Amiga Old File System: Difference between revisions

Revision as of 08:13, 8 July 2005

Revision as of 14:28, 15 October 2005

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== History ==

Originally known as Amiga File System, the filesystem itself was very similar to that of [[Xerox]] Alto Filesystem. Development was from 1982 to 1985 as the filesystem of [[TripOS]]. It received the nickname of "Old" when [[Amiga Fast File System|Fast File System]] was released with [[Amiga OS]] 1.3.

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== Characteristics ==

Amiga uses [[MFM]] encoding/decoding by default when handling [[floppy disk]]s. There are 80 cylinders on an Amiga floppy disk. Each cylinder has 2 MFM tracks, 1 on each side of the disk. Double density (DD) disks have 11 sectors per MFM track, High density (HD) disks have 22 sectors.

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The exact calculation for where it is stored is as follows:

<math>numCyls = highCyl - lowCyl + 1 </math>

<math>highKey = numCyls * numSurfaces * numBlocksPerTrack - 1 </math>

<math>rootKey = INT (numReserved + highKey) / 2 </math>

The Rootblock contains information about the disk: its name, its formatting date, etc. It also contains information on accessing the files/directories/links located at the uppermost (root) directory.

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There was a bug in the old AmigaDOS versions when applying the Hash function to international characters (ASCII codes > 128). Consequently, FFS was then created with the 'international mode' (INTL). Filename characters can be lowercase and uppercase, but are not case sensitive.

Files are comprised of a file header block, which contains information about the file (size, last access time, data block pointers, ETC), and the data blocks, which contain the actual data. The file header block contains up to BSIZE/4-56 data block pointers (which amounts to 72 bytes with the usual 512 byte blocks). If a file is larger than that, file extension blocks will be allocated to hold the data block pointers. File extension blocks are organised in a linked list, which starts in the File header block ('extension' field).

== See also ==

*[[Amiga Fast File System]]

*[[Professional File System]]

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== External links ==

*[http://lclevy.club.fr/adflib/index.html The ADFlib Page] and precisely [http://lclevy.club.fr/adflib/adf_info.html ADF File specs]

*[ftp://it.aminet.net/pub/aminet/disk/misc/ADFlib.lha The ADF specs] in [[LHA (file format)|LHA]] format, from [[Aminet]]