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The Commodore Amiga

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Spanish for girlfriend, the Amiga computer has had a rocky history, rising to dominate the home computer market in the 1980s and early 1990s. The huge explosion in the PC market left the Amiga as a cult machine and left Commodore - its creators - going from one receiver to another. But now the Amiga shows the possibility of resurgence as a new computer standard and, bizarrely, a fridge.

Before the Beginning - the Code Explosion

Prior to computers such as the Amiga, Macintosh and PC-XT, which were the real forerunners to today's powerful machines, the home computer was a very different beast. With memory limited to 32 or 64 kilobytes (a fraction of the memory in a modern PC), any program that was to run in the computer used all of that equipment's resources. In other words, there was no multitasking, and certainly no graphical operating system running in the background. Programs were usually written in machine code (the native language of the processor) using an Assembler, although many computers had a built-in interpreter for one language (usually BASIC, though a few used Forth) so that programming could be accessible without an intimate knowledge of the hardware.

With the new explosion in power and capacity, there was no reason for computing to be so restrictive. Aside from the Operating System and some software that required complete use of the machine (such as games), programmers were free to do whatever they wanted because they didn't need to worry about controlling the whole computer - the OS could do that for them. As such there was an explosion of different methods of programming. Very few programmers stuck with machine language, partly because it was becoming unwieldy but also because in a multi-tasking environment every program has to be reentrant1, a feature that is provided by most high-level languages, but, in assembler, has to be coded manually. Many programmers elected C as their language of choice, a high-level language that also allows effective use of the hardware. Although BASIC remained in many guises, most programmers saw it as an oddity and refused flatly to develop software in it.

In the Beginning

The Amiga project was originally overseen by Atari, a company most famous for its computer games consoles. At the same time as the Amiga neared completion, Atari were working on their own machine, the ST. The two computers were very similar in specification, although the Amiga's speciality was in its graphics capabilities while the ST was designed for music. Atari thought that their own machine would fare better than the Amiga, so they looked for someone to carry on the project.

Commodore's own C64 computer had been very successful as a home machine, but they had no designs for a 'next generation' machine. It was Commodore who purchased the Amiga rights from Atari, which incensed many of their customers who believed that a new Commodore machine should have been legacy compatible with the C64 machine. Commodore on the other hand decided that the best way ahead would be a brand new start.

It turned out that Commodore were correct, and Atari were sadly very wrong. Although the Amiga was a very expensive computer when it was launched (at approximately $1000) in 1985, the slightly later and more compact A500 model sold by the tonne and outstripped the ST. The new computer of the late 1980s was the Amiga, which shared sales with the Macintosh from Apple, IBM XT (an early PC), and the dying throes of the microcomputers like the Sinclair Spectrum and Commodore's own C64.

Another contemporary machine was the Acorn Archimedes, the successor to Acorn's BBC Model B, whose ARM central unit was a full 32 bit processor. Unlike the MC68000 (see below) this was a RISC processor (Reduced Instruction Set Computer). This meant that it was faster but harder to program2. Although they were the staple computer in use in schools right up until the turn of the century, slow sales saw Acorn all but pull out of the home computing market and concentrate on specialist applications for their advanced processors.

The Hardware


The Amiga was one of a new generation of 16-bit computers3. This means that the registers in the processor were capable of handling 16 binary digits (1s and 0s) at a time rather than the 8 bits of earlier machines. The processor used was Motorola's 7MHz MC68000, the same as in Atari ST and Apple Macintosh units. Later Amigas featured enhanced versions of this chip - all numbered MC680x0 - and custom accelerator boards could be fitted to most of the models so that faster processors including the new PowerPC chips could be added.


As has already been mentioned, the major selling point of the Amiga was its graphics power. Unlike contemporary machines which used displays of 8 colours, the early Amiga including the A1000 and A500 models could animate a 32 colour screen in realtime (for use in games etc) and could display 4096 colours simultaneously using a trick known as HAM (Hold And Modify), where the colour of a pixel was set by comparing it with the pixel next to it. In this way the 4096 colours (which would require a 12 bits per pixel display on a PC) could be written with just six bits per pixel, halving the memory required.

Later models of the Amiga such as the A500+ and compact A600 featured the so-called Enhanced Chip Set which had an extra mode called Extra Half-Brite which could create a second version of the 32 colour palette with half the Value4 in one more bitplane.

The A1200 and A4000, the last of the 'classic' Amigas, had an Advanced Graphics Architecture (AGA). This could display 256 colours on a realtime display, and 16777216 simultaneously using the new HAM8 mode. This means that they were comparable to the Super VGA graphics available on today's PCs, but lack the speed or special hardware for helping with 3D graphics.

The bigger of the Amiga machines (including some with case modifications) could accept expansion boards similar to those available on the PC via an interface known as Zorro. One of the expansions available via this interface was known as the Video Toaster, which offered phenomenal acceleration for rendering three dimensional graphics displays. Although they were only available for the American TV display system (known as NTSC), the Video toaster still sold modestly in Europe. The hardware was used for rendering the computer generated special effects in the American science fiction programme Babylon 5.


One of the computers' drawbacks in later years was the sound chip, called Paula. While it had been innovative when the computer was first created, problems with legacy compatibility meant that it could not be upgraded as new machines were produced so that the A1200 had audio capabilities comparable with a contemporary £5 PC soundcard. The Paula chip had four channels (two in each stereo channel) capable of playing sounds simultaneously. The computer could take a sample and play it back at any frequency, which led to the explosion in Mod file music. Mods have a only few samples encoded in the files, but contain modules that tell the computer when and how to play each sample back, thus creating a tune.

Other Extensions

The Amiga was an infinitely expandable computer. As well as the accelerator boards already mentioned, the computers could be fitted with extra memory, hard drives, CD-ROMs, network hardware and any one of a number of different extensions. In fact Commodore's failed attempt at a console machine, the Amiga CD32 could be turned into a fully-fledged computer by the addition of a keyboard, mouse and hard drive.

Operating System

The Operating System that came with the Amiga, AmigaDOS, was originally developed by MetaComCo and then the project was continued by in-house developers at Commodore. It has a WIMP5 system called Workbench, which is similar to MacOS in design and execution. It also has a command-line interface that is very much like a Unix terminal. Early versions of Workbench included a version of Microsoft's Extended Basic, though this was dropped by version 2.0 (shipped with the Enhanced Chip Set computers) in favour of ARexx, a flexible scripting language. One of the system's biggest plus points is the ability to have more than one screen open on a monitor at any time, so that multitasking applications do not clutter up one desktop with lots of different windows. A similar system is currently employed by the KDE 2.0 interface for Linux, which allows up to 16 desktops that can be used simultaneously. The Windows equivalent Multiple Monitors is not really comparable, as it requires the use of two sets of graphics hardware including two different monitors.

An important feature of the Amiga is that a lot of the basic operating system is stored in ROM in the machine. This means that unlike a PC, software can be written that doesn't rely on the operating system being fully loaded, and can thus be faster and use less memory. This is important in the design of games software, where the programmers can 'bang the metal'6 and get the maximum available speed out of the computer.

The reason this is not possible in PC compatible computers is that the machines all have different hardware, so the Operating System is required to standardise the functions used to address these various configurations. If a program were written for one machine that used the hardware directly, it would almost certainly not work on another machine. The work around for this is to use driver software, which allows the programmer to write code in a standard format7 that is then converted into instructions for the hardware. This method increases the amount of code that must be executed by the processor, and thus slows operation of the program. In contrast to this, all Amigas have the same hardware (give or take a revision or two), so code written for one machine will work on another without a need for an additional layer of driver software.

The AmigaOS was designed as a pre-Unix system. However fully fledged Unix style operating systems are available for the machine, including BeOS, Linux and BSD.

Compact Disc Read-Only Memory

Commodore made two stabs at creating a computer with an integrated CD-ROM device, but both went the way of the Betamax8. The first, and perhaps the first ever computer with this technology, was the CDTV. This was in fact an A500esque computer with a CD-ROM drive and a remote control instead of a mouse and keyboard all in a sleek black box. The price tag was understandably a lot higher than for the regular machine, and the lack of volume and quality of CD specific software meant that it didn't take off.

The other attempt, in the wake of the AGA (Advanced Graphics Architecture, see above) based A1200 computer, was the CD32 games console. Although the machine just came with two joypads and looked a bit like a Sega Megadrive, it was in fact an almost completely functional A1200 plus an extra chip, which could be used as a full computer by means of an inexpensive expansion box. Unfortunately by the time this unit was released Commodore were already in serious financial trouble and this console came too late to stop them going bankrupt.

When is an Amiga not an Amiga?

When it's a Mac, PC, Spectrum, C64... the efficient hardware of the Amiga means that it is very capable of emulating another machine, that is interpreting the machine code of a different computer into native Amiga code and then handling the output as the other computer would. A novel system invented by Commodore was the Bridgeboard system. This had an almost complete PC on an expansion board for the Amiga, so that emulator software had access to a PC processor and other hardware making emulation faster. Although emulation is slower than using a real system, it may be the only option if your original computer is broken, or the software doesn't work. It is also better when testing out new software that could potentially cause serious damage to the machine, as it is cheaper to break an emulated computer than a real one. To this end the UAE9 is available for Workbench.

A similar system is the Siamese computer, which saw a brief period of life in the mid to late 1990s. This is not strictly an emulator, in fact it's an Amiga and a PC in the same box. The two can be switched between with a simple keypress, and can share hardware and information. This was a development of the 'piggyback' system where an Amiga could hijack a PC's hardware and use it for its own purposes. A similar system to the Siamese was developed by ARM (previously part of Acorn) for the RiscPC - Archimedes' successor - with a RiscPC and an IBM compatible sharing the same box. This was in fact a standard option for the Risc machine but was not widely used. The two computers could not run simultaneously, and using it involved finding and purchasing an Intel 80486 DX2 processor, which by the time of the RiscPC's release was already obsolete.

The Future...?

After Commodore went bankrupt, the Amiga name changed hands a few times. At one point it was owned by German technology retailers Escom, but they soon went into receivership while waiting for the ink on the contract to dry. The Amiga is now in the hands of another German company, called Amiga, and looks set for a relaunch. The company are touting a new standard called the AmigaOne, which they hope will find a niche in the professional computing market, probably as a server machine.

Another area of interest for the company is Digital Integration. This is the vision for the future where all of the equipment in your house is connected and can be run from a central computer. It would also mean that your utensils became more 'intelligent', so for instance your fridge could work out when you are low on milk and connect to your favourite online grocery store and order more. Amiga are still supporting the so-called 'Classic' Amigas to a limited extent, the most noticable evidence of this is the recent release of a new version of the Operating System.

1The program could be interrupted and resumed by the OS or other programs and could even be executed multiple times at the same time on the same computer without crashing the whole system. This is achieved by providing separated storage areas for each instance of the program.2As the RISC name suggests, these processors offer fewer and simpler instructions to the assembler programmer. These few instructions and the whole processor could thus be designed much more efficiently, so that the greater number of instructions needed for a given program is by far be outweighed by the performance of the system, at least in theory.3In fact, the computer's architecture was 16-bit, but the processors used 32-bit data internally.4One method of selecting colours is by Hue, Saturation and Value. The Hue selects the colour, the Saturation sets a sliding scale between gray (0%) and full colour (100%), and the Value sets the brightness.5Windows Icons Menus and Pointers.6A term meaning to write code for the hardware directly, rather than going via OS calls.7The Applications Programming Interface, or API.8A now obsolete standard for video recorders.9There is no general consensus as to what UAE stands for, except that we know it's an Amiga Emulator. Linux users claim it to be the Unix Amiga Emulator. The author says that during most of the program's development it didn't work, so he christened it the Unusable Amiga Emulator. Anyone who uses it for MS-DOS or Workbench systems says that it's the Universal Amiga Emulator.

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