Editing Amstrad CPC (section)

==Hardware==

===Processor===
The entire CPC series is based on the [[Zilog Z80]]; a processor, clocked at 4&nbsp;[[Hertz|MHz]].<ref name="464 Tech spec">Technical Specification, CPC464 Service Manual, p. 2., Amstrad Consumer Electronics Plc.</ref> In order to avoid the CPU and the video logic simultaneously accessing the shared main memory and causing video corruption ("snowing"), CPU memory access is constrained to occur on [[microsecond]] boundaries. This effectively pads every machine cycle to four [[clock cycle]]s, causing a minor loss of processing power and resulting in what Amstrad estimated to be an "effective clock rate" of "approximately 3.3&nbsp;MHz".<ref name="SOFT968">CPC464/664/6128 Firmware (Soft 968), Section 1</ref>

===Memory===
Amstrad CPCs are equipped with either 64 (CPC 464, CPC 664, 464plus, GX4000) or 128 (CPC 6128, 6128plus)&nbsp;KB of RAM.<ref name="464 Tech spec"/><ref name="6128 Tech spec">Technical Specification, CPC6128 Service Manual, p. 31., Amstrad Consumer Electronics Plc.</ref> This base memory can be extended by up to 512&nbsp;KB using memory expansions sold by third-party manufacturers, and by up to 4096&nbsp;KB using experimental methods developed by hardware enthusiasts. Because the Z80 processor is only able to directly address 64&nbsp;KB of memory, additional memory from the 128&nbsp;KB models and memory expansions is made available using [[bank switching]].

===Video===
[[File:Schneider CPC6128 with green monitor GT65, Wikipedia logo.jpg|thumb|Mode 1 image on a GT65 green monitor]]
Underlying a CPC's video output is the unusual pairing of a [[Cathode Ray Tube Controller|CRTC]] ([[Motorola 6845]] or compatible) with a custom-designed [[gate array]] to generate a pixel display output. CPC 6128s later in production as well as the models from the plus range integrate both the CRTC and the gate array's functions with the system's [[Application-specific integrated circuit|ASIC]].

Three built-in display resolutions are available: 160×200 pixels with 16 colours ("Mode 0", 20 text columns), 320×200 pixels with 4 colours ("Mode 1", 40 text columns), and 640×200 pixels with 2 colours ("Mode 2", 80 text columns).<ref name="464 Tech spec"/> Increased screen size can be achieved by reprogramming the CRTC.

The original CPC video hardware supports a [[Palette (computing)|colour palette]] of 27 colours,<ref name="464 Tech spec"/> generated from [[RGB]] colour space with each colour component assigned as either off, half on, or on ([[List of monochrome and RGB color formats#3-level RGB|3 level RGB palette]]). The plus range extended the palette to 4096 colours, also generated from RGB with 4 bits each for red, green and blue ([[List of monochrome and RGB color formats#12-bit RGB|12-bit RGB]]).<ref name="ArnoldVSpec"/>

[[File:Amstrad MP-1.jpg|thumb|Amstrad MP1 external television adapter]]
With the exception of the GX4000, all CPC models lack an [[RF modulator|RF television]] or [[composite video]] output and instead shipped with a 6-pin RGB [[DIN connector]], also used by Acorn computers, to connect the supplied Amstrad monitor.<ref name="464 Tech spec"/> This connector delivers a 1v p-p analogue RGB with a 50&nbsp;Hz composite sync signal that, if wired correctly, can drive a 50&nbsp;Hz [[SCART]] television. External adapters for RF television were available as a first-party hardware accessory.

===Audio===
The CPC uses the [[General Instrument AY-3-8910|General Instrument AY-3-8912]] [[sound chip]],<ref name="464 Tech spec"/> providing three channels, each configurable to generate square waves, white noise or both. A small array of hardware volume envelopes are available.

Output is provided in mono by a small (4&nbsp;cm) built-in loudspeaker with volume control, driven by an internal [[amplifier]]. [[Stereophonic sound|Stereo]] output is provided through a {{nowrap|3.5 mm}} [[headphones]] jack.

It is possible to play back [[sampling (signal processing)|digital sound samples]] at a resolution of approximately 5-bit by sending a stream of values to the sound chip. This technique is very processor-intensive and hard to combine with any other processing. Examples are the title screens or other non-playable scenes of games like ''[[Chase H.Q.]]'', ''[[Meltdown (8-bit video game)|Meltdown]]'', and ''[[RoboCop (1988 video game)|RoboCop]]''.  The later Plus models incorporated a DMA engine in order to offload this processing.

===Floppy disk drive===
[[File:Schneider CPC6128 Diskettenlaufwerk.jpg|thumb|Built-in disk drive of the CPC 6128]]
[[File:CPC6128 loading Turbo Esprit from floppy disk.flac|thumb|A CPC 6128 loading ''[[Turbo Esprit]]'' from its internal floppy drive]]
[[File:3 inch floppy disks.jpg|right|thumbnail|3-inch floppy disks used on CPC machines]]
Amstrad uses [[Panasonic|Matsushita's]] 3" floppy disk drive [ref: CPCWiki], which was compatible with [[Hitachi]]'s existing [[Compact Floppy|3" floppy disk format]].<ref name="pountain198501" /> The chosen drive (built-in for later models) is a single-sided 40-track unit that requires the user to remove and flip the disk to access the other side.<ref name="6128 Tech spec"/> Each side has its own independent write-protect switch.<ref name="6128 Tech spec"/> The sides are termed "A" and "B", with each one commonly formatted to 180&nbsp;KB (in [[AMSDOS]] format, comprising 2&nbsp;KB directory and 178&nbsp;KB storage) for a total of 360&nbsp;KB per disk.

The interface with the drives is an NEC 765 [[Floppy disk controller|FDC]], used for the same purpose in the IBM [[IBM Personal Computer XT|PC/XT]], [[PC/AT]] and [[IBM Personal System/2|PS/2]] machines. Its features are not fully used in order to cut costs, namely [[Direct memory access|DMA]] transfers and support for [[single density]] disks; they were formatted as [[double density]] using [[modified frequency modulation]].

Discs were shipped in a paper sleeve or a hard plastic case resembling a [[compact disc]] "jewel" case. The casing is thicker and more rigid than that of 3.5&nbsp;inch diskettes, and designed to be mailed without any additional packaging{{Citation needed|date=December 2010}}. A sliding metal cover to protect the media surface is internal to the casing and latched, unlike the simple external sliding cover of Sony's version. They were significantly more expensive than both 5.25&nbsp;inch and 3.5&nbsp;inch alternatives. This, combined with their low nominal capacities and their essentially proprietary nature, led to the format being discontinued shortly after the CPC itself was discontinued.

Apart from Amstrad's other 3-inch machines (the [[Amstrad PCW|PCW]] and the [[ZX Spectrum|ZX Spectrum +3]]), the few other computer systems to use them included the [[Sega]] SF-7000 and CP/M systems such as the [[Tatung Einstein]] and [[Osborne Computer Corporation|Osborne]] machines. They also found use on embedded systems.

The [[Shugart bus|Shugart]]-standard interface means that Amstrad CPC machines are able to use standard 3", 3½" or 5¼" drives as their second drive. Programs such as ROMDOS and ParaDOS extend the standard AMSDOS system to provide support for double-sided, 80-track formats, enabling up to 800&nbsp;KB to be stored on a single disk.

The 3-inch disks themselves are usually known as "discs" on the CPC, following the spelling on the machine's plastic casing and conventional [[British English spelling]].

===Expansion===
[[File:Amstrad CPC646-IMG 7196.jpg|thumb|Back of the case of a CPC 464, with the mini-jack, joystick and printer ports.]]
The hardware and firmware was designed to be able to access software provided on external ROMs. Each ROM has to be a 16&nbsp;KB block and is switched in and out of the memory space shared with the video RAM. The Amstrad firmware is deliberately designed so that new software could be easily accessed from these ROMs. Popular applications were marketed on ROM, particularly word processing and programming utility software (examples are Protext and Brunword of the former, and the MAXAM assembler of the latter type).

Such extra ROM chips do not plug directly into the CPC itself, but into extra plug-in "rom boxes" which contain sockets for the ROM chips and a minimal amount of decoding circuitry for the main machine to be able to switch between them. These boxes were either marketed commercially or could be built by competent hobbyists and they attached to the main expansion port at the back of the machine. Software on ROM loads much faster than from disc or tape and the machine's boot-up sequence was designed to evaluate ROMs it found and optionally hand over control of the machine to them. This allows significant customisation of the functionality of the machine, something that enthusiasts exploited for various purposes.<ref name="Amstrad CPC ROM expansion">{{Cite web|url=http://8bit.yarek.pl/hardware/cpc.rom/index.html|title=ROM :: Amstrad CPC -- 8bit Projects For Everyone|website=8bit.yarek.pl|access-date=1 November 2009|archive-date=8 August 2009|archive-url=https://web.archive.org/web/20090808173010/http://8bit.yarek.pl/hardware/cpc.rom/index.html|url-status=dead}}</ref> However, the typical users would probably not be aware of this added ROM functionality unless they read the CPC press, as it is not described in the user manual and was hardly ever mentioned in marketing literature. It is, however, documented in the official Amstrad firmware manual.

The machines also feature a 9-pin [[Atari joystick port]] that will either directly take one joystick, or two joysticks by use of a splitter cable.<ref name="464 Tech spec"/>