Amiga 500

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 Amiga video connector which allows the A500 to be used with a conventional CRT television.

In November 1991, the enhanced Amiga 500 Plus replaced the 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 Plus was virtually identical except for its new operating system, and in mid-1992, the two were discontinued and effectively replaced by the Amiga 600.[7] In late 1992, Commodore released the Amiga 1200, a machine closer in concept to the original Amiga 500, but with significant technical improvements. Despite this, neither the A1200 nor the A600 replicated the commercial success of its predecessor. By this time, the home market was strongly shifting to IBM PC compatibles with VGA graphics and the "low-cost" Macintosh Classic, LC, and IIsi models.[8]

Outwardly resembling the Commodore 128[9] and codenamed "Rock Lobster" during development,[10] the Amiga 500's base houses a keyboard and a CPU in one shell, unlike the Amiga 1000. The keyboard for Amiga 500s sold in the United States contains 94 keys, including ten function keys, four cursor keys, and a number pad. All European versions the keyboard have an additional two keys, except for the British variety, which still uses 94 keys.[11] It uses a Motorola 68000 microprocessor running at 7.15909 MHz in NTSC regions and 7.09379 MHz in PAL regions.[12] The CPU implements a 32-bit model and has 32-bit registers, but it has a 16-bit main ALU and uses a 16-bit external data bus and a 23-bit address bus, providing a maximum of 16 MB of address space.[2][13][14] Also built in to the base of the computer is a 3+1⁄2-inch floppy disk drive. The user can also install up to three external floppy drives, either 3+1⁄2- or 5+1⁄4-inch, via the disk drive port. The second and third additional drives are installed by daisy-chaining them. Supported by these drives are double-sided disks with a capacity of 901,120 bytes, as well as 360- and 720-KB disks formatted for IBM PC compatibles.[15]

The earliest Amiga 500 models use nearly the same Original Amiga chipset as the Amiga 1000.[lower-alpha 2] 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.)[16] 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.[17] 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 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 is a common trick to output sound with 14-bit precision that can be combined to output 14-bit 56 kHz sound.[18]

The stock system comes with AmigaOS version 1.2 or 1.3 and 512 KB[2] of chip RAM (150 ns access time), one built-in double-density standard floppy disk drive that is completely programmable and can read 720 KB IBM PC disks, 880 KB standard Amiga disks, and up to 984 KB 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, and 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.[19] The then-standard RS-232 serial port (DB25M) and Centronics parallel port (DB25F) are also included. The power supply is (+5V, +/-12V).[20] 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 15.75 kHz 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). On the left side, behind a plastic cover, there is a Zorro (Zorro I) bus expansion external edge connector with 86 pins. 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[2] 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 512 KB)[2]. 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[2] 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 (this requires opening the computer and thus voided any remaining warranty). In fact, all the custom chips can be upgraded to the Amiga Enhanced Chip Set (ECS) versions.

The plastic case is made of acrylonitrile butadiene styrene, or ABS. ABS degrades with time due to exposure to oxygen, causing a yellowing of the case. Other factors contributing to the degradation and yellowing include heat, shear, and ultraviolet light. The yellowing can be reversed by using an optical brightener, though without stabilizing agents or antioxidants to block oxygen, the yellowing will return.[21][22]

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.
  • Sound: 4 hardware-mixed channels of 8-bit sound at up to 28 kHz.[23] 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[2] of chip RAM (150 ns access time).
• AmigaOS 1.2 or 1.3 (upgradeable up to 3.1.4[24] if 2 MB[2] of RAM are installed)
• One 3.5" double-density floppy disk drive is built in, 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). Uses 300 rpm (5 rotations/second) and 250 kbit/s.
• Built-in keyboard.
• A two-button mouse is included.

Connectors

Backside of the base of the Amiga 500. From left to right, it features two Atari joystick ports, two audio connectors, a floppy drive port, a serial and a parallel port, a power input, and two separate inputs for RGB and monochrome monitors.[27]

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

• Two Atari joystick ports for joysticks or mice
• Stereo audio RCA connectors (1 V p-p)
• A floppy drive port (DB23F), for daisy-chaining up to 3 extra floppy disk drives via a DB23F connector[19]
• A standard RS-232 serial port (DB25M)
• A parallel port (DB25F)
• Power inlet (+5 V, +/-12 V)[20]
• 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 frequently bundled with the machine to provide output on regular televisions or on composite monitors. 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 on the left side behind a plastic cover
• Trapdoor slot under the machine, for RAM expansion and real-time clock

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 KB 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.[2] The added memory is known as "Slow RAM", as its access is impacted by chip-bus bandwidth contention, while the chipset is not actually able to address it.

Later revisions of the motherboard provide solder-jumpers to relocate the trap-door RAM to the chip memory pool, given the Agnus chip is the newer ECS version, shipped in later A500 motherboards. Newest (rev 8) A500s would share motherboard with A500+, and configure the expansion memory as CHIP by default.

Each time the Amiga 500 is booted, it executes code from the Kickstart ROM. The Amiga 500 initially came shipped with AmigaOS 1.2, but units since October 1988 had version 1.3 installed.[30][31]

The Amiga 500 was the best-selling model in the Amiga family of computers. The German computer magazine Chip awarded the model the annual "Home Computer of the Year" title three consecutive times.[32] At the European Computer Trade Show 1991, it also won the Leisure Award for the similar "Home Computer of the Year" title.[33] Owing to the inexpensive cost of the Amiga 500 in then price-sensitive Europe, sales of the Amiga family of computers were strongest there, constituting 85 percent of Commodore's total sales in the fourth quarter of 1990. The Amiga 500 was widely perceived as a gaming machine and the Amiga 2000 a computer for artists and hobbyists.[34] It has been claimed[35][36][37] that Commodore sold as many as six million units worldwide. However, Commodore UK refuted that figure and said that the entire Amiga line sold between four and five million computers.[1] Indeed, Ars Technica provides a year-by-year graph of the sales of all Amiga computers.[38]

Commodore Amiga 500 Plus

Base of the Amiga 500 Plus, with the Italian variant of the keyboard
Developer	Commodore International
Product family	Amiga
Type	Home computer
Release date	1991 (1991) (UK)
Discontinued	1992
Media	880 KB floppy disks
Operating system	AmigaOS v2.04
CPU	Motorola 68000 @ 7.16 MHz (NTSC) 7.09 MHz (PAL)
Memory	1 MB (10 MB maximum)
Display	640×256, 4 bpp @ 50 Hz (PAL) 640×200, 4 bpp @ 60 Hz (NTSC)
Sound	4× 8-bit channels PCM at max. 28 kHz with 6-bit volume in stereo
Predecessor	Amiga 500
Successor	Amiga 600

The Amiga 500 Plus (often A500 Plus or simply A500+) is a revised version of the original Amiga 500 computer. The A500+ featured minor changes to the motherboard to make it cheaper to produce than the original A500. It was notable for introducing new versions of Kickstart and Workbench, and for some minor improvements in the custom chips, known as the Enhanced Chip Set (or ECS).

Although officially introduced in 1992, some Amiga 500 units sold in late 1991 actually featured the revised motherboard used in the A500+. Although the Amiga 500+ was an improvement to the Amiga 500, it was minor. It was discontinued and replaced by the Amiga 600 in summer 1992, making it the shortest-lived Amiga model.

• Amiga models and variants
• Minimig – an open-source hardware FPGA implementation

• Introduction To The Amiga 500. Commodore International. 1987. Retrieved November 24, 2021.
• Greenley, Larry; Green, Mark; Baker, Dan (August 1991). Amiga Hardware Reference Manual (Third ed.). Addison-Wesley. ISBN 0-201-56776-8. Retrieved November 24, 2021.
• Commodore Amiga A500/A2000 Technical Reference Manual. Commodore International. 1987. Retrieved November 25, 2021.
• Commodore International (June 1990). Amiga ROM Kernal Reference Manual: Libraries And Devices (2nd ed.). Addison-Wesley. ISBN 0-201-18187-8. Retrieved November 25, 2021.
• Maher, Jimmy (2018). The Future Was Here: The Commodore Amiga. MIT Press. doi:10.7551/mitpress/9022.001.0001. ISBN 9780262535694. Retrieved November 19, 2021.

Wikimedia Commons has media related to Amiga 500.

• Amiga 500 Buyers guide