Amiga Old File System: Difference between revisions

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{{Short description|File system for AmigaOS}}

{{one source|date=October 2015}}

On the [[Amiga]], the '''Old File System''', sometimes also called ''Amiga File System'', was the filesystem for [[Amiga OSAmigaOS]] before the [[Amiga Fast File System]]. Even though it used 512-byte blocks, it reserved the first small portion of each [[Block (data storage)|block]] for [[Metadata (computing)|metadata]], leaving an actual data block capacity of 488 bytes per block. It wasn't very suitable for anything except [[floppy disk]]s, and it was soon replaced.

== History ==

OriginallyCommonly known as just the ''Amiga File System'', theit filesystemoriginally itselfcame wasfrom verythe similar to thatfilesystem of [[XeroxTRIPOS]], Altowhich Filesystem.formed Developmentthe wasbasis fromof 1982the tofirst 1985 as the filesystemversions of [[TripOSAmigaDOS]]. It received the nickname of "Old" or "Original" File System when [[Amiga Fast File System|Fast File System]] was released with [[Amiga OS]]AmigaOS 1.3.

OFS is very good for repairing the filesystem in the event of a problem, although the so-called DiskDoctor provided by Commodore quickly earned the name DiskDestroyer, because it could not repair No-DOS type autostart disks provided by third-party software manufacturers as bootable disks for games. The idea to create non-standard autobootable disks was born in a primitive attempt to prevent copy of such disks and to avoid the loading and launch of Amiga DOS, in order to directly access the Amiga graphic, audio and memory chipsets. DiskDoctor in fact changed autostart disks bootblocks into standard AmigaDOS-based ones, renaming a disk with "Lazarus" namedisk, and made the autostart disk unusable.<ref>[http://www.amiga.org/forums/showthread.php?t=72730 Why was "Disk doctor" so spectacularly bad at its job?]</ref>

Metacomco, BSTRINGS, BPOINTERS, and family contained in the Amiga FS entered the scene{{Clarify|date=August 2011}} when it was decided that the originally planned OS would take too long to be developed in time for the launch of Amiga. Consequently, Metacomco grafted onto the filesystem a lot of things{{Specify|date=August 2011}} that the old Amiga Inc. has changed.

== Characteristics of AmigaDOS Floppy Disks ==

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==Characteristics of Files under AmigaDOS==

Prior to AmigaOS 3.5, AmigaDOS file handles maintained a 32 -bit wide offset parameter (unsigned), telling where to start the next read or write operation. The biggest size for any single Amiga file under these operating systems therefore comes to 2³² = 4 [[gibibyte|GiB]]. After Amiga OS 3.5, file handles may reference 2⁶⁴ = 16 [[exbibyte|EiB]] files. However, OFS-formatted disks continue to retain the 32-bit limitations, for that is an intrinsic limitation of the format as recorded on the media.

An OFS datablock stores block size BSIZE-24 bytes (i.e. normally 488 bytes at most frequently used BSIZE of 512 bytes).

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== External links ==

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

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{{AmigaOS}}