Outwardly resembling the
Commodore 128 and codenamed "
Rock Lobster" during development, 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. It uses a Motorola 68000 microprocessor running at in
NTSC regions and in
PAL regions. 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 24-bit address bus, providing a maximum of 16 MB of
address space. Also built in to the base of the computer is a -inch floppy disk drive. The user can also install up to three external floppy drives, either - or -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. The earliest Amiga 500 models use nearly the same
Original Amiga chipset as the Amiga 1000. 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.) 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 sixth 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. 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 . 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 . There is a common trick to
output sound with 14-bit precision that can be combined to output 14-bit sound. The stock system comes with
AmigaOS version 1.2 or 1.3 and of
chip RAM (150 ns access time), one built-in double-density
standard floppy disk drive that is completely programmable and can read
IBM PC disks, standard Amiga disks, and up to 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. The then-standard
RS-232 serial port (DB25M) and
Centronics parallel port (DB25F) are also included. The power supply is (, ). The system displays video in analog
RGB PAL or NTSC through a proprietary DB23M connector and in NTSC mode the line frequency is
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 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 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 ). 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 chip RAM by fitting the 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. == Technical specifications ==