Amiga 500

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Commodore Amiga 500
An Amiga 500 computer system, with 1084S RGB monitor and second A1010 floppy disk drive
An Amiga 500 computer system, with 1084S RGB monitor and second A1010 floppy disk drive
TypeHome computer
Release dateApril 1987 (Netherlands), October 1987 (US)
Introductory priceUS$699, £499 (1987)
US$1,600 (2020 equivalent)
Discontinued1991 (1991)
Media880 KiB floppy disks
Operating systemAmigaOS v1.2 – 1.3 (upgradable up to 3.1.4 if 2MB of RAM are installed)
CPUMotorola 68000 @ 7.16 MHz (NTSC)
7.09 MHz (PAL)
Memory512 KiB 150 ns (9 MiB maximum[1])
Graphics736×567i 4-bpp PAL (736×483i 4 bpp NTSC), 368×567i 6 bpp PAL (368×483i 6 bpp NTSC)
Sound4× 8-bit channels PCM at max. 28 kHz with 6-bit volume in stereo
PredecessorAmiga 1000
SuccessorAmiga 500 Plus

The Amiga 500, also known as the A500, is 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. Before it shipped Commodore suggested a list price of US$595.95 without a monitor. At delivery in October 1987 Commodore announced that the machine would carry a US$699/£499 list price.

In Europe the Amiga 500 was released in May 1987.[2] In the Netherlands it was available from April 1987 for a list price of 1499 HFL (US$730 in 1987).[3]

The Amiga 500 represents a return to Commodore's roots by being sold in the same mass retail outlets as the Commodore 64 – to which it was a spiritual successor – as opposed to the computer-store-only Amiga 1000, as well as being another computer whose keyboard is included in the same case.

The original Amiga 500 proved to be Commodore's best-selling Amiga model, enjoying particular success in Europe.[4] Although popular with hobbyists, arguably its most widespread use was as a gaming machine, where its advanced graphics and sound were of significant benefit. It has been claimed that over 6 million A500s were sold worldwide,[citation needed] however, according to Commodore UK, the entire sales of all Amigas in both Europe and the USA were 4-5 million.[citation needed]


In October 1989, the Amiga 500 dropped its price from £499 to £399 and was bundled with the Batman Pack in the United Kingdom (from October 1989 to September 1990) which included the games Batman, F/A-18 Interceptor, The New Zealand Story and the bitmap graphics editor, Deluxe Paint 2.[5] Also included was the Commodore A520 RF Modulator, an adaptor which allowed the A500 to be used with a conventional CRT television set, via its RF antenna socket.

In late 1991, an enhanced model known as the Amiga 500 Plus replaced the original 500 in some markets; it was bundled with the Cartoon Classics pack in the United Kingdom at £399, although many stores still advertised it as an 'A500'.[6]

The Amiga 500 series was discontinued in June 1992[7] and replaced by the similarly specified and priced Amiga 600, although this new machine had originally been intended as a much cheaper model, which would have been the A300. In late 1992, Commodore released the "next-generation" Amiga 1200, a machine closer in concept to the original Amiga 500, 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 popular market was definitively shifting from the home computer platforms of the past to commodity Wintel PCs and the new "low-cost" Macintosh Classic, LC and IIsi models.[8]


Outwardly resembling the Commodore 128[9] and codenamed "Rock Lobster" during development, the Amiga 500 houses the keyboard and CPU in one shell, unlike the Amiga 1000. It utilizes a Motorola 68000 microprocessor running at 7.15909 MHz (NTSC) or 7.09379 MHz (PAL). The CPU implements a 32-bit model, has 32-bit registers and 32-bit internal data bus, but it has a 16-bit main ALU, uses a 16-bit external data bus and 24-bit address bus, providing a maximum of 16 MB of address space.

The earliest Amiga 500 models use nearly the same Original Amiga chipset as the Amiga 1000.[10] So graphics can be displayed in multiple resolutions and color depths, even on the same screen. Resolutions vary from 320×200 (up to 32 colors) to 640×400 (up to 16 colors) for NTSC (704×484 overscan) and 320×256 to 640×512 for PAL (704×576 overscan.)[11] The system uses planar graphics, with up to five bitplanes (four in high resolution) allowing 2-, 4-, 8-, 16-, and 32-color screens, from a palette of 4096 colors. Two special graphics modes are also available: Extra HalfBrite, which uses a 6th bitplane as a mask to cut the brightness of any pixel in half (resulting in 32 arbitrary colors plus 32 more colors set at half the value of the first 32), and Hold And Modify (HAM) which allows all 4096 colors to be used on screen simultaneously.[12] Later revisions of the chipset are PAL/NTSC switchable in software.

The sound chip produces four hardware-mixed channels, two to the left and two to the right, of 8-bit PCM at a sampling frequency of up to 28 kHz. Each hardware channel has its own independent volume level and sampling rate, and can be designated to another channel where it can modulate both volume and frequency using its own output. With DMA disabled it's possible to output with a sampling frequency up to 56 kHz. There's a common trick to output sound with 14-bit precision that can be combined to output 14-bit 56 kHz sound.[13]

The stock system comes with AmigaOS version 1.2 or 1.3 and 512 KiB of chip RAM (150 ns access time), one built-in double-density standard floppy disk drive that is completely programmable and can read 720 KiB IBM PC disks, 880 KiB standard Amiga disks, and up to 984 KiB using custom-formatting drivers.

Despite the lack of Amiga 2000-compatible internal expansion slots, there are many ports and expansion options. There are two DE9M Atari joystick ports for joysticks or mice, stereo audio (RCA connectors 1 V p-p). There is a floppy drive port for daisy-chaining up to three extra floppy disk drives via a DB23F connector.[14] The then-standard RS-232 serial port (DB25M) and Centronics parallel port (DB25F) are also included. The power supply is (+5V, +/-12V).[15] The system displays video in analog RGB 50 Hz PAL or 60 Hz NTSC through a proprietary DB23M connector and in NTSC mode the line frequency is 15,750 Hz HSync for standard video modes, which is compatible with NTSC television and CVBS/RGB video, but out of range for most VGA-compatible monitors, while a multisync monitor is required for some of the higher resolutions. This connection can also be genlocked to an external video signal. The system was bundled with an RF adapter to provide output on televisions with a coaxial RF input, while monochrome composite video is available via an RCA connector (also coaxial). There is also a Zorro bus expansion on the left side (behind a plastic cover). Peripherals such as a hard disk drive can be added via the expansion slot and are configured automatically by the Amiga's AutoConfig standard, so that multiple devices do not conflict with each other. Up to 8 MB of so-called "fast RAM" (memory that can be accessed by the CPU only) can be added using the side expansion slot. This connector is electronically identical with the Amiga 1000's, but swapped on the other side.

The Amiga 500 has a "trap-door" slot on the underside for a RAM upgrade (typically of 512 KiB). This extra RAM is classified as "fast" RAM, but is sometimes referred to as "slow" RAM: due to the design of the expansion bus, it is actually on the chipset bus. Such upgrades usually include a battery-backed real-time clock. All versions of the A500 can have the additional RAM configured as chip RAM by a simple hardware modification, which involves fitting a later model (8372A) Agnus chip. Likewise, all versions of the A500 can be upgraded to 2 MB chip RAM by fitting the 8372B Agnus chip and adding additional memory.

The Amiga 500 also sports an unusual feature for a budget machine, socketed chips, which allow easy replacement of defective chips. The CPU can be directly upgraded on the motherboard to a 68010; or to a 68020, 68030, or 68040 via the side expansion slot; or by removing the CPU and plugging a CPU expansion card into the CPU socket (though this will require opening the computer and voiding any remaining warranty). In fact, all the custom chips can be upgraded to the Amiga Enhanced Chip Set (ECS) versions.

The case is made from ABS plastics which may become brown with time. This may be reversed by using the public-domain chemical mix "Retr0bright", though without a clearcoat to block oxygen, the brown colouring will return.

Whenever the computer is powered on a self-diagnostic test is run that will show any failure with a specific colour where    medium green means no chip RAM found or is damaged,    red means bad kickstart-ROM,    yellow means the CPU has crashed (no trap routine or trying to run bad code) or a bad Zorro expansion card.[16]    Blue means custom chip problem (Denise, Paula, or Agnus),    light green means CIA problem. Stopping on    light gray means that the CIA might be defective.     Black and white stripes mean there is a ROM or CIA problem, while    black only (no video) means there is no video output.[17] The keyboard LED uses blink codes: one blink means the keyboard ROM has a checksum error, two blinks means RAM failure, three blinks means watchdog timer failure.[17] Using Caps Lock key and getting a response means CIA and the CPU works.[17] There is no guarantee that every blinking state or color is accurate. Remember when the diagnostic codes are triggered it means the computer has some kind of fault and it can easily mis-interpret the fault and give false readings. For example, if the screen flashes green it can mean the Agnus is bad, the Agnus socket is bad, the logic connected to the Agnus is bad, the logic connected to the CPU is bad, the logic connected to the RAM is bad, a connection between CPU and/or logic and/or Agnus and/or Chip RAM is bad and/or some/all of the chip RAM is faulty etc. etc. Many of the issues with Amigas are caused by damage from corrosion or poor repair skills, especially the A500+ which has a Ni-Cad battery fitted and is always corroded if the battery has not been removed. Likewise a corroded battery on an A501 can cause faults on the A500 motherboard if the corrosion is very bad and has spread to the motherboard. The self-test chip RAM check is very brief and simplistic and all the other tests are minimalistic to minimize the start-up time (as documented in the Amiga Hardware Manual and many other official Commodore technical documents) so there is no guarantee that any of the diagnostic colours are 100% accurate.[18]

Technical specifications[edit]

The standard Amiga 500 requires floppies to boot
  • OCS (1.2 & 1.3 models) or ECS (1.3 and 500+ 2.04 models) chipset. ECS 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); this allowed 2, 4, 8, 16 and 32 colour screens, from a palette of 4096 colours. Two special graphics modes were 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 SHAM mode, which is based on HAM mode, but used the Copper (part of the Agnus chip which can change hardware registers at given screen positions) to reprogram the color palette registers at each scanline. The advantage of SHM files is 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.[19] The hardware channels have independent volumes (65 levels) and sampling rates, and are 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 (150 ns access time).
  • AmigaOS 1.2 or 1.3 (upgradeable up to 3.1.4[20] if 2MB of RAM are installed)
  • One double-density floppy disk drive is built in, which is completely programmable and thus can read 720 KiB IBM PC disks, 880 KiB standard Amiga disks, and up to 984 KiB with custom formatting (such as Klaus Deppich's diskspare.device). Uses 300 rpm (5 rotations/second) and 250 kbit/s.
  • Built in keyboard.
  • A two-button mouse is included.


  • PAL mode: 320×256, 640×256, 640×512 (interlaced),[21] 704×576 in overscan.
  • NTSC mode: 320×200, 640×200, 640×400 (interlaced),[21] 704×484 in overscan.

Max 6 bpp. The Amiga can show multiple resolution modes at the same time, splitting the screen vertically. An additional mode called Hold-And-Modify (HAM) makes it possible to utilize 12 bpp over a 3 pixels wide span. This works by letting each pixel position use the previous RGB value and modify one of the red, green or blue values to a new 4-bit value. This will cause some negligible colour artifacts however.


Backside with connectors
The Amiga 520 adapter allowed for an RF modulated output, to be connected to a TV


  • 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 larger chips are socketed rather than being TH/SMD soldered directly to the motherboard, so they can be replaced by hand.
  • The CPU can be upgraded to a Motorola 68010 directly or to a 68020, 68030 or 68040 via the side expansion slot or a CPU socket adapter board.
  • 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.
  • The A500+ model instead allowed upgrading by 1 MB trapdoor chip RAM without clock, but there was no visible means on board to map any of this as FAST, causing incompatibility with some stubbornly coded programs.
  • There were modification instructions available for the A500 to solder or socket another 512 RAM on the board, then run extra address lines to the trapdoor slot to accommodate an additional 1 MB of fast or chip RAM depending on the installed chipset.
  • Up to 8 MB of "fast RAM" can be added via the side expansion slot, even more if an accelerator with a non-EC (without reduced data/address bus) processor and 32-bit RAM is used.
  • 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 that extended the bus as they were added – 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.

Memory map[edit]

Address Size in KB Description
0x0000 0000 256.0 Chip RAM
0x0004 0000 256.0 Chip RAM (A1000 option card)
0x0008 0000 512.0 Chip RAM expansion
0x0010 0000 1024.0 Extended Chip RAM for ECS/AGA.
0x0020 0000 8192.0 Primary auto-config space (Fast RAM)
0x00A0 0000 1984.0 Reserved
0x00BF D000 3.8 8520-B (even-byte addresses)
0x00BF E001 3.8 8520-A (odd-byte addresses)
0x00C0 0000 1536.0 Internal expansion memory (pseudo-fast, "slow" RAM on Amiga 500)
0x00D8 0000 256.0 Reserved
0x00DC 0000 64.0 Real time clock
0x00DD 0000 188.0 Reserved
0x00DF F000 4.0 Custom chip registers
0x00E0 0000 512.0 Reserved
0x00E8 0000 64.0 Zorro II auto-config space (before relocation)
0x00E9 0000 448.0 Secondary auto-config space (usually 64K I/O boards)
0x00F0 0000 512.0 512K System ROM (reserved for extended ROM image e.g. CDTV or CD³²)
0x00F8 0000 256.0 256K System ROM (Kickstart 2.04 or higher)
0x00FC 0000 256.0 256K System ROM


Trap-door expansion 501[edit]

An A501 compatible expansion

A popular expansion for the Amiga 500 was the Amiga 501 circuit board that can be installed underneath the computer behind a plastic cover. The expansion contains 512 KiB RAM configured by default as "Slow RAM" or "trap-door RAM" and a battery-backed real-time clock (RTC). The 512 KB trap-door RAM and 512 KB of original chip RAM will result in 1 MB of total memory. By default, the expansion memory is handled and reported by the system as fast memory. However, the RAM is physically connected to Agnus like chip RAM and it is impacted by chip-bus bandwidth contention. Being only accessible by the CPU but as slow as chip RAM, it is commonly being referred to as "Slow RAM". The motherboard can be modified to relocate the trap-door RAM to the chip memory pool, provided a compatible Agnus chip is fitted on the motherboard.

Notable uses[edit]

See also[edit]

Amiga 500 Buyers Guide Amiga 500 buyers guide


  1. ^ Official maximum is 9 MB, various third party extensions exist that increase the 1 MB chip RAM ("slow" RAM) maximum.
  2. ^ "Commodore-Amiga Sales Figures". Archived from the original on 2018-09-27. Retrieved 2020-02-04.
  3. ^ "Nieuwsblad van het Noorden, 1987-04-23".
  4. ^ Gareth Knight. "Commodore-Amiga Sales Figures". Archived from the original on 2009-05-24. Retrieved 2013-07-24.
  5. ^
  6. ^ Gareth Knight (2002-10-21). "Cartoon Classics Bundles". Retrieved 2013-07-24.
  7. ^
  8. ^ Gareth Knight. "Commodore History". Retrieved 2013-07-24.
  9. ^ "Low-End Amiga". BYTE. June 1987. p. 52. Retrieved 5 November 2013.
  10. ^ Agnus was enhanced to control up to 1 MB RAM and glue logic was integrated into Gary to reduce costs.
  11. ^ Peck, Robert; Deyl, Susan; Miner, Jay; Raymond, Chris (September 1986). Amiga hardware reference manual. Addison Wesley. p. 72. ISBN 0-201-11077-6.
  12. ^ Peck, Robert; Deyl, Susan; Miner, Jay; Raymond, Chris (September 1986). Amiga hardware reference manual. Addison Wesley. p. 37. ISBN 0-201-11077-6.
  13. ^ "Aminet: mus/play/Play16.lha". 2003-11-09. Archived from the original on 2020-03-20. Retrieved 2016-02-16.
  14. ^ a b "Hi Res Version, Rear of Amiga 500 - 122K". 070728
  15. ^ a b "Amiga 500/600/1200 Power Connector". Archived from the original on 2007-09-27. Retrieved 2007-08-08. 070808
  16. ^ - Question blinking power LED/no screen on Amiga 500 read 2011-11-03
  17. ^ a b c - A3000 Booting Problems read 2011-11-03
  18. ^ - Discussion relating to incorrect diagnostic of green screen fault on Amiga 500 retrieved 2017-03-02
  19. ^ "Amiga 500". Archived from the original on March 30, 2010. Retrieved December 15, 2009.
  20. ^ "AmigaOS 3.1.4 on A500". Retrieved September 3, 2019.
  21. ^ a b
  22. ^ "Amiga System Memory Map". 090501 Source: Amiga Hardware Reference Manual