Commodore Amiga | Code Like It's 198x

Early in 1984 a small Silicon Valley company called Amiga showed journalists a computer that was still a collection of circuit boards. BYTE described it the following summer: a Sage 68000 machine acting as the processor, wired to “big steel boxes” that did the graphics and sound, and a ball bouncing across the screen while the sound “shifted from the right speaker to the left”. “Everyone wondered if Amiga could really reduce all the power in the prototypes to silicon chips.” Eighteen months later the steel boxes had become three custom chips, and Commodore unveiled the result as the Amiga 1000 at New York’s Lincoln Center on 23 July 1985. At the launch Andy Warhol used a video digitiser to “paint” a portrait of Blondie’s Debbie Harry on it.

BYTE contrasted it with the Macintosh, which “does almost everything in software”. The Amiga surrounded its Motorola 68000 with chips that worked on their own. Agnus fetched memory for everything else and contained the blitter and the copper. Denise turned bitplanes and sprites into a picture. Paula played four channels of sampled sound and handled the disk, the serial port and interrupts. Over it ran an operating system that shared the processor between programs preemptively. When AmigaWorld looked back in 1995, it noted that Windows 3.1 and Macintosh System 7 still used “less-efficient, cooperative multitasking”.

The Amiga 1000 cost $1,295 without a monitor. The A500 of 1987 put the same chipset into a keyboard case at a price European households would pay, and AmigaWorld later called it “the most popular Amiga model”. In March 1988 CRASH counted only about 130,000 Amigas and Atari STs in Britain, against four million Spectrums. By mid-1992 Amiga Format put the UK’s Amigas at 1.2 million, most of them A500s. Two years later Commodore collapsed, but Amigas went on being made under new owners until 1996.

Fast facts

Launch: Amiga 1000, 23 July 1985 in New York, at $1,295. British buyers saw it at the Commodore Show at the Novotel in Hammersmith in May 1986, at about £1,500.
CPU: Motorola 68000 at 7.09379 MHz (PAL) or 7.15909 MHz (NTSC), a quarter of a 28.37516 or 28.63636 MHz crystal. One chip-memory cycle takes two CPU clocks (about 280 ns), and one low-resolution pixel lasts one CPU clock. Later models used the 68020, 68030 and 68040.
Custom chips: Agnus, Denise and Paula. The original chip set (OCS) was followed by the Enhanced Chip Set (ECS) in later A500s and A2000s and the A3000 of 1990, and by the AGA chip set (Alice, Lisa and Paula) in the A4000 and A1200 of 1992.
Graphics: planar bitmaps from 32 colour registers, each chosen from a palette of 4,096. PAL low resolution is 320×256 in up to 32 colours, and high resolution is 640×256 (640×512 interlaced) in up to 16. A sixth low-resolution bitplane buys a mode rather than more free colours: Extra Half-Brite adds a half-brightness copy of the 32 colours, and hold-and-modify (HAM) shows all 4,096 at once. There are eight hardware sprites, each 16 pixels wide. AGA raised the palette to 16.8 million colours, the colour count to 256 and HAM to 262,144 colours.
Sound: four channels, each with an 8-bit digital-to-analogue converter, its own sample rate and a volume from 0 to 64, fed by DMA. Two channels go to each side of the stereo output.
RAM: 256K on the A1000 and 512K on the A500. Chip memory is shared with the custom chips; Fast memory is outside their reach, so the chips can never steal the processor’s cycles there.
Operating system: Exec’s preemptive multitasking kernel, AmigaDOS, the Intuition window system and the Workbench desktop. The A1000 loaded its Kickstart code from a floppy disk at every power-on; later models kept it in ROM. Version 2.0 arrived with the A3000 in 1990 and version 3 with the A1200 and A4000 in 1992.
Storage: 3.5-inch double-sided floppy, 880K per disk: 80 tracks a side of eleven 512-byte sectors. Disk DMA reads a whole track of raw MFM data into memory in one revolution, and software decodes it.

From Lorraine to Lincoln Center

Amiga began in 1982 as Hi-Toro, a start-up meant to build a games machine. Jay Miner, who had designed chips for Atari’s VCS and 800, led the hardware, and Dave Morse ran the company. The prototype was code-named Lorraine, after Morse’s wife, Commodore User reported in November 1984. According to R.J. Mical’s account, as retold by Amiga Computing in 1988, the company built joysticks and a stand-on “Joyboard” as cover while the real work went on. Mical came from the arcade maker Williams to write software.

The team’s names run through Commodore’s own manuals. Carl Sassenrath wrote Exec, the multitasking kernel. Dale Luck wrote the graphics and layers libraries. R.J. Mical designed and first coded Intuition. Dave Needle is among the engineers the 1986 Hardware Reference Manual thanks. AmigaDOS came from outside: it was based on TRIPOS, a multitasking operating system first written for minicomputers at Cambridge University, and adapted for the Amiga by Metacomco.

For the Consumer Electronics Show in January 1984 the custom chips still existed only as large circuit boards. Amiga Computing’s account says each was so fragile that it took a seat of its own on the plane, and that the team worked the stand by day and wrote programs at night, including the first version of the Boing demo. Dale Luck, one of its programmers, later recalled that at that show the ball only bounced up and down and made no sound; by the Summer CES in June 1984 it moved from side to side, and BYTE remembered the demonstrations of early 1984 for the way its sound moved from one speaker to the other. The show impressed people but the games market was collapsing, and the money ran out. The same account says Jack Tramiel’s Atari lent Amiga half a million dollars while negotiating a takeover, and that Commodore then raised its offer from $4 to $4.25 a share and Morse signed. Commodore bought Amiga in 1984 and raised the base machine from 64K of memory to 256K.

The Amiga 1000 shipped in September 1985. The designers’ signatures were moulded into the inside of its case, and Amiga Format noted that one of the signatories was Mitchy, Jay Miner’s dog. In Britain, Commodore first said the machine would not arrive until June 1986. It reached British buyers in May 1986 at a price that, as Commodore User put it, placed it in “the fiercely competitive small business micro market”. That July Commodore User reported a Guardian estimate that only 50,000 Amigas had been sold worldwide.

The machine that programs itself

The Amiga’s central idea is delegation: most of the interesting work happens on chips that are not the CPU.

The copper is a co-processor with three instructions. MOVE writes a value to a chip register, WAIT waits for the video beam to reach a position, and SKIP jumps over the next instruction if the beam is already past one. With those three it can change the palette on any scanline, split the screen into bands with different resolutions and colour depths, or reload bitplane pointers mid-frame. On the Commodore 64 the same effects take a raster interrupt and CPU time. On the Amiga the copper runs its list every frame while the 68000 does something else.

The blitter copies rectangles of memory through a barrel shifter. It reads up to three sources, combines them in “one of 256 different possible ways” chosen by an eight-bit minterm, and writes the result. It also draws lines, at about a million dots a second according to the manual, and fills areas. Scrolling, masked sprite drawing (“cookie-cutting”) and polygon fill are all blitter jobs, and much of a demo’s or game’s frame is spent keeping it fed.

The catch is the bus, and the Hardware Reference Manual prices it exactly. Disk, audio, display and sprite DMA have the highest priority, because a missed slot means lost data, noise or a broken picture. On a standard-width display, the visible part of each scanline is 160 memory slots long.

In low resolution, four bitplanes or fewer leave the 68000 its alternate memory cycles and cost nothing. Past four, bitplane DMA starts taking cycles the processor would have had. At six planes it uses six slots in every eight, which in the manual’s words “steals 50 percent of the open slots that the processor might have used if there were only four bitplanes displayed.” A six-plane Extra Half-Brite or HAM screen costs the processor half its chip-memory access during the display.

In high resolution each plane fetches 40 words a line rather than 20, and the manual does that sum too: four planes take all 160 slots. That “effectively locks out the 68000 (as well as the blitter or Copper) from any memory access during the display, except during horizontal and vertical blanking.” A 16-colour high-resolution screen stops the co-processors that define the machine for the whole visible frame.

That arithmetic decides how many bitplanes a program can afford, and it is why Fast memory matters: the chips cannot touch it, so code running there never waits for them. Programming the Amiga well means scheduling work across several processors that share one bus.

Programming it

Commodore shipped the A1000 with AmigaBASIC, written by Microsoft, and documented the operating system’s libraries for programs written in C or assembly language. The Hardware Reference Manual set the rule for going further: a program may drive the chips directly only if it “has full control of the system” or has been granted exclusive access by the operating system. Games took the first route so often that a reader wrote to Amiga Shopper in 1993 that “most new games hit the hardware”. The magazine had told another reader that, short of “an action packed scrolling arcade game”, there was little excuse for it any more, and it warned that because there was no hardware guide to the AGA chips, 256-colour screens had to go through the operating system.

Two BASICs gave many people their start. AMOS was written for the Amiga “from scratch” by François Lionet, who had written STOS for the Atari ST, and published by Mandarin Software in 1990. Previewing it that May, Amiga Computing counted “more than 400 different functions and commands”, with bobs, sprites and music built in, and watched its logos and sprites scroll “almost as greasily and quickly as in any machine code demo”. Blitz Basic 2 came from New Zealand, from Mark Sibly and Acid Software, and compiled to machine code. Amiga Format put a working version on the cover disk of issue 52 in 1993, and pointed out that Vision Software’s four-player racing game Skidmarks “was all written in Blitz Basic 2.”

Why it mattered

Sampled sound as standard. Four channels of 8-bit samples meant recorded instruments and voices from the first model. They also made the Amiga the home of the tracker. By June 1990 Amiga Computing reckoned that “99.999 per cent” of game and demo tunes “are written with a utility called SoundTracker, or one of its many derivatives”. Soundtracker was Karsten Obarski’s commercial program, copied and modified by crackers who put their own names in it, and its song files became the MOD format. See tracker music.
Creative work on a home budget. In early 1986 Commodore User reported that Electronic Arts’ Deluxe Paint, at $129, was “the only package that really taps” the Amiga’s graphics. The A2000’s slots made it the host for NewTek’s Video Toaster. In 1995 AmigaWorld’s list of television series made with Amigas included Babylon 5 and seaQuest DSV.
Games with a different look. Copper-driven colour gradients, parallax layers and 32-colour art gave Amiga games a recognisable style (see Amiga art style). Amiga Format gave Psygnosis’s Shadow of the Beast only 78% in 1989 while calling it “outrageously good-looking”: “The animation, the sprites, the backgrounds and the parallax scrolling are all superb.”
The British market. From a niche shared with the ST in 1988, the Amiga passed a million British homes within four years. A 1992 Amiga Format special claimed that by 1990 the A500 was “the best-selling computer in the UK”. Amiga Computing put the number of Amigas in Britain at about 1.5 million in 1994, and AmigaWorld estimated “nearly five million” worldwide that year. These are magazine estimates, not audited figures.
The demoscene. The Amiga became one of the main machines of the demoscene. In 1990 Amiga Computing described Obarski’s editor as famous “among both crackers and demo writers”.

Models

A1000 (1985): the original, with a keyboard that slid into a “garage” under the case when not in use. It loaded Kickstart from disk.
A500 (1987): the chipset in a keyboard case with Kickstart in ROM. Commodore User reported its UK launch at the Commodore Show in June 1987, when dealers offered it “from £499 + VAT”. By that December a mail-order advertisement in the same magazine offered it at £399. AmigaWorld later called it “the most popular Amiga model”.
A2000 (1987): a desktop case with Zorro expansion slots, redesigned by Commodore’s German engineers after the original Los Gatos design was rejected. UK dealers listed it “from £1095.00 + VAT”.
A3000 (1990): a 68030, ECS and Workbench 2.0, aimed at workstation buyers.
A500 Plus (1991): Kickstart 2.04, ECS and 1MB of memory. Amiga Format recalled that it “was launched under a wave of controversy”, and it was replaced within a year.
A600 (1992): a smaller case with no numeric keypad, a PCMCIA slot and an internal IDE connector, on sale in the UK from May 1992 at £399. AmigaWorld judged that, planned as a cheaper complement to the A500, it “ended up costing more and doing less”.
A4000 (1992): the 68040 and the AGA chip set, released in the UK at £2,099. A cheaper 68030 version was unveiled at CeBIT in 1993.
A1200 (1992): AGA, a 68EC020 at 14.19 MHz and 2MB of chip memory in a keyboard case. Its UK launch in London on 21 October 1992 set the price at £399.99, and Amiga Format reported that only 30,000 would reach Britain before Christmas.
CD32 (1993): an AGA games console with a CD drive, at £299.99 in the UK. Commodore collapsed the following spring.

After Commodore

Commodore announced large losses in March 1994, and the New York Stock Exchange suspended trading in its shares. On 29 April 1994 Commodore International announced that it was transferring its assets to trustees for its creditors and placing its main subsidiary, Commodore Electronics, into voluntary liquidation. Its Philippines factory closed. Commodore UK stayed solvent, kept selling stock from a European pool, and bid for the business itself.

The German PC maker Escom won the auction in April 1995 for US$10 million. Its Amiga Technologies subsidiary restarted A1200 production, and the first new machine came off the line at Bordeaux on 11 September 1995. In 1996 Escom filed for bankruptcy and agreed to sell Amiga Technologies to ViScorp. The period press records no later production of the classic machines.

Modern legacy

Emulators such as WinUAE and FS-UAE run Amiga software on modern computers, and MiSTer FPGA cores recreate the chipset in programmable logic.

Sources

BYTE, August 1985: editorial with the $1,295 price (p. 6); the early-1984 prototypes shown to journalists (p. 81); “In Brief” specifications (p. 84); the comparison with the Macintosh.
AmigaWorld, November/December 1985, p. 48: Warhol’s digitised portrait of Deborah Harry at the Lincoln Center launch. AmigaWorld, January 1995: launch and shipping dates (p. 13); preemptive multitasking and the Windows 3.1 and System 7 comparison, the keyboard “garage”, the A2000’s German redesign and the list of television series (p. 14); notes on the A500, A600 and CD32 (p. 15). AmigaWorld, October 1994, p. 2: “nearly five million Amigas” worldwide.
Amiga Hardware Reference Manual, 3rd edition (Commodore-Amiga, Addison-Wesley, 1991): clock speeds (p. 2); display modes, palette, sprites, blitter and audio overview (pp. 3-4); Chip and Fast memory, Agnus versions and ECS (pp. 4-5); floppy format (p. 5); the rule on direct hardware access (p. 8); the copper’s three instructions (p. 20); bitplanes, HAM and Extra Half-Brite (pp. 86-90); audio converters and volume (p. 137); blitter minterms (p. 174); DMA priorities and time slots (pp. 193-197); disk controller (p. 241); Appendix F, crystal frequencies; glossary entries for Agnus and Paula.
Amiga Hardware Reference Manual (Commodore, Addison-Wesley, 1986): acknowledgements to Bill Kolb, Dave Needle, Lee Ho and Dale Luck.
Amiga ROM Kernel Manual, volume 1 (Commodore-Amiga, 1985), “Tasks”, p. 1-12: Exec’s preemptive, time-sliced scheduling.
Introduction to the Amiga 1000 (Commodore, 1986), p. 3-3: starting up from the Kickstart disk. Introduction to the Amiga 500 (Commodore, 1987), specifications: Kickstart in ROM. Amiga 1000 software sheet (Commodore-Amiga, 1985): Amiga BASIC by Microsoft.
The Kickstart Guide to the Amiga (Ariadne Software, 1987), p. 9: Exec by Carl Sassenrath, graphics and layers by Dale Luck, Intuition by R.J. Mical.
Commodore User, November 1984, p. 46: the Lorraine code name. February 1986, p. 7: UK arrival delayed to June; Deluxe Paint at $129. July 1986, p. 6: Commodore’s losses, the small-business pricing and the Guardian’s 50,000 figure. May 1987, p. 14: A500 launch at the Commodore Show. July 1987: dealer advertisement, A500 “from £499 + VAT”, A2000 “from £1095.00 + VAT”. December 1987: mail-order advertisement, A500 at £399.
Your Commodore, June 1986, p. 13: the Commodore Show at the Novotel, Hammersmith, “featuring the UK launch of the fabulous Amiga”. CRASH, issue 30, July 1986, p. 11: the launch of “the £1,500 version”. CRASH, issue 50, March 1988, p. 32: “about 130,000 Amigas and STs in the country”.
Jimmy Maher, The Future Was Here: The Commodore Amiga (MIT Press, 2012), pp. 17–18: Dale Luck’s recollection of the Boing demo at Winter CES 1984, and its sound and sideways motion by Summer CES in June 1984.
Amiga Computing, December 1988, pp. 24-26: the Amiga story as R.J. Mical used to tell it (Hi-Toro, the joysticks, CES 1984, the Boing demo, Atari’s loan and Commodore’s offer, TRIPOS and Metacomco, the 256K base machine). May 1990, p. 64: AMOS preview. June 1990, p. 99: SoundTracker. July 1990: A3000 launch review and Workbench 2.0. November 1990: SoundTracker “famous among both crackers and demo writers”. June 1993: the A4000/030 at CeBIT. November 1993: CD32 at £299.99. July 1994: about 1.5 million Amigas in Britain. December 1995: A1200 production restarts at Bordeaux. October 1996: Escom files for bankruptcy.
Amiga Format, issue 4, November 1989, pp. 42-43: Shadow of the Beast review. Amiga Format Special 4 (1992): the A500’s UK sales claim and the A600’s reception and price. Issue 36, July 1992, p. 19: 1.2 million Amigas in the UK, the A500 Plus’s controversial launch and the A600’s arrival in May. Issue 41, December 1992, pp. 22-24: the A1200 launch and AGA; A4000 price and Kickstart 3 in the same issue. Amiga Format Special 7 (1993): Blitz Basic 2 from New Zealand and Skidmarks. Blitz User (Acid Software), issue 1, June 1992: “Blitz author Mark Sibly”; issue 3, March 1993: Acid Software’s Auckland office. Issue 72, June 1995: the Escom auction, Commodore UK’s position, and the A1000 case signatures. Issue 130, December 1999: Mitchy the dog.
Amiga Shopper, issue 18, October 1992, and issue 32, December 1993: readers’ letters on hitting the hardware, and the advice that AGA’s 256-colour modes had to go through the operating system. Issue 39, July 1994, p. 4: Commodore UK trading on, the Philippines factory and the European stock pool.
Amazing Computing, July 1994, p. 55: Commodore’s announcement of 29 April 1994 and the events of March 1994.