AmigaDOS: История и особенности операционной системы AmigaOS

Disk operating system of the AmigaOS

AmigaDOS is the disk operating system of the AmigaOS, which includes file systems, file and directory manipulation, the command line interface, and file redirection. In AmigaOS 1. x, AmigaDOS is based on a TRIPOS port by MetaComCo, written in BCPL. BCPL does not use native pointers, so the more advanced functionality of the operating system was difficult to use and error prone. The third party AmigaDOS Resource Project (ARP, formerly the AmigaDOS Replacement Project), a project begun by Amiga developer Charlie Heath, replaced many of the BCPL utilities with smaller, more sophisticated equivalents written in C and assembler, and provided a wrapper library, arp. library. This eliminated the interfacing problems in applications by automatically performing conversions from native pointers (such as those used by C or assembler) to BCPL equivalents and vice versa for all AmigaDOS functions. From AmigaOS 2. x onwards, AmigaDOS was rewritten in C, retaining 1. x compatibility where possible. Starting with AmigaOS 4, AmigaDOS abandoned its legacy with BCPL. Starting from AmigaOS 4.1, AmigaDOS has been extended with 64 bit file access support.

The Amiga console is a standard Amiga virtual device, normally assigned to CON: and driven by console. handler. It was developed from a primitive interface in AmigaOS 1.1, and became stable with versions 1.2 and 1.3, when it started to be known as AmigaShell and its original handler was replaced by newconsole. handler (NEWCON:). The console has various features that were considered up to date when it was created in 1985, like command template help, redirection to null ("NIL:"), and ANSI color terminal. The new console handler – which was implemented in release 1.2 – allows many more features, such as command history, pipelines, and automatic creation of files when output is redirected. When TCP/IP stacks like AmiTCP were released in the early 1990s, the console could also receive redirection from Internet enabled Amiga device handlers (e. g., TCP:, ). Unlike other systems originally launched in the mid 1980s, AmigaDOS does not implement a proprietary character set; the developers chose to use the ANSI–ISO standard ISO 8859 1 (Latin 1), which includes the ASCII character set. As in Unix systems, the Amiga console accepts only linefeed ("LF") as an end of line ("EOL") character. The Amiga console has support for accented characters as well as for characters created by combinations of 'dead keys' on the keyboard.

A user can terminate a program by invoking the key combination or Pressing or any printing character on the keyboard suspends the console output. Output may be resumed by pressing the key (to delete all of the input) or by pressing (which will cause the input to be processed as a command as soon as the current command stops running).

AmigaDOS is in general case insensitive. Indicating a device as "Dh0:", "DH0:" or "dh0:" always refers to the same partition; however, for file and directory names, this is filesystem dependent, and some filesystems allow case sensitivity as a flag upon formatting. An example of such a file system is Smart File System. This is very convenient when dealing with software ported over from the mostly case sensitive Un*x world, but causes much confusion for native Amiga applications, which assume case insensitivity. Advanced users will hence typically only use the case sensitivity flag for file systems used for software originating from Un*x. Re casing of file, directory and volume names is allowed using ordinary methods; the commands "rename foo Foo" and "relabel Bar: bAr:" are valid and do exactly what is expected, in contrast to for example on Linux, where "mv foo Foo" results in the error message "mv: `foo' and `Foo' are the same file" on case insensitive filesystems like VFAT.

Partitions and physical drives are typically referred to as DF0: (floppy drive 0), DH0: (hard drive 0), etc. However, unlike many operating systems, outside of built in physical hardware devices like DF0: or HD0:, the names of the single disks, volumes and partitions are totally arbitrary: for example a hard disk partition could be named Work or System, or anything else at the time of its creation. Volume names can be used in place of the corresponding device names, so a disk partition on device DH0: called Workbench could be accessed either with the name DH0: or Workbench:. Users must indicate to the system that "Workbench" is the volume "Workbench:" by always typing the colon ":" when they are entering information in a requester form or into AmigaShell. If an accessed volume name cannot be found, the operating system will prompt the user to insert the disk with the given volume name, or allow the user to cancel the operation. In addition, logical device names can be set with the "assign" command to any directory or device; programs often assigned a virtual volume name to their installation directory (for instance, a fictional word processor called Writer might assign Writer: to DH0:Productivity/Writer). This allows for easy relocation of installed programs. The default name SYS: is used to refer to the volume that the system was booted from. Various other default names are provided to refer to important system locations. e. g. S: for startup scripts, C: for AmigaDOS commands, FONTS: for installed fonts, etc. Assignment of volume labels can also be set on multiple directories, which will be treated as a union of their contents. For example, FONTS: might be assigned to SYS:Fonts, then extended to include, for example, Work:UserFonts using the add option of the AmigaDos assign command. The system would then permit use of fonts installed in either directory. Listing FONTS: would show the files from both locations.

The physical device shares the same floppy drive mechanics with , which is the CrossDOS virtual device capable of reading PC formatted floppy disks. When any PC formatted floppy disk is inserted into the floppy drive, then the floppy Amiga icon will change to indicate that the disk is unknown to the normal Amiga device, and it will show four question marks as the standard "unknown" volume name, while the icon will appear revealing the name of the PC formatted disk. Any disk change with Amiga formatted disks will invert this behaviour.

AmigaDOS supports various filesystems and variants. The first filesystem was simply called Amiga FileSystem, and was suitable mainly for floppy disks, because it did not support automatic booting from hard disks (on floppy, booting was done using code from the bootblock). It was soon replaced by FastFileSystem (FFS), and hence the original filesystem was known by the name of "Old" FileSystem (OFS). FFS was more efficient on space and quite measurably faster than OFS, hence the name. With AmigaOS 2. x, FFS became an official part of the OS and was soon expanded to recognise cached partitions, international partitions allowing accented characters in file and partition names, and finally (with MorphOS and AmigaOS 4) long filenames, up to 108 characters (from 31). Both AmigaOS 4. x and MorphOS featured a new version of FFS called FastFileSystem 2. FFS2 incorporated all of the features of the original FFS including, as its author put it, "some minor changes". In order to preserve backwards compatibility, there were no major structural changes. (However, FF2 on AmigaOS 4.1 differs in that it can expand its features and capabilities with the aid of plug ins). As with FFS2, the AmigaOS 4 and MorphOS version of Smart FileSystem is a fork of original SFS and are not 100% compatible with it. Other filesystems like FAT12, FAT16, FAT32 from Windows or ext2 from Linux are available through easily installable (drag and drop) system libraries or third party modules such as FAT95 (features read/write support), which can be found on the Aminet software repository. MorphOS 2 has built in support for FAT filesystems. AmigaOS 4.1 adopted a new filesystem called JXFS capable to support partitions over a terabyte of size. Alternate filesystems from third party manufacturers include Professional FileSystem, which is a filesystem with an easy structure, based on metadata, allowing high internal coherence, capable of defragmenting itself on the fly, and does not require to be unmounted before being mounted again; and Smart FileSystem which is a journaling filesystem which performs journaled activities during system inactivities, and has been chosen by MorphOS as its standard filesystem.

With the July 2007 Update of AmigaOS 4.0 in 2007, the first two plug ins for FFS2 were released:
fs plugin cache: increases performance of FFS2 by introducing a new method of data buffering. fs plugin encrypt: data encryption plug in for partitions using the Blowfish algorithm.

AmigaDOS has only a single mandated filename extension: ". info", which must be appended to the filename of each icon. If a file called myprog exists, then its icon file must be called myprog. info. In addition to image data, the icon file also records program metadata such as options and keywords, its own position on the desktop (AmigaOS can "snapshot" icons in places defined by the user), and other information about the file. Directory window size and position information is stored in the ". info" file associated with the directory, and disk icon information is stored in "Disk. info" in the root of the volume. With the exception of icons, the Amiga system does not identify file types using extensions, but instead will examine either the icon associated with a file or the binary header of the file itself to determine the file type.