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Amstrad CPC
Type	Personal computer
Released	1984
Discontinued	1990
Processor	Zilog Z80A @ 4 MHz
Memory	64 to 576 KB (KiB)
Operating system	Locomotive BASIC 1.0, 1.1 and CP/M

The Amstrad CPC was a series of 8-bit home computers produced by Amstrad during the 1980s and early 1990s. CPC stood for 'Colour Personal Computer', although it was possible to purchase a CPC with a green screen (GT65/66) as well as with the standard colour screen (CTM640).

The first machine, the CPC 464 was introduced in 1984. It was designed to be a direct competitor to the Commodore 64 and Sinclair ZX Spectrum systems. The CPC range was very successful, and over 3 million were sold during the machine's lifespan.^[1]

Outwardly, the most distinguishing features of Amstrad's offering were the matt black console case with sharp corners and narrowly rectangular form factor (the latter due to the built-in cassette tape deck (CPC 464) or floppy disk drive (CPC 664 and CPC 6128), the keyboard's distinctly coloured special keys (all the non-typewriter-standard keys on the 464 and 664), and the unique power supply hookup with one lead going from the monitor to the computer (or RF modulator) and, on disc-based machines, one lead going the other way. A television could be used with an optional adapter, and an optional tuner was available to turn the monitor into a TV.

Contents 1 The Amstrad CPC sold as a "complete system" 2 The CPC family 2.1 The Amstrad CPC 464, 472, 664, 6128 2.2 West Germany: Schneider CPC 464, 664 and 6128 2.3 East Germany: KC compact 2.4 The CPC 5512 2.5 Plus models 3 Hardware description 3.1 Video (graphics): modes, outputs 3.2 Audio (sound) 3.3 The 3" floppy disk drives 3.4 Serial port adaptor 4 Software 4.1 Built-in BASIC and operating system 4.2 Other languages 4.3 Notable games, with screenshots 4.4 The Roland series 5 Magazines 6 The Amstrad CPC vs. its competitors 6.1 Amstrad vs C64 6.2 Amstrad vs Spectrum 6.3 Amstrad vs BBC Micro 7 Influence on other Amstrad machines 8 Hardware tricks on the CPC series 8.1 CRTC programming tricks 8.2 Sound tricks 9 Emulators 9.1 Software-based 9.2 Hardware-based 10 See also 11 Notes and references 12 External links

Amstrad initially promoted the CPC as being an improvement on the competing ZX Spectrum and C64 because it was a complete system - including everything required to use the machine in one box. Compared to a C64 or a ZX Spectrum, the Amstrad CPCs shipped with their own monitor, had a built in tape recorder or floppy disk drive and even a small loudspeaker. This marketing gave a more "professional" appeal to the Amstrad CPC by marketing it in the same way as business-oriented systems, rather than gaming or home oriented ones.

As a late entrant to the European 8-bit market, the CPC range never achieved the total sales volume of either the ZX Spectrum or the C64, but the advantages of a proper typewriter-style keyboard and integrated tape or floppy drive saw it obtain considerable market share in the late 80s. It became the best-selling computer in France at this time, and was also popular in Spain. Many of the best software titles for the CPC were created on the continent, but only a limited number saw commercial release in the UK.

The Firmware and Software were produced by Locomotive Software and the hardware design was carried out by MEJ Electronics, otherwise known as Mark-Eric Jones.

The original CPC was sold in the following configurations:

• CPC 464 – Tape deck, 64 KB RAM, square-edged keyboard
• CPC 472 – Tape deck, 72 KB RAM (although the extra 8 KB of RAM could not be used because the chip was not connected, only soldered to a dummy PCB); produced in small numbers for the Spanish market to avoid a legal ruling requiring that all computers with 64 KB or less RAM must be localized to the Spanish language, including the keyboard and screen messages. The law was subsequently changed to include machines with more than 64 KB RAM so a localised version of the 472 also exists [2].
• CPC 664 – 3" Floppy disk drive, 64 KB RAM, bowed keyboard; short-lived model, quickly replaced by the better-specified 6128
• CPC 6128 – 3" Floppy disk drive, 128 KB RAM (accessed using bank switching), more PC-like keyboard

An external disk drive (DDI-1) was available for the 464, incorporating the DOS in an interface unit. A second drive (FD-1) could be added to both this and 664/6128 machines. Cassette recorders could also be connected to the 664 and 6128. By and large, the later versions were compatible with earlier machines, though there were some incompatibilities in undocumented features. Third-party hardware add-ons such as Romantic Robot's popular Multiface allowed DIY backup of most tape software to disk.

Most games, especially in the early years, targeted the 64 KB RAM 464 and 664 models. However, an increasing number of applications and demos made use of the extra memory of the 6128 as time went on, to the extent that much CPC software from the 1990s will not run on an unexpanded 464/664. RAM expansions were available, the most popular being produced by dk'Tronics.

The memory layout of the system allowed the CPCs to run CP/M 2.2 and CP/M software adapted especially for the machines' terminal emulation was not uncommon. An Amstrad-specific variant of CP/M 3.1 (aka CP/M Plus) was shipped with the 6128.

Amstrad's German partner company Schneider produced its own models of the CPC 464, 664 and 6128. These machines had grey keys in place of the Amstrad coloured alternatives, and industry-standard D-connector Centronics ports in place of the edge connectors. They were otherwise identical at the hardware level, with a link on the PCB being set to configure the sign-on message as Schneider rather than Amstrad. Documentation and case labels were translated into German.

Like most other computers of the era, the CPC inspired a clone in the Eastern bloc - the KC compact, made in East Germany using Soviet and East German components.

The machine differed from a CPC visually with a different style of case, external power supply and (optional and even more scarce than the main device) external 5.25" Robotron disc drive. Unlike the Amstrad models it could be used with a television screen out of the box. It ran BASIC 1.1 and a CP/M clone, the German-language MicroDOS. It had 64 KB RAM built in and an additional 64 KB RAM was provided with the external disc/tape drive adapter.

The Z80 processor was replaced with a U 880 (which is 100% bug-compatible), and some proprietary Amstrad I/O chips replaced with clones based on the Z8536. This clone machine was around 95% compatible with the original.

The "CPC 5512" was an April Fool concocted by weekly French computer magazine, Hebdogiciel. The purported specifications included 512 KB RAM, a 5.25" floppy disk drive, and Digital Research's GEM on a CPC 6128 clone. Amstrad France eventually decided not to sue for lost trade, but forced the magazine to offer a refund of the purchase price to any disappointed readers.

In 1990 Amstrad introduced the "Plus" series which tweaked the hardware in many ways and added a cartridge slot to all models. Most improvements were to the video display which saw an increase in palette to 4096 colours and gained a capacity for hardware sprites. Splitting the display into separate modes and pixel scrolling both became full supported hardware features, although the former was easy, and the latter possible to some degree, on the non-"Plus" hardware using clever programming of the existing Motorola 6845.

An automatic DMA transfer system for feeding the sound chip was also added, enabling high-quality samples to be replayed with minimal processor overhead; the sound chip itself, however, remained unchanged. Additionally, the BASIC command set for disc access was improved.

A cut down CPC+ without the keyboard nor support for non-cartridge media was released simultaneously as the GX4000 video game console.

These models did not do very well in the marketplace, failing to attract any substantial third party support. The 8-bit technology behind the CPC was starting to look out-of-date by 1990, and Amstrad's marketing failed to promote any significant advantage over the competing Atari ST and Commodore Amiga systems. There is some anecdotal suggestion that users resented the substantial price hike for cartridge games compared to their tape and disc counterparts, likely exacerbated by the tendency to rerelease old CPC games on cartridge without taking advantage of the enhanced Plus hardware.

All CPC models were based on a Zilog Z80 processor clocked at 4 MHz. Because a common pool of RAM is shared with the video circuits, the Z80 may only make a memory accesses every four cycles - which has the effect of rounding all instruction cycle lengths up to the next multiple of four. The speed is therefore roughly equivalent to a 3.3 MHz machine.

The system came with 64 KB or 128 KB of RAM depending on the model (capable of being expanded to 512k within the Amstrad-standard address space). The machines also featured an (almost) standard 9-pin Atari-style joystick socket which was able to take two joysticks via a splitter.

Underlying the CPC's video output was the Motorola 6845 address generator. This chip was connected to a pixel generator that supported 4 bpp, 2 bpp and 1 bpp output (bpp = bits per pixel). The address generator was clocked at a constant rate so the 4 bpp display generated half as many pixels as the 2 bpp and a quarter as many as the 1 bpp. Three built-in display resolutions were available, though increased screen size could be achieved by reprogramming the 6845.

The standard video modes were:

• Mode 0: 160×200 pixels with 16 colors (4 bpp)
• Mode 1: 320×200 pixels with 4 colors (2 bpp)
• Mode 2: 640×200 pixels with 2 colors (1 bpp)

A colour palette of 27 colors was supported, derived from RGB colour space with each component assigned as either off, half on or on. The later Plus models extended this to 4096 colours and added support for hardware sprites.

This hardware compares well with the other 8-bit computers. In particular the CPC lacks the colour clash of the ZX Spectrum and clever programming of the 6845 could produce overscan, different resolutions (although with the same pixel density), and smooth pixel scrolling.

The machine lacked either an RF TV or composite video output and instead shipped with a proprietary 6-pin DIN connector intended for use solely with the supplied Amstrad monitor. An external adapter for RF TV was available to be bought separately.

The 6-pin DIN connector is capable of driving a SCART television with a correctly wired lead. The video signals are PAL frequency 1v p-p analogue RGB with composite sync.

The CPC used the General Instrument AY-3-8912 sound chip, providing three channels, each configurable to generate square waves, white noise or both. A small array of hardware volume envelopes are available.

Output was provided in mono by a small (4 cm) built-in loudspeaker with volume control, driven by an internal amplifier. Stereo output was provided through a 3.5 mm headphones jack.

Playback of digital sound samples at a resolution of approximately 5-bit, as heard on the title screen of the game RoboCop, was possible by sending a stream of values to the sound chip. This trick was very processor-intensive and hard to combine with any other processing.

Amstrad's idiosyncratic choice of Hitachi's 3" floppy disk drive, when the rest of the PC industry was moving to Sony's 3.5" format, is often claimed to be due to Amstrad bulk-buying a large consignment of 3" drive units in Asia. The chosen drive (built-in in later models) was a single-sided 40-track unit that required the user to physically remove and flip the disk to access both sides. Each side had its own independent write-protect switch. The sides were termed "A" and "B", with each one commonly formatted to 180 kB (in AMSDOS format, comprising 2 kB directory and 178 kB storage) for a total of 360 kB per disc.

The interface with the drives was a NEC 765 FDC, used for the same purpose in the IBM PC/XT, PC/AT and PS/2 machines. Many of its features were unused in order to cut costs, namely DMA transfers and support for single density disks; they were formatted as double density using Modified frequency modulation.

Disks were typically 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" diskettes. 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 (some reviews at the time reported driving over them with no problems). Because of this they were significantly more expensive than both 5.25" and 3.5" 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" machines (the PCW and the ZX Spectrum +3), the few other computer systems to use them included the Sega SF-7000 and mostly obscure and exotic CP/M systems such as the Tatung Einstein and Osborne machines. They also found some use on embedded systems.

The Shugart-standard interface meant that Amstrad CPC machines were able to use standard 3", 3½" or 5¼" drives as their second drive. Programs such as ROMDOS and ParaDOS extended the standard AMSDOS system to provide support for double-sided, 80-track formats, enabling up to 800k to be stored on a single disk.

Amstrad issued two RS-232-C D25 serial interfaces, attached to the expansion connector at the rear of the machine, with a through-connector for the CPC464 disk drive or other peripherals. The original interface came with a "Book of Spells" for facilitating data transfer between other systems using a proprietary protocol in the device's own ROM, as well as terminal software to connect to British Telecom's Prestel service. A separate version of the ROM was created for the U.S. market due to the use of the commands "SUCK" and "BLOW", which were considered unacceptable there.

Software and hardware limitations in this interface led to its replacement with an Amstrad-branded version of a compatible alternative by Pace. Other serial interfaces were available from third-party vendors such as KDS Electronics and Cirkit.

Like most home computers at the time, the CPC had its OS and a BASIC interpreter built in as ROM. It used Locomotive BASIC - an improved version of Locomotive Software's Z80 BASIC for the BBC Microcomputer co-processor board. This was faster, more comfortable and more powerful than the generic but common Microsoft BASIC used by the Commodore 64 and MSX amongst others. It was particularly notable for providing easy access to the machine's video and audio resources in contrast to the arcane POKE commands required on generic Microsoft implementations.

Although it was possible to obtain compilers for Locomotive BASIC, C and Pascal, the majority of the CPC's software was written in native Z80a assembly language. Popular assemblers were Hisoft's Devpac, Arnor's Maxam, and (in France) DAMS. All disk-based CPC (not Plus) systems shipped with an interpreter for the educational language LOGO, booted from CP/M 2.2 but largely CPC-specific with much code resident in the AMSDOS ROM.

Cybernoid 2	Turrican	Switchblade
Crafton&Xunk (Get Dexter)

At launch, Amsoft had lined up a range of 50 games. Apparently at the behest of Alan Sugar himself, a number of these (as well as several subsequent releases) were tagged with the Roland name, in an attempt to give the CPC a recognisable mascot. However, since many of the games had not been designed around the Roland character and only had the branding added later there was initially no consensus on what kind of games Roland should star in or even what he looked like. Roland's appearance varied immensely, from a spiky-haired blonde teenager (Roland Goes Digging) to a mutant flea (Roland In The Caves) to a white cube with legs (Roland Goes Square Bashing) to something resembling Luigi from the Mario games (Roland On The Ropes). Eventually it was decided that Roland should be a squat man in a blue hat, red jumper and yellow trousers. The character was named after Roland Perry, a technical manager at Amstrad.

The games in the series were:

• Roland In The Caves (Indescomp, 1984) (This was the game which inspired Alan Sugar to conceive the Roland series)
• Roland Ahoy (Computersmith, 1984)
• Roland On The Ropes (Indescomp, 1984) (This was a pack in with the original CPC bundle)
• Roland Goes Digging (Gem, 1984)
• Roland On The Run (Epicsoft, 1984)
• Roland Goes Square Bashing (Durell, 1984)
• Roland In Time (Gem, 1984)
• Roland In Space (Gem, 1985)

Magazines available for the system (at various times) included Amtix!, Computing With The Amstrad, Amstrad Computer User (Amstrad official publication), Amstrad Action, Amstradbladet, and CPC Attack.

Since the Amstrad CPC was specifically built to compete with the ZX Spectrum and C64, and was a relatively late entrant into the 1980s 8-bit home computer market, comparisons between those computer systems were frequent in specialist magazines but also among users themselves. Because many games were released simultaneously for the three machines, it was easy - and tempting - to compare quality, technical characteristics, and platform-dependent peculiarities.

The C64 had better sound and scrolling capabilities than its competitors thanks to its dedicated hardware. In particular, its sound-generation facilities were superior, due to the SID chip.

However, C64 floppy drives were notoriously slow, due to bad OS coding on Commodore's behalf^{[citation needed]} (although this was solved via turbo software or turbo cartidges allowing for example most of the disk operations to run 10 times faster).^{[citation needed]} The C64 also suffered from a relatively primitive built-in BASIC dialect (this could be solved via software by BASIC language extender programs loaded from disk, tape or included in plug-in cartridges). Although an objective viewpoint might see the C64 as the most successful 8-bit machine, the CPC arguably managed a more respectable showing for non-games software.

The Spectrum had the simplest hardware of the three. As a result, it suffered from colour clash and the internal speaker of the early versions had poor sound compared to the C64 and CPC - although later models of the Spectrum shared the AY-3-8192 sound chip with the CPC.

The Amstrad had superior graphical capabilities to the Spectrum, but many CPC games were ported directly from their Spectrum counterparts, resulting in a number of conversions that failed to take advantage of the CPC capabilities and thus hurt the machine's reputation.^{[citation needed]} Even when that was not the case, the majority of CPC titles lacked smooth scrolling due to programming complexities.

The CPC's 80-column display and large install base of disk users made the CPC a more convincing choice for non-games work.

The CPC has occasionally been described as an "improved Z80 implementation of the (earlier) BBC Micro"^{[attribution needed]} due to similarities in firmware and hardware. Both use the Motorola 6845 video address generator and the two have very similar sound output chips - the General Instrument AY-3-8912 in the CPC provides three tone channels each optionally with added noise and the Texas Instruments SN76489 in the BBC offers three tone channels and one exclusive noise channel. The BBC Micro uses an Intel 8271 floppy disc controller. The CPC uses the NEC µPD765A (Intel 8272), which is similar to the 8271 but contains the addition of a double density (MFM) mode.

The "two cursor" BASIC editing system seen on the Amstrad CPC (whereby holding Shift and using the cursor keys moves a shadow text cursor allowing text to be copied from another area of the screen to the normal cursor) is similar to that in BBC BASIC, albeit improved by allowing free movement of the normal cursor. Both systems provide similar systems of full hardware abstraction through operating system calls. This saves programs that do not require time-critical hardware access from having to touch the underlying machine and provides a level of machine portability for those programs.

Amstrad followed their success with the CPC 464 by launching the Amstrad PCW word-processor range, another Z80-based machine with a 3" disk drive and software by Locomotive Software. The PCW was originally developed to be compatible with an improved version of the CPC ('ANT', or Arnold Number Two - the CPC's development codename was Arnold). However, Amstrad decided to focus on the PCW, which in due course became vastly successful, and the ANT project never came to market.

On 7 April 1986 Amstrad announced it had bought from Sinclair Research "...the worldwide rights to sell and manufacture all existing and future Sinclair computers and computer products, together with the Sinclair brand name and those intellectual property rights where they relate to computers and computer related products." [3] which included the ZX Spectrum, for £5 million. This included Sinclair's unsold stock of Sinclair QLs and Spectrums. Amstrad made more than £5 million on selling these surplus machines alone. Amstrad launched two new variants of the Spectrum: the ZX Spectrum +2, based on the ZX Spectrum 128, with a built-in tape drive (like the CPC 464) and, the following year, the ZX Spectrum +3, with a built-in floppy disk drive (similar to the CPC 664 and 6128), taking the 3" disks that many Amstrad machines used.

Simple reprogramming of the Motorola 6845 CRTC can produce extended graphic modes, with up to 784×384 pixels, that use the overscan area - though these are not supported by Locomotive BASIC. Careful timing of palette switches allows all 27 hardware colours to be visible in any display mode. Due to high CPU use, programs with variable CPU load, such as games, would not usually change the palette more than six times per frame (the frequency of the CPC's hardware interrupt).

Changing the video address in mid-frame, which itself is only possible by fooling the CRTC into thinking that the end of frame has occurred, splits the screen in two separate areas that can be hardware-scrolled independently.

The custom VGA (Video Gate Array) chip could also be reprogrammed in the middle of the frame. Changing the display mode, for example, allows the programmer to divide the screen into a colourful playing area and a high resolution score area -- as in Sorcery by Virgin Games[4].

Careful programming of the AY sound chip could cause it to produce a level wave. Adjustment of the output volume would cause related adjustments in the amplitude of the wave. Using this observation it was possible to output PCM digital audio at roughly 5-bit quality, albeit at a very high CPU cost.

The machine had an internal mechanical relay for controlling the tape recorder's motor which when switched would produce an audible click. A very few pieces of software used this trick to produce "realistic" percussion sounds.

• Arnold (Windows / Unix / Linux / Mac): http://arnold.emuunlim.com
• Caprice (Windows / Unix / Linux): http://sourceforge.net/projects/caprice32
• Caprice (Gamepark GP2X): http://archive.gp2x.de/cgi-bin/cfiles.cgi?0,0,0,0,5,1174
• Copacabana (PalmOs / Windows): http://copacabana.emuunlim.com/
• CPCE (Dos / DPMI / Windows): http://cpce.emuunlim.com/
• CPC++ (Mac / Linux / Solaris): http://bricerive.free.fr/cpc/cpcpp.html
• WinAPE (Windows): http://www.winape.net
• WinCPC (Windows): http://www.wincpc.ch
• PC-CPC (Windows): http://amstrad.cpc.free.fr/article.php?sid=303
• CPCast (Dreamcast): http://ltk.dciberia.net/dreamcast/cpcast/cpcast.htm
• Pituka (Gamepark32): http://david.dantoine.org/contenido/4
• AMI-CPC (Amiga): http://home.nordnet.fr/~ldeplanque
• CrocoDS (Nintendo DS) http://deadketchup.kyuran.be/2007/01/12/crocods-v10/
• MESS (Windows / UNIX / Linux / Mac)

• TurboCPC core (terasIC T-Rex C1): http://www.symbos.de/trex.htm
• TurboCPC core (C-One): http://c64upgra.de/c-one/

• List of Amstrad CPC games
• Amstrad PCW (CP/M wordprocessor/personal computer range)
• CP/M
• Sinclair Research
• ZX Spectrum
• SymbOS (multitasking operating system)

• Amstrad official website
• CPC Wiki - user-edited reference to CPC hardware, software and folklore
• Amstrad ESP. All about Amstrad CPC in Spain
• The Unofficial Amstrad WWW Resource
• Amstrad CPC Imperium / Amsoft Headquarter
• The Amstrad CPC Games Resource
• CPC Game Reviews
• Amstrad Zone
• Amstrad CPC Info
• SymbOS Multitasking Operating System
• CPC/Amstrad support site run by Amstrad employee
• CPCScene Radio / Amstrad CPC music from games and demos
• WACCI.org.uk / UK user group providing Armstrad Support