Black in 1991, implemented with an archiver/dearchive program called Archive.
The format of a Black archive is as follows A version 2 Black archive starts with a 'dummy' header to prevent earlier versions from extracting incorrectly: Read using INPUT# 0000 "" - ie, null string, ie 00, 00 0002 ( filelength-17 ) OR &FF000000 0007 dummy load% - set to zero 000C dummy exec% - set to zero 0011 rest of file starts here Repeated for each file: Read using INPUT#: name$ Filename len% length load% load address exec% execute address Version 2 archives then have: attr% file attributes Read using BGET: The bytes of the file Archive version before 2.10 will read a version 2 archive file as a single entry with the flag set to 'ignore this data'. Archive version 2.10 onwards can read version 1 archive files and version 2 archive files.
Originally written by Chris Richardson at 8BS. It has a fixed-sized header containing a list of up to 51 files, so
The format of a CJR archive is as follows Read using INPUT#: 0000 ptr%(0) \ 0005 ptr%(1) \ 000A ptr%(2) } Pointers to entries : / 00FA ptr%(50)/ 00FF Each entry: Read using INPUT#: name$ filename load% load address exec% execution address len% file length attr% file attributes Read using BGET: The bytes of the file If a pointer is zero, it doesn't point to anything. Usually, the files run straight after each other. Current versions of Archive cannot cope with null pointers in the middle of the pointer list. With Black and CJR archives the bottom three bytes of len% is the actual data length occupied within the archive, even if this data expands to form a larger file. The top byte of len% is a flag. Current meanings are as follows: &00 File <>&00 Not a file &FF Ignore this data
Disk images are sometimes used as archive files, particularly images of a single DFS filesystem.