Useful Notes / Amiga

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Commodore's 1985 follow-on to the Commodore 64, the Amiga was one of the first true "multimedia PCs", and featured several technologies that were years ahead of their time (including the 16/32-bit central processor). Executive Meddling and Misaimed Marketing kept the system from selling well in the USA, but elsewhere, the Amiga was far more popular and has a cult following to this day. (And when we say "cult", we mean it: Amigans are far more faithful to their platform than even Apple Macintosh fans, which is saying something after all it's been through.) At the time, its primary competition was the Atari ST.

The Amiga's heart was a set of extremely powerful custom integrated circuits designed by Jay Miner, who was also responsible for the custom graphics chips in the Atari 2600 and Atari 8-Bit Computers. These chips had names like "Fat Agnus" and included functions such as a "blitter", which allowed fast screen updates, and a "copper" that implemented scanline DMA (which eventually became a common trick on 16-bit consoles). The Amiga also included 4-channel, DMA-driven audio, which led to the development of the first MOD trackers, and the demoscene that surrounded them. Amiga could also "genlock" to NTSC or PAL video, making it very popular with TV production facilities; NewTek developed the Video Toaster, an early 3D animation and video editor system, to work with the Amiga's genlock and overlay capabilities. Many TV shows in the late 1980s and early 1990s used Amigas for computer screens and special effects, notably The Chart Show and Babylon 5. The development of anime fansubs in the late 1980s is also tied to the Amiga and its genlock capabilities, as it represented the first method of overlaying subtitles on video without high-end equipment unaffordable to the average user. Amigas were also used to power the Prevue Channel, a US TV channel that was just listings for all your local cable channels scrolling in a loop on the bottom half of the screen; the top half would be taken up by cable network's promos, cable company-created ads, and Prevue-produced segments about what to watch. A similar network called Sneak Prevue was launched in 1991, showing previews for pay-per-view movies and such. However, the Amigas were very error-prone and tended to crash frequently, leaving you with no guide or previews; by the late 90s, it began to suffer Network Decay, after TV Guide bought it and rebranded it as the TV Guide Channel; see that article for more. On the upside however, when TV Guide came along the Amigas were replaced with Windows PCs that definitely weren't as crash prone.

On top of this was AmigaOS, an operating system that had one of the earliest implementations of preemptive multitasking on a consumer PC (though without memory protection) and a relatively friendly GUI called "Workbench". The A1000 even had multiple desktops, which provided prior art that defeated a patent troll.

Despite being ahead of its time, the released AmigaOS is not the advanced operating system the Amiga engineers originally wanted; due to software development on the original CAOS falling behind schedule, Commodore instead opted to build upon a 68000 port of TRIPOS, which forms the AmigaDOS component of the final OS while still providing the promised preemptive multitasking capability.

Commodore eventually failed in 1994, and the Amiga, supported by fans, moved from company to company until settling down in 2000. AmigaOS was ported to the PowerPC and was sold on new hardware called the AmigaOne for a time in the early 2000s. AmigaOne is now selling a new computer, the AmigaOne X1000.

The Amiga Family:

Original Chip Set (OCS) Amigas, 1985-91
  • A1000 (1985): 68000 CPU, Workbench 1.0-1.3
  • A500 (1987): Lower-cost and improved version of the A1000, Workbench 1.2-3.1
    • Revision 6 boards and later often have an ECS Agnus and can use trapdoor Slow RAM as Chip RAM by changing JP 2 and cutting a trace near the trapdoor RAM pin header
  • A2000 (1987): High-end model based on the A500, with expansion slots and drive bays
    • A2000HD (1988): With a hard drive
    • A2500 (1989): With a 68020 or 68030 accelerator card, 32-bit Fast RAM, hard drive, and possibly a 'flickerfixer' card for VGA output.
    • A2500UX (1990): Similar to the A2500, but with the A2410 graphics card, and bundled with AMIX, the Amiga port of Unix.
    • Revision 6 boards also usually have an ECS Agnus and will run a full 1 MB of Chip RAM off the motherboard via jumper settings, no trace cutting necessary
  • CDTV (1991): Multimedia appliance based on the A500.

Enhanced Chip Set (ECS) Amigas, 1990-92
  • A3000 (1990): 68030 CPU, Workbench 2.04-3.9
    • A3000UX (1990): A3000 with AMIX
    • A3000T (1991): Tower model with more slots and bays
  • Late A2000 (1991): 68000 CPU, Workbench 2.04-3.1
  • A500+ (1991): 68000, Workbench 2.04-3.1
  • A600 (1992): 68000, Workbench 2.1-3.1

Advanced Graphics Architecture (AGA) Amigas, 1992-94
  • A1200 (1992): 68EC020 CPU, Workbench 3.0-3.9
  • A4000 (1992): High-end model, 68030 or 68040 CPU
  • CD32 (1993): Videogame console based on the A1200
  • A4000T (1994): Tower A4000 with more slots and bays, final Commodore Amiga

Post-Commodore Amigas
  • AmigaOne (2002): PowerPC G4 CPU, off the shelf graphics, Workbench 4
  • AmigaOne X1000 (2012): PWRficient PA6T CPU, Workbench 4.1

Other machines compatible with AmigaOS 4
  • Genesi Pegasos II (2004): PowerPC G4 CPU, AmigaOS 4 ported to it in 2009
  • ACube Sam440ep and Sam440ep-flex (2008): PowerPC 440 CPU
  • ACube Sam460ex (2010): PowerPC 440 CPU

Specifications:

Processors
  • CPU: Motorola 680x0 series (Commodore era) or PowerPC (post-Commodore)
  • GPU, OCS and ECS: "Agnus" (coprocessor/blitter, OCS) and "Denise" (sprites, video display, OCS) or "Fat Agnus" (coprocessor/blitter, ECS) and "Super Denise" (sprites, video display, ECS)
  • GPU, AGA: "Alice" (coprocessor/blitter) and "Lisa" (video display)
  • Sound: "Paula"

Memory
  • The Amiga was notorious for its split RAM banks, called "Chip RAM" and "Fast RAM". Chip RAM (graphics memory shared with the CPU) was used by Agnus/Alice and had to run at lock-step with the vertical refresh. Fast RAM (CPU-only system memory) could be accessed by the CPU at full speed. Then there was Slow RAM, the worst of both worlds.
  • OCS Amigas had 256K (A1000), 512K (A500, A2000), or 1MB (late A2000, CDTV) Chip RAM, 512K Slow RAM (A500 via internal REU, A2000) and up to 8MB Fast RAM.
  • ECS Amigas had 1-2MB Chip RAM, up to 8MB (A500+, A600) or more (A3000) Fast RAM
  • AGA Amigas had 2MB Chip RAM, up to 16MB (A1200) or more (A4000) Fast RAM

Display: OCS/ECS
  • 4096 color palette
  • Nominal resolution from 320x200 to 640x400 NTSC, 320x256 to 640x512 PAL
  • Overscan up to 736x482 NTSC, 736x576 PAL
  • ECS: 1280x400 with 4 colors out of 64
  • ECS supports both 50Hz and 60Hz refresh rates, OCS is either PAL or NTSC only depending on region.
  • 32 independent colors in 320xX, plus an "Extra Half-Brite" mode that adds 32 more colors, half as bright as the first 32
  • 16 colors in 640xX
  • Hold And Modify mode in 320xX: all 4096 colors on screen
  • Palette swaps on scanline interrupt
  • 8 hardware sprites
  • Coprocessor and blitter for hardware scrolling and sprite manipulation

Display: AGA
  • 16 million color palette
  • All OCS/ECS resolutions, plus 640x480, 800x600 and 1024x768
  • 256 colors at any resolution
  • HAM-8 mode with 262,144 colors on screen

Sound
  • Four DMA-driven eight-bit PCM channels, software mixable into two fourteen-bit PCM. For a time in the late 1980s and early 1990s, the Amiga was as good as it got when it came to sample-based sound, unless you had the money to buy a professional sampler/workstation.

Notes for those who might want to buy hardware:

The Amiga gaming experience is surprisingly console-like, since most games boot directly from floppy disks. That said, floppies are slow and often need to be swapped on bigger games, so hard drive installs are recommended wherever possible.

For games that do not include their own installers from within the Workbench environment, you can use WHDLoad, though do note that several games require at least 1 MB of Chip RAM to use it and will not work with systems with only 512 KB of Chip RAM. Some non-AGA titles may even require more than 1 MB, for which the only solution for A500 and A2000 owners is to track down a rare and often very expensive upgrade like the DKB MegAChip 500/2000.

Apart from the CD32, the main game-playing Amigas are the 500 and the 1200. Most A500 games will run on both, though for older or badly made titles, a piece of software called relokick may be required.

If you're using a 32-bit machine, you may also have to disable the CPU's instruction and data caches for a game to run properly, as self-modifying code (software that overwrote its own instructions with new instructions for performance reasons) was a popular trick at the time, but if not implemented in a way that took the 32 bit 680x0 chips' caches into account would lead to the code in the cache not matching the code in RAM, resulting in hard crashes. Kickstart 3 onwards had an early boot menu that gave you the option of disabling CPU caches if present. In the early days, game developers were encouraged to bypass the OS and access the hardware directly, optimizing performance at the expense of forwards compatibility. The 'correct' '80s Amiga is an A500 with the OCS and Workbench 1.2 or 1.3. You will also need some more RAM, preferably the A501 512k "trapdoor" card or one of its popular third-party clones.

The A501 Slow RAM expansion for the A500, and the A500+, A2000, A3000, and A4000 have a NiCd battery to back up the clock. With age, these batteries leak acid onto the motherboard, destroying any nearby traces or pins. If you're interested in an Amiga on eBay, demand to see a picture of the battery before you buy it. If there are signs of battery leakage and corrosion, find another one, or try to negotiate a lower price and repair the traces and sockets yourself if you're handy with a soldering iron and multimeter.

If you're a hardware maniac, however, the A1200 is the computer for you (unless you're willing and able to fork over the money for an AmigaOne-series machine). It can be upgraded more than any other Commodore-era "classic" Amiga model, allowing you to install PCI cards (even graphics) with a busboard expansion, add a PowerPC processor, and even make it play nicely with the Wi-Fi network you have at home.

As of 2016, a new FPGA accelerator board known as the Apollo Vampire hit the market, originally for the A600, and later, the A500 (which also works in the A1000 and A2000, with CPU slot adapters being made for the A2000 specifically to use the Vampire). For roughly the same price as an A1200, you get a 68080 CPU core that trounces even the 68060 in performance, 128 MB of RAM (which, by Amiga standards, is ludicrous), a SAGA (Super AGA) custom chipset reimplementation with retargetable graphics (RTG) and HDMI output, the ability to add cheap Ethernet modules for networking, and on the A500 version, an IDE/Parallel ATA controller and interface. On top of that, a standalone version for the V4 generation of the Vampire is under development, with no reliance on existing Amiga motherboards.

This upgrade alone, while unquestionably expensive (300 EUR/370 USD at time of writing), puts the OCS/ECS-era Amiga models on a level above and beyond the AGA ones, particularly those lacking 68060 accelerators and RTG cards that would normally sell for thousands of dollars by themselves.

There's also Amiga Forever, which is a collection (sold either as an ISO9660 image or a physical CD) containing system ROM images and OS disk images for all Commodore-era hardware and OS versions (that is, up to 3.1), for use in an emulator (such as WinUAE, E-UAE, or UAE).

There is also now an OS for the Raspberry Pi called Amibian that, when fed the official Kickstart ROM files, will allow emulation of a large number of Amiga machines from an SD card.

Magazines:

Games:

PowerPC-only games are marked with an asterisk.

Original Titles

Ported, Concurrently Developed, or Original Platform Unclear


Alternative Title(s): Commodore Amiga, CD 32

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