AmigaOS
AmigaOS is the default native
operating system of the
Amiga personal computer. On top of a basic
kernel called
Exec, it includes an abstraction of the Amiga's unique hardware, a disk operating system called
AmigaDOS, a windowing system called
Intuition and a graphical user interface called
Workbench.
AmigaOS can be divided into two parts: the
Kickstart (
ROM) and
Workbench disks. It used to be the case that versions of Kickstart and Workbench were released together, for use with each other. From Workbench 3.5 onwards, the first release after
Commodore International stopped development, AmigaOS has become software-only, standardising on Kickstart version 3.1 in ROM.
Kickstart
 |
The image shown by Amiga OS 1.x on start-up, asking the user to insert the kickstart disk. |
Kickstart is the name given to the
bootstrap ROM. On the first
Amiga model, the
A1000, this was loaded from disk, although eventually the Kickstart was embedded in a ROM chip inside the computer. The Amiga 1000 could be modified to take these chips, and subsequent Amiga models all used ROM chips.
Kickstart contained the code needed to boot the standard Amiga hardware and any
Autoconfig expansion hardware. The Kickstart also contained many stock parts of the Amiga's operating system, such as
Exec,
Intuition and the core of
AmigaDOS. This meant that a powered-on Amiga already had a lot of the essential parts of the operating system available. Later versions of the Kickstart contained drivers for
IDE and
SCSI controllers,
PCMCIA ports and various other hardware that came built into Amigas. It can be compared to the
BIOS in
IBM PCs, however it has far more functionality available at boot time - the full windowing environment, for example.
With third party
software, it is possible to have a different Kickstart loaded in RAM and to use it instead of the ROM one - for example Kickstart 1.3 may be loaded in order to run old games incompatible with Kickstart 2.0 and higher. These programs are called
softkickers. There are also hardware
Kickstart switchers which allow you to have more than one set of Kickstart chips inside the computer, which are selectable either by a switch or a keyboard shortcut when you first turn the machine on.
Workbench
Workbench is the name given to both the core operating system software that is not stored in the Kickstart ROM (the "Workbench disk"), and also the native graphical
shell for the
Amiga computer. The Workbench environment does not have to be loaded for software to run. In fact, to take over the Amiga hardware and keep all memory and resources to themselves, many games boot directly from Kickstart (using a custom
bootblock on the
floppy disk).
As the name suggests, the
metaphor of a
workbench is used, rather than a desktop; directories are depicted as
drawers, executable files are
tools, data files are
projects and GUI widgets are
gadgets. In many other aspects the interface resembles
Mac OS, with the main desktop showing icons of inserted disks, and a single menu bar at the top of every screen. Unlike the Macintosh, the standard Amiga mouse has two buttons – the right mouse button operates the pull-down menus, with a Macintosh-style "release to select" mechanism.
A unique feature of Workbench is
multiple screens. These are conceptually similar to
X Window System virtual desktops or workspaces, but are generated dynamically by application programs as necessary. Each screen can have a different resolution and colour depth. A gadget in the top-right corner of the screen allows screens to be cycled - as the OS stores all screens in memory simultaneously, redrawing is instantaneous. Screens can also be dragged up and down by their title bars, on older Amigas this functionality was provided by the custom chipsets specially designed for the platform, since AmigaOS4 a new technique is adopted and the screens are draggable in any direction. Drag and drop between different screens is possible too.
Underlying the Workbench is the
Intuition windowing system. This controls and draws screens, windows, gadgets and handles input from the keyboard and mouse, passing messages to programs.
Workbench 2.0 user interface improvements
Until Workbench 2.0, there was no unified
look and feel design standards - application developers had to write their own widgets (both buttons and menus), with Intuition providing minimal support. With Workbench 2.0 came
gadtools.library, which provided standard widget sets, and the
Amiga User Interface Style Guide, which explained how applications should be laid out for consistency.
Workbench 2.0 also added support for
public screens. Instead of the Workbench screen being the only shareable screen, applications could create their own named screens to share with other applications.
Workbench 2.0 introduced
AmigaGuide, a simple text-only
hypertext markup scheme and browser, of providing online help inside applications. It also introduced
Installer, a standard software installation program, driven by a
LISP-like scripting language.
Finally, Workbench 2.0 rectified the problem of developers
hooking directly into the input-events stream to capture keyboard and mouse movements, often locking up the whole system. Workbench 2.0 provided
Commodities, a standard interface for modifying or scanning input events. This included a standard method for specifying global "hotkey" key-sequences, and a
Commodities Exchange registry for the user to see what commodities were running.
Workbench icons
The
icons that Workbench uses to represent the files in a volume or a drawer are stored in special
.info files, with the name of the
.info file matching the name of the file it represents. For example, the icon for
NotePad, a
text editor, is found in the file
NotePad.info.
The
.info file includes the graphical representation of the icon and its position in the volume or drawer window. The icon also specifies the type of the file, as used by Workbench. Workbench recognises five different file types:
* Tool: An executable program.
* Project: A data file of an executable program. The program which created the file is named in the icon file, double-clicking on the icon loads the program that created it.
* Drawer: A directory containing files, and other drawers.
* Volume: A physical disk or a
RAM disk.
* Garbage: The Trashcan - a deleted file backup, which works in a similar way to the '
Recycle bin' in
Microsoft Windows.
Tool files can include "tool types" in the
.info file. These are used as configuration options for the program. Each tool type is a single line of text, which can optionally include parameters, written after an
= sign. Tool types can be commented out by writing them in
parentheses. For example, the tooltype "
CX_POPKEY=ctrl alt f1" says that the application (a
Commodity) will pop up the user interface in response to the key sequence Ctrl-Alt-F1.
The colours used in the icon are normally only stored as indices to the Amiga Workbench screen's current palette. Because of this, the icons' colour scheme is inherently tied to the chosen hues in the screen's palette, and choosing non-standard colours can give the icons an ugly appearance. This problem was party solved by a third-party system called
NewIcons, which adds additional features to the standard
.info files. Unlike normal Workbench icons, NewIcons include actual
RGB colour information, and the system tries its best to match the icons' colour hues to those in the screen palette.
Since AmigaOS 3.5, Workbench supports icons with up to 256 colors, still based on the screen palette. This release of AmigaOS features the
Glowicons icon set by
Matt Chaput. With AmigaOS 4.0, a screen palette independent system is used. The 4.0 icons, designed by
Martin Merz, can use a palette of 256 colors each.
AmigaDOS
AmigaDOS provides the
disk operating system portion of the AmigaOS. This includes
file systems, file and directory manipulation, the
command line interface, file redirection and so on.
In AmigaOS 1.x, the AmigaDOS portion was based on a
TRIPOS port by
MetaComCo, written in
BCPL. The more advanced functionality was only available to programs written in BCPL,
C programmers were left in the cold. The third-party
AmigaDOS Resource Project (arp.library) [
1] provided the advanced functionality to C programmers. ARP also provided one of the first standardised
file requesters for the Amiga.
From AmigaOS 2.x onwards, AmigaDOS was rewritten in
C, retaining 1.x compatibility where possible.
Graphics
Up to version 3, AmigaOS only supported the
native Amiga graphics chipset, via
graphics.library. This led developers to avoid OS functionality for drawing, and go straight for the underlying hardware. Third-party graphics cards were only supported via unofficial solutions. The ideal situation, where the AmigaOS could directly support any graphics system, was termed
retargetable graphics (RTG) [
2]. Release 3.1 included some support for third party graphics cards, such as the Picasso. With AmigaOS 3.5, some RTG systems were bundled with the OS, allowing the use of common hardware cards other than the native Amiga chipsets. The main RTG systems are
CyberGraphX,
Picasso 96 and
EGS.
The Amiga did not have any official
3D graphics capability, so it had no standard 3D graphics interface. Graphics card manufacturers provided their own standards, which include
MiniGL,
Warp3D, Storm
Mesa (
agl.library) and
CyberGL.
VideoScape 3D was one of the earliest 3D rendering & animation systems, as well as
TrueSpace 3D.
Likewise, while the Amiga is well known for its ability to easily
genlock with video, it had no built in
video capture interface. Third party interfaces included
Digiview,
VHI (Video Hardware Interface) by IOSPIRIT GmbH,
tv.library by Elbox Computer and
tvcard.library by Guido Mersmann.
Audio
Up to version 3.1, AmigaOS only supported the original Amiga chipset's sound capabilities, via
audio.device. Support for third-party audio cards was vendor-dependent, until the creation and adoption of
AHI [
3] as a de facto standard. AmigaOS itself did not support
MIDI, but David Joiner's
camd.library provided a specific MIDI support library.
Speech synthesis
The original Amiga was launched with
speech synthesis software, developed by Softvoice, Inc. [
4] This could be broken into three main components:
narrator.device, which could play and modulate all
phonemes used in
American English,
translator.library, which could translate english text to American English phonemes, and the
SPEAK: handler, which command-line users could redirect output to, to have it spoken.
In the original 1.x releases, a
Say program demo included with
AmigaBASIC programming examples. For 2.0,
Say became a standard utility program which did not need AmigaBASIC.
The speech synthesiser was occasionally used in third-party programs, often educational software. The word processor Prowrite could read out documents using the synthesiser.
Despite the limitation on the
narrator.device's phonemes, Francesco Devitt wrote a new version of
translator.library which could translate any language to phonemes, given it had a set of rules for that language, and thus provided multilingual speech synthesis. [
5]
ARexx
Main article: ARexx
The Amiga OS had support for the
Rexx language. It was called ARexx (short for "Amiga Rexx") and was a script language which allowed for full OS scripting, similar to
Bash on Linux, intra-application scripting, similar to VBA in Microsoft Office, as well as inter-program communication. Having a single scripting language for any application on the operating system was beneficial to users, instead of having to learn a new language for each application.
Programs could listen on an "ARexx port" for string messages. These messages could then be interpreted by the program in a similar fashion to a user pushing buttons. For example, an ARexx script when run in an e-mail program, could save the currently displayed email and invoke an external program which could extract and process information and then invoke a viewer program. This allowed applications to control other applications, send data back and forth directly with memory handles, instead of saving files to disk then reloading.
RAM Disk
The Amiga OS has a dynamically sized RAM disk, which would resize itself automatically to its contents. Operating System configuration files were loaded into the RAM disk on boot, greatly speeding operating system usage. Other files could be copied to the RAM disk like any standard device for quick modification and retrieval.
The Amiga OS also has support for a fixed-capacity recoverable RAM disk, which functions as a standard RAM disk, but can maintain its contents on restart. It was commonly called RAD disk and it can function as a start disk (with boot sector).
The main
modularisation technique in AmigaOS is based on
dynamically-loaded shared libraries, either stored as a file on disk with a "
.library" filename extension, or stored in the
Kickstart ROM. All libraries are accessed via an indirect
jump table, which is always stored in RAM. That way, every library function can be
patched or
hooked at run-time, even if the library is stored in ROM.
The most important library in AmigaOS is
exec.library, which can be considered a
microkernel, as well as a library. As well as
pre-emptive multitasking and access to other libraries, it provides high-level
inter-process communication via
message passing. (Other microkernels have had performance problems because of the need to copy messages between address spaces. Since the Amiga has only one address space, Exec message passing is quite efficient.) The only fixed memory address in the Amiga software (address 4) is a pointer to
exec.library, which programs must use to find other libraries. Exec was designed and implemented by
Carl Sassenrath.
Device drivers are also libraries, but they implement a standardised interface. Applications do not usually call devices directly as libraries, but use the
exec.library I/O functions to indirectly access them. Like libraries, devices are either files on disk (with the "
.device" extension), or stored in the Kickstart ROM.
The higher-level part of device and resource management is controlled by
handlers, which are not libraries, but
tasks, and communicate by passing messages.
One important type of handler is a
filesystem handler. The AmigaOS can make use of any filesystem for which a handler has been written, a possibility that has been exploited by programs like
CrossDOS and by a few "alternative" file systems to the standard
OFS and
FFS. These file systems allow one to add new features like
journaling or
file privileges, which aren't found in the standard operating system.
Handlers typically expose a
device name to the
DOS, which can be used to access the peripheral (if any) associated with the handler.
As an example of these concepts, the
SPEAK: handler can have text sent to it. The handler makes use of
translator.library, which converts text into
phonemes, then it writes the phonemes to
narrator.device, which translates the phonemes into intoned speech samples and itself uses
audio.device to play them through the Amiga's audio hardware.
Device names are
case insensitive (uppercase by convention) strings followed by a
colon. After the colon a
specifier can be added, which gives the handler additional information about
what is being accessed and
how. In the case of filesystem, the specifier usually consists of a
path to a file in the filesystem; for other handlers, specifiers usually set characteristics of the desired input/ouput channel (for the
SER: serial port driver, for example, the specifier will contain
bit rate,
start and stop bits, etc).
Filesystems expose
drive names as their device names. For example,
DF0: by default refers to the first floppy drive in the system, while
DH0: is the first hard drive.
Filesystems also expose
volume names, following the same syntax as device names: these identify the specific medium in the file system-managed drive. If
DF0: contains a disk named "Workbench", then
Workbench: will be a volume name that can be used to access files in
DF0:.
If one wanted to access a file named "Bar" located in directory "Foo" of the disk with name "Work" in drive
DF0:, one could write
DF0:Foo/Bar
or
Work:Foo/Bar
However, these are not completely equivalent, since when the latter form is used, the system knows that the wanted volume
is "Work" and not just any volume in
DF0:. Therefore, whenever a requested file on "Work" is being accessed without volume "Work" being present in any drive, it will say something to the effect of: Please insert volume Work in any drive
Programs often need to access files without knowing their physical location (either the drive or the volume): they only know the "logical path" of the file, i.e. whether the file is a library, a documentation file, a translation of the program's messages, etc.
This is solved in AmigaOS by the use of
assigns. An assign follows, again, the same syntax as a device name; however, it already points to a directory inside the filesystem. The place an assign points to can be changed at any time by the user. Standard assigns that are generally present in an AmigaOS system include
*
SYS:, which points to the boot drive's root directory; this is the only assign created automatically by the kickstart
*
LIBS:, pointing to a directory containing the system's libraries, usually SYS:Libs/
*
DEVS:, pointing to a directory containing the system's devices, usually SYS:Devs/
*
C:, pointing to a directory containing shell commands, usually SYS:C/
AmigaOS has spawned at least two "clone" operating systems over time.
AROS, or
Amiga Research Operating System is an attempt to clone the AmigaOS API in a portable open-source operating system. Although not binary compatible with AmigaOS (unless running on 68k), users have reported it to be highly source code compatible.
MorphOS is a PowerPC native operating system, originally created when the future of the Amiga looked uncertain. It provides binary compatibility with system-friendly AmigaOS applications. A version which runs on Classic Amigas with PPC accelerator cards has been released.
Although not strictly Amiga related, a fork of the
FreeBSD 4.8 release, called
DragonFly BSD, has been created by a former FreeBSD developer and Amiga programmer
Matt Dillon. DragonFly BSD aims to make the BSD core more like the Amiga architecturally, featuring a message-passing kernel and allowing for a very efficient and virtually
mutex-free SMP design.
AtheOS was inspired by AmigaOS, and originally intended to be a clone of AmigaOS.
Syllable is a fork of AtheOS, and includes some AmigaOS and
BeOS like qualities.
Some versions of AmigaOS included
copyright messages as
Easter eggs that required some trickery to access.
* In version 1.x, by holding down both Shift keys and both Alt keys and pressing the function keys F1 through F10, you could see copyright messages in the title bar. As an example, pressing F10 resulted in the message "Moral support:
Joe Pillow and the Dancing Fools". "Joe Pillow" was the name used to book a seat on a flight which was used to transport a prototype Amiga computer to a computer trade show [
6].
* In versions 2.x and 3.0, the secret message was accessed by repeatedly selecting the "About..." option from the Workbench menu, and leaving the resulting
dialog box open. When there were enough (approximately 20) dialog boxes open at the same time, the next one had a secret message instead of the normal one. In version 3.1 the secret message was openly integrated into the "About..." dialog box.
* The Amiga 1000 Kickstart floppy diskette master for AmigaDOS 1.0 was not erased prior to duplication, and contains the remnants of various source code and header text files on the disk.
*
AmigaOS versions*
AROS*
Comparison of operating systems*
Official AmigaOS 4 homepage*
AmigaOS homepage*
AmigaOS4 PreRelease Update 1 review*
AmigaOS4 PreRelease Update 4 first impressions*
AmigaOS Support homepage*
The Workbench Nostalgia Page - Very detailed information on all known versions of AmigaOS.
*
Amiga History Guide*
Reference Library*
Development site dedicated to Amiga systems*
On the Edge: The Spectacular Rise and Fall of Commodore (2005) Variant Press, ISBN 0973864907. - A book describing the creation of the AmigaOS.
*
Amiga user community portal*
AmigaOS4 Free Files Archive*
Aminet - Amiga OS all versions/MorphOS Free Files Archive
