Editing Amiga 500 (section)

== Description ==
Outwardly resembling the [[Commodore 128]]<ref name="byte198706">{{cite news | url=https://archive.org/stream/byte-magazine-1987-06/1987_06_BYTE_12-06_CAD_Mice_12-MHz_ATs_IBM_PS2_Family#page/n55/mode/2up | title=Low-End Amiga | work=BYTE | date=June 1987 | access-date=November 5, 2013 | pages=52}}</ref> and codenamed "[[Rock Lobster]]" during development,<ref>{{cite web |url=http://www.amigahistory.co.uk/b52board.html |title=Mystery Motherboards |author=<!--Not stated--> |date=2002-08-03 |website=amiga history guide |publisher= |archive-url=https://web.archive.org/web/20110208214625/http://www.amigahistory.co.uk/b52board.html |access-date=2022-06-17 |archive-date=February 8, 2011 |quote=Everything George Robbins worked on was some reference to the B-52's.}}</ref> 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 key]]s, 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.{{Sfn|Technical Reference Manual|1987|p=2}} It uses a Motorola 68000 microprocessor running at {{val|7.15909 |ul=MHz}} in [[NTSC]] regions and {{val|7.09379 |u=MHz}} in [[PAL]] regions.{{Sfn|Technical Reference Manual|1987|pp=45–46}} The CPU implements a 32-bit model and has 32-bit registers, but it has a 16-bit main [[Arithmetic logic unit|ALU]] and uses a 16-bit external data bus and a 24-bit address bus, providing a maximum of 16&nbsp;MB of [[address space]].{{efn|name=binpre}}{{Sfn|Greenley|Green|Baker|1991|p=2}}{{Sfn|Technical Reference Manual|1987|p=90}} Also built in to the base of the computer is a {{frac|3|1|2}}-inch floppy disk drive. The user can also install up to three external floppy drives, either {{frac|3|1|2}}- or {{frac|5|1|4}}-inch, via the disk drive port. The second and third additional drives are installed by [[Daisy chain (electrical engineering)|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.{{Sfn|Greenley|Green|Baker|1991|p=6, 335}}

The earliest Amiga 500 models use nearly the same [[Original Amiga chipset]] as the Amiga 1000.{{efn|Agnus was enhanced to control up to {{val|1|ul=MB}}{{efn|name=binpre}} [[random-access memory|RAM]] and glue logic was integrated into [[Amiga custom chips#Gary|Gary]] to reduce costs.}} 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.)<ref name="displaysize">{{cite book|last1 = Peck|first1 = Robert|last2 = Deyl|first2 = Susan|last3 = Miner|first3 = Jay|last4 = Raymond|first4 = Chris|title = Amiga hardware reference manual|publisher = [[Addison Wesley]]|date=September 1986|page = 72|isbn = 0-201-11077-6}}</ref> The system uses [[planar (computer graphics)|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.<ref name=bitplanes>{{harvnb|Peck|Deyl|Miner|Raymond|1986|p=37}}</ref> 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 {{val|28 |ul=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 [[Direct memory access|DMA]] disabled it's possible to output with a sampling frequency up to {{val|56 |u=kHz}}. There is a common trick to [[Original Chip Set#Audio|output sound with 14-bit precision]] that can be combined to output 14-bit {{val|56 |u=kHz}} sound.<ref>{{Cite web |url=http://aminet.net/package/mus/play/Play16 |title=Aminet: mus/play/Play16.lha |date=November 9, 2003 |website=aminet.net |access-date=February 16, 2016 |archive-url=https://web.archive.org/web/20200320173308/http://aminet.net/package/mus/play/Play16 |archive-date=March 20, 2020 |url-status=dead }}</ref>

The stock system comes with [[AmigaOS]] version 1.2 or 1.3 and {{val|512 |u=KB}}{{efn|name=binpre}} of [[Amiga Chip RAM|chip RAM]] (150 ns access time), one built-in double-density [[floppy disk drive|standard floppy disk drive]] that is completely programmable and can read {{val|720 |u=KB}} [[IBM PC]] disks, {{val|880 |u=KB}} standard Amiga disks, and up to {{nowrap|984 KB}} using custom-formatting drivers.

Despite the lack of [[Amiga Zorro II|Amiga 2000-compatible internal expansion slots]], there are many ports and expansion options. There are two [[D-subminiature|DE9M]] [[Atari joystick port]]s for [[joystick]]s or [[mouse (computing)|mice]], and stereo audio [[RCA connector]]s (1&nbsp;V [[peak-to-peak|p-p]]). There is a floppy drive port for daisy-chaining up to three extra floppy disk drives via a DB23F connector.<ref name="gbwxgm">{{cite web|website=amigahardware.mariomisic.de|title=Hi Res Version, Rear of Amiga 500 – 122K|url=http://amigahardware.mariomisic.de/download_photos/a500_4_big.jpg|access-date=July 27, 2007|archive-date=August 9, 2007|archive-url=https://web.archive.org/web/20070809235410/http://amigahardware.mariomisic.de/download_photos/a500_4_big.jpg|url-status=live}} 070728 amigahardware.mariomisic.de</ref> The then-standard [[RS-232]] serial port (DB25M) and [[Centronics]] [[parallel port]] (DB25F) are also included. The power supply is ({{val|+5|u=V}}, {{val|p=±|12|u=V}}).<ref name=itgehi>{{cite web|website=www.ntrautanen.fi|title=Amiga 500/600/1200 Power Connector|url=http://www.ntrautanen.fi/computers/hardware/misc/a500_power.htm|access-date=August 8, 2007|archive-url=https://web.archive.org/web/20070927010556/http://www.ntrautanen.fi/computers/hardware/misc/a500_power.htm|archive-date=September 27, 2007|url-status=dead}} 070808 ntrautanen.fi</ref> 
The system displays video in analog [[component video|RGB]] {{val|50 |ul=Hz}} PAL or {{val|60 |u=Hz}} NTSC through a proprietary DB23M connector and in NTSC mode the line frequency is {{val|15.75 |u=kHz}} [[synchronization|HSync]] for standard video modes, which is compatible with NTSC television and CVBS/RGB video, but out of range for most [[video graphics array|VGA]]-compatible monitors, while a [[multisync monitor]] is required for some of the higher resolutions. This connection can also be [[genlock]]ed to an external video signal. The system was bundled with an [[RF modulator|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 {{val|8 |u=MB}}{{efn|name=binpre}} 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 {{val|512 |u=KB}}){{efn|name=binpre}}. 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) [[MOS Technology Agnus|Agnus]] chip. Likewise, all versions of the A500 can be upgraded to {{val|2 |u=MB}}{{efn|name=binpre}} chip RAM by fitting the {{nowrap|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 [[Motorola 68010|68010]]; or to a [[Motorola 68020|68020]], [[Motorola 68030|68030]], or [[Motorola 68040|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 [[Stabilizer (chemistry)|stabilizing agents]] or antioxidants to block oxygen, the yellowing will return.<ref>{{cite web|url=https://www.theguardian.com/technology/blog/2009/mar/04/gadgets|title=What does it take to clean my old computer?|last=Johnson|first=Bobbie|work=[[The Guardian]]|date=March 4, 2009|access-date=November 24, 2021|archive-url=https://web.archive.org/web/20211124094207/https://www.theguardian.com/technology/blog/2009/mar/04/gadgets|archive-date=November 24, 2021|url-status=live}}</ref><ref>{{cite book|title=Plastics Additives: An A-Z reference|last=Pritchard|first=Geoffrey|series=Polymer Science and Technology Series |publisher=[[Springer Science+Business Media]]|date=1998|volume=1 |pages=55–56, 472–473|doi=10.1007/978-94-011-5862-6|isbn=978-94-011-5862-6}}</ref>