Amiga 500

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Commodore Amiga 500

An Amiga 500 computer system, with 1084S RGB monitor and second A1010 floppy disk drive
Type	Home computer
Release date	1987
Discontinued	1991
Media	880 KB floppy disks
Operating system	AmigaOS 1.2~1.3
CPU	Motorola 68000 @ 7.16 MHz 7.09 MHz (PAL)
Memory	512 KB (9.5 MB maximum)

The Amiga 500, also known as the A500, was the first “low-end” Commodore Amiga 16/32-bit multimedia home/personal computer. It was announced at the winter Consumer Electronics Show in January 1987, at the same time as the high-end Amiga 2000, and competed directly against the Atari 520ST. The A500 was released in mid 1987 at the price of 595.95 USD without monitor.

The original A500 proved to be Commodore’s best-selling Amiga model, enjoying particular success in Europe.^[1] Although popular with hobbyists, arguably its most widespread use was as a gaming machine, where its advanced graphics and sound were of significant benefit.

Releases

In October 1989, the A500 was bundled with the Batman Pack, which was sold in the United Kingdom.^[2]

In late 1991, an enhanced model known as the A500 Plus replaced the standard A500 in some markets.

The A500 series was discontinued altogether in mid-1992. The similarly-specified and priced Amiga 600 was marketed as its replacement, although this new machine had originally been intended as a much cheaper budget model, the A300. In late 1992, Commodore released the “next-generation” Amiga 1200, a machine closer in concept to the original A500, but featuring significant technical improvements. Despite this, neither the A1200 nor the A600 replicated the commercial success of its predecessor as, by this time, the market was definitively shifting from the home computer platforms of the past to commodity Wintel PCs and the new low-cost Macintosh LC and IIsi models.

Technical description

Like its predecessor, the Amiga 500 uses a Motorola 68000 microprocessor running at 7.15909 MHz in the NTSC version or 7.09379 MHz in the PAL version. While the 68000 is a 32-bit chip internally, it has a 16-bit data bus and 24-bit address bus, providing a maximum of 16 MB address space. Also like the Amiga 1000, the 500 uses the OCS chipset. Graphics can be of arbitrary dimensions, resolution and colour depth, even on the same screen. Without using overscan, the graphics can be 320 or 640 pixels wide by 200 (NTSC standard) /256 (PAL standard) or 400 (NTSC interlace)/512 (PAL interlace mode) pixels tall. Overscan mode enabled 700 x 600 resolution in PAL machines.^[3][4] Planar graphics are used, with up to 5 bitplanes (4 in hires), allowing 2, 4, 8, 16 and 32 colour screens, from a palette of 4096 colours. Two special graphics modes where also included: Extra HalfBrite, which used a 6th bitplane as a mask that halved the brightness of any colour seen, and Hold And Modify (HAM), which allowed all 4096 colours on screen at once. Later revisions of the chipset made PAL/NTSC mode switchable in software. Sound is 4 hardware-mixed channels of 8-bit sound at up to 28 kHz. The hardware channels had independent volumes (65 levels) and sampling rates, and mixed down to two fully left and fully right stereo outputs. A software controllable low-pass audio filter is also included. The machine came standard with 512 KB of Chip RAM and AmigaOS 1.2 or 1.3. One double-density floppy disk drive is included, which is completely programmable and thus can read 720 KB IBM PC disks, 880 KB standard Amiga disks, and up to 984 KB with custom formatting (such as Klaus Deppich’s diskspare.device). Breaking with the Amiga 1000, and in keeping with the home computer tradition established by the VIC-20 and C64, the A500 had its keyboard integrated with the CPU unit, although the floppy disk drive is also integrated, unlike the 8-bit models. The 500 used the standard Amiga two-button mouse.

Despite the lack of Amiga 2000-compatible internal expansion slots, there are many ports and expansion options. There are two Atari 2600 DB9M sockets for joysticks or mice, stereo audio (RCA connectors 1V p-p). There is a floppy drive port for daisy-chaining up to 3 extra floppy disk drives via an DB23F connector.^[5]. The then-standard RS-232 serial port (DB25M) and Centronics parallel port (DB25F) is also included. The power supply is (+5 V , +/-12 V).^[6] The Amiga 500's graphics are output in analogue RGB 50 Hz PAL and 60 Hz NTSC video output, provided on an Amiga-specific DB23M video connector. It can drive video with 15,75 kHz HSync for standard Amiga video modes but this is not compatible with most VGA monitors. A Multisync monitor is required for some higher resolutions. This connection can also be genlocked to an external video signal. An RF adapter was bundled with the machine to provide output on regular televisions. Monochrome video is available via an RCA connector. There is a Zorro II bus expansion the left side behind a plastic cover and a trapdoor slot under the machine, for RAM expansion and real-time clock.

Somewhat unusually for a budget machine, all chips are socketed rather than through-hole soldered so if the casing is opened up (voiding the warranty), they can be replaced by hand. The CPU can be upgraded to a 68010 directly or to a 68020, 68030 or 68040 via the side expansion slot. The Chip RAM can be upgraded to 1 MB directly on the motherboard, provided a Fat Agnus chip is also installed to support it. In fact, all the custom chips can be upgraded to the ECS chipset. 512 KB of “Slow RAM” or “Trapdoor RAM” can be added via the trapdoor expansion. Such upgrades usually also included a battery-backed clock. If further expansion is desired, up to 8 MB of “Fast RAM” can be added via the side expansion slot. Hard drive and other peripherals can also be added via the side expansion slot. So many options vying for one expansion slot can have made for difficult choices, but several companies provided combined CPU, memory and hard drive upgrades, or provided a pass-through expansion slot so multiple devices can be chained. Expansions are configured automatically by AutoConfig software, so multiple pieces of hardware did not conflict with each other. The Amiga is plug and play.

Technical specifications

• OCS chipset. Later revisions of the chipset made PAL/NTSC mode switchable in software.
  • Graphics can be of arbitrary dimensions, resolution and colour depth, even on the same screen.
  • Without using overscan, the graphics can be 320 or 640 pixels wide by 200/256 or 400/512 pixels tall.
  • Planar graphics are used, with up to 5 bitplanes (4 in hires), allowing 2, 4, 8, 16 and 32 colour screens, from a palette of 4096 colours. Two special graphics modes where also included: Extra HalfBrite, which used a 6th bitplane as a mask that halved the brightness of any colour seen, and Hold And Modify (HAM), which allowed all 4096 colours on screen at once.
  • Rhett Anderson developed the so called Sliced HAM or SHM mode, which was a standard 32-color mode, but allowed each video scan line to have its own, independent 32-color palette. This was possible because of a special co-processor that could reprogram the color palette registers at the beginning of each scan line. The advantage of SHM files was the ability to display all 4096 colors while eliminating the color blur of HAM compression.
  • Sound is 4 hardware-mixed channels of 8-bit sound at up to 28 kHz. The hardware channels had independent volumes (65 levels) and sampling rates, and mixed down to two fully left and fully right stereo outputs. A software controllable low-pass audio filter is also included.
• 512 KB of Chip RAM.
• AmigaOS 1.2 or 1.3
• One double-density floppy disk drive is included, which is completely programmable and thus can read 720 KB IBM PC disks, 880 KB standard Amiga disks, and up to 984 KB with custom formatting (such as Klaus Deppich’s diskspare.device).
• Built in keyboard.
• A two-button mouse is included.

Graphics

• PAL mode: 320 x 256, 640 x 256, 640 x 512 (interlace), 700 x 600 in overscan. Max 6 bpp.^[3][4]
• NTSC mode: 320 x 200, 640 x 200, 640 x 400 (interlace).

Connectors

• Two DB9M sockets for joysticks or mice (as popularized by the Atari 2600).
• Stereo audio (RCA connectors 1V p-p).
• A floppy drive port (DB23F), for daisy-chaining up to 3 extra floppy disk drives via an DB23F connector.^[5]
• A standard RS-232 serial port (DB25M).
• A parallel port (DB25F).
• Power inlet (+5 V , +/-12 V).^[6]
• Analogue RGB 50 Hz PAL and 60 Hz NTSC video output, provided on an Amiga-specific DB23M video connector. Can drive video with 15, 75 kHz HSync for standard Amiga video modes. This is not compatible with most VGA monitors. A Multisync monitor is required for some higher resolutions. This connection can also be genlocked to an external video signal. An RF adapter (A520) was bundled with the machine to provide output on regular televisions. A digital 16 colour Red-Green-Blue-Intensity signal is available too on the same connector.
• Monochrome video via an RCA connector.
• Zorro II bus expansion the left side behind a plastic cover.
• Trapdoor slot under the machine, for RAM expansion and real-time clock.

Expansions

• Expansion ports are limited to a side expansion port and a trapdoor expansion on the underside of the machine. The casing can also be opened up (voiding the warranty), all chips are socketed rather than through-hole soldered, so they can be replaced by hand.
• The CPU can be upgraded to a 68010 directly or to a 68020, 68030 or 68040 via the side expansion slot.
• The Chip RAM can be upgraded to 1 MB directly on the motherboard, provided a Fat Agnus chip is also installed to support it.
• Likewise, all the custom chips can be upgraded to the ECS chipset.
• 512 KB of “Slow RAM” or “Trapdoor RAM” can be added via the trapdoor expansion. Such upgrades usually also included a battery-backed clock.
• Up to 8 MB of “Fast RAM” can be added via the side expansion slot.
• Hard drive and other peripherals can be added via the side expansion slot.
• Several companies provided combined CPU, memory and hard drive upgrades, or provided chainable expansions, as there is only one side expansion slot.
• Expansions are configured automatically by AutoConfig software, so multiple pieces of hardware did not conflict with each other.

Notable uses

• Digital hardcore group EC8OR recorded their premier title album using only an Amiga 500 and a microphone.

See also

• Amiga models and variants
• Minimig

References

External links

• amigahardware.mariomisic.de Amiga 500 photos

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