amstrad cpc

The Amstrad CPC was an 8-bit home computer produced by Amstrad in the 1980s. 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 machine was designed to be a direct competitor to the Commodore 64 and Sinclair ZX Spectrum systems. 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), and the unique power supply hookup with one lead going from the console to the monitor (or RF modulator) and one lead going the other way. A television could be used with an optional adapter.

The Amstrad CPC sold as a "complete system"

Amstrad, at least in the beginning. adopted an apparently smart motto for promoting CPC sales, which roughly went: "the Amstrad CPC is sold as a complete system, you need to buy nothing else after you open the box". This was, in fact, true to a large extent. Compared to a C64 or a ZX Spectrum, the Amstrad CPC's were always shipped with their own monitor, had a built in tape recorder or floppy disk drive, and even a small loudspeaker, resembling, in a certain manner, the way IBM-PCs and compatibles were marketed. This marketing strategy was probably chosen to give 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.

CPU and memory

All CPC models all featured a Zilog Z80a processor at about 4 MHz, 64KB or 128KB of RAM depending on the model, a palette of 27 colours (quite extensive for its time, most competitors having 8 or 16 colours), three display modes which could be mixed, stereo sound, joystick socket, standard printer connectors and an integrated cassette tape deck for program and data storage. As a general-purpose machine, its graphic chip lacked support for hardware sprites, unlike the more games-oriented American devices from Commodore and Atari.

Video and Graphics

All CPC models (except for the Plus series) featured the same graphics chip, a Motorola MC6584 graphics processor called CRTC (Cathode Ray Tube Controller), identical to the one found on CGA adapters, and had a number of standard video modes as well as many tweaked modes including overscan, multiple resolutions, graphic windows, HAM etc. The standard video modes (also directly accessible by the built-in BASIC) were:

Mode 0: 160x200 pixels with 16 colors (4 bits per pixel)
Mode 1: 320*200 pixels with 4 colors
Mode 2: 640*200 pixels with 2 colors

The total color palette was of 27 colors (4096 on Plus models) of which any combination, within the color limits of each mode, could be chosen. Compared to e.g. the ZX Spectrum the CPC's graphics didn't suffer from color clash, since the color resolution matched the actual resolution, but many games, especially Mode 1 games which were direct Spectrum ports actually looked the same (if not worse), on the CPC, since the resolution was different (320x200 instead of 256*192), the aspect ratio wasn't the same, and the CPC was limited to 4 colors in this mode, while the ZX Spectrum could actually display 8 or 16, save for the color clashing problem. In fact, most games which had a monochromatic action screen on the ZX Spectrum (such as Airwolf II), were implemented in Mode 1 and were also monochromatic on the CPC, though there were notable exceptions, especially in games made from 1989 and after, like The New Zealand Story, which was implemented in Mode 0. Compared to the C64's graphics, Mode 0 was practically on the par with the typical C64's resolution, barring different sprite resolutions and hardware scolling/sprites, which were the CPC's main weakness although games with smooth scrolling and multiple sprite handling appeared on the CPC too after 1989. The graphics output was another notable difference with most competing systems of the time, including IBM PC's: while most of its competitors had either RF TV or Compostie Video outputs and hooked directly to a normal TV or Video monitor, all Amstrad CPC models had got a fully analog 5-pin RGB DIN connector and came with their own RGB or Green monitor, which could provide, in theory, superior picture quality and sharpness. It was even possible to hook a CPC to a TV via a SCART adapter in RGB mode. The downside of this approach was that the user was bound to using only Amstrad's monitors, which in turn could only be used with the CPCs, barring of course any modifications and adaptations.

Audio and Sound

Another interesting aspect of the Amstrad CPC were its sound capabilities. While the sound chip was a - rather commonplace, at the time - Yamaha AY-3-8912, in general considered inferior to the C64's sound chip (SID), it was far better than the IBM-PC's and early ZX Spectrum's beeper and was configured as to give stereo sound through a built-in 3.5 mm headphones jack, unlike most other implementations and 8-bit home computers which only had mono sound. In any case, all CPC models had got a small (4 cm) built-in loudspeaker with volume control, which was however driven by an unusually powerful amplifier and gave the CPC a very distinctive and sometimes annoying sound. Playback of 8-bit or 4-bit Digital Sound samples was also possible, with the most notable example being the game Robocop, at least in its disk-based version for the CPC6128 model, one of the few games actually using all 128KB of RAM.

Built-in BASIC and Operating System

Like most home computers at the time, the CPC had its OS and a BASIC interpreter built in (i.e. in ROM). Locomotive BASIC was faster and more powerful than the commonly used Microsoft BASIC of the time. The Z80a assembly language could also be used, or later the optional Locomotive Basic Compiler. Most models could run CP/M and also use additional languages such as C, Pascal and LOGO.

Criticism of CPC's software

Because the CPC shared the Z80a processor with Sinclair Research's ZX Spectrum, some games manufacturers developed games for the two systems partly in parallel or ported older Spectrum games to the 464, and even to the more powerful 6128. This practice was often criticised, as resulting products frequently did not take advantage of the CPC's marginally faster processor and markedly superior graphics and sound. Overall, the quality of CPC software has been frequently criticized as being rather low compared to the machine's potential, and usually didn't measure up to the equivalent ZX Spectrum or C64 implementations. Reasons for this were partly explained because of the aforementioned ZX Spectrum ports, and partly because of the lack of hardware support for sprites and scrolling, which made the creation of smooth-running and colourful games hard though not impossible. Late (1989-1992) titles tended to be coded more carefully than their mid 80s counterparts, making better use advantage of the machines graphics capabibilities, featuring smooth scrolling and better color usage, but the CPC machines were already a dying breed when this finally occured. Although the machine received more software support than other Z80-based systems like the MSX computer series, the overall impression left is that said support could have been a lot better, in most cases, and the commercial success of the system could have been completely different. In fact, only a handful of game titles, such as Gryzor or Turrican can be said to have taken full advantage of the system's capabilities, let alone taking it "to the edge", like it was common with many C64 and ZX Spectrum titles.

CPC Models

The CPC model names were structured as follows: The first digit was a code for the main storage system; '4' denoted a tape deck and '6' a 3-inch floppy disk drive. The remaining digits described the RAM capacity. Thus:

CPC 464 – Colour Personal Computer, Tape Deck, 64K RAM, squarish keyboard
CPC 664 – Colour Personal Computer, 3" Floppy Disk Drive, 64K RAM, bowed keyboard
CPC 6128 – Colour Personal Computer, 3" Floppy Disk Drive, 128K RAM (bank switching), more PC-style keyboard.

Successor models in the CPC series were the Amstrad CPC 664 and Amstrad CPC 6128, both of which featured a 3-inch floppy disk drive in place of the 464's tape player (among other differences). External disk drives were available for the 464 (and its successors, for that matter), such as the DDI-1/FD-1 set (interface module and disk drive). With a disk drive in place the 464 could run CP/M 2.2, and some adaptations of CP/M software were done for the machine. The later CPC 6128 would run CP/M Plus (CP/M 3.0). The CPC 664 proved short-lived, quickly replaced by the better-specified CPC 6128. However, a rare CPC 472 (72KB RAM + tape drive) was produced in small numbers for the Spanish market, in hopes of avoiding a legal instruction to produce a Spanish keyboard. The three models were generally compatible, as the 6128 and 664 could generally load cassette-based 464 software through a special adapter, or run cassette games dumped on floppy disk via a unit called the Multiface, although a handful of games could malfunction due to copy-protection or because of using 464-specific system functions, which limited compatibility. Viceversa, the 464 model could load floppy disk-based software through the use of an external floppy disk drive or through cassette dumps, again with some minor risk of incompatibilities. However, compatibility was not generally a problem since most games and software were designed with the 464 and 664's limitations in mind (especially the 64KB of RAM) and only a handful of titles were specifically designed to take advantage of the CPC's 6128 extra amounts of RAM, another factor which made the overall CPC's software scene appear somehow lacking compared to its direct competitors.

Licensed manufacturers

Amstrad's German partner company Schneider produced its own models of the CPC 464, 664 and 6128. These are essentially the same all replace the coloured keys on the keyboard with grey ones and Amstrad's cheap motherboard edge connectors with industry standard Centronics ones. Documentation and even case labels were also all translated into German. Other CPCs was produced for the multi-language european market, for Spain or France. They often but not always came along with a localized keyboard.

Hardware Clones

A rare cousin of the CPC is the KC-compact, made in GDR using Russian and East German chipsets. With a different style of case, external power supply, connections for a television screen, external 5.25" Robotron disc drive and a few strange power features on the standard interfaces, it doesn't look like a CPC at first sight. It runs BASIC 1.1 and also a CP/M 2.6 clone, the German speaking MicroDOS. It has 64K RAM, plus an additional 64K RAM is provided with the external disc/tape drive adapter. The Z80 processor was replaced with a U880, and some proprietary Amstrad I/O chips were replaced with clones based on the Z8536. This clone machine is around 95% compatible with the original CPCs. Another very strange thing was the CPC 5512, a non-functional fake made by a french magazine. 512K RAM, 5.25" floppy disc drive and GEM on a CPC 6128 clone Z80a. Nice. Nuff said :-).

The 3" floppy drive

Amstrad's idiosyncratic choice of Hitachi's 3" floppy disc drive, when the rest of the PC industry was moving to Sony's 3.5" format, is often claimed to due to Amstrad bulk-buying a large consignment of 3" drive units in Asia. The discs were reversible; in the cheapest drive, a single-sided 40-track unit, the disk could be removed and re-inserted into the drive the other way up. Something similar could be done with 5.25" discs in some drives, but this required cutting a separate second write-protect notch. Some "hard-sectored" drives even required the punching of a second sector-0 locating hole in the floppy's casing. The sides were termed "A" and "B" and were completely independent but the drive unit could only access the upper side at one time. Each side held 180KB for a total of 360KB per disc. Unlike 5.25" or 3.5" disks, the 3" discs were designed to be reversible and sported 2 independent write-protect switches. The casing is thicker and more rigid than that of 3.5" diskettes and 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. Disks were shipped in a paper sleeve or a hard plastic case resembling a Compact Disc "jewel" case. In mechanical design they were arguably superior to 5.25" diskettes but they were significantly more expensive than both 5.25" and 3.5" disks, due to their complexity. This, combined with their low nominal capacities and their essentially proprietary nature, lead to the format being discontinued when the CPC itself was discontinued. Apart from Amstrad's other 3" machines (the PCW and Spectrum +3), the only other computer systems to use them were mostly obscure and exotic CP/M systems such as the Tatung Einstein and Osborne machines.

Optional 5¼ floppy drive

The data formatting of the 3" disks practically reproduced that of the larger 5¼ disks on a smaller scale, and in fact the Amstrad CPC machines were able to use an external 5¼ drive through their "external drive" port, either one specially designed for use by the CPC, or an adapted standard IBM-PC 5¼ drive, thus leading to some partial data exchange possibilities with IBM-PCs and the chance of using cheaper disks and more easily replaceable drives. Similarly, an adapted IBM-PC 3½ drive could be attached externally and be operated in either single-sided 180KB or double-sided 360KB mode, but this never really caught on as much as 5¼ drives.

Additional features in later models

Some later models had extra functions built into BASIC, an enhanced colour palette and a read-only cartridge system. Extra BASIC functions were also built into the DDI-1 disk drive interface, allowing the CPC 464 user to access the AMSDOS disk operating system, and thus the disk drive(s), through BASIC. The final models in the CPC range were the CPC464+ and CPC6128+ and the ill-fated GX4000 video game console. The latter was a massive commercial failure, not least due to limited game releases from other companies; Amstrad's in-house software division Amsoft couldn't fill the need. Magazines available for the system (at various times) included Amtix, Computing With The Amstrad, Amstrad Computer User (Amstrad official publication), Amstrad Action, and CPC Attack. Notable games include Bloodwych, the Rick Dangerous, Turrican and Dizzy series, and Head over Heels. As a relatively late entrant to the European 8-bit market, the the CPC range never achieved the penetration of the Sinclair machines, despite superior - albeit more expensive - hardware. As hardware prices fell, Amstrad's higher-specification style of machine, with proper typewriter-style keyboards and integral tape or floppy drives, became more affordable. Ultimately, the company purchased Sinclair Research, discontinuing the unsuccessful Sinclair QL 16-bit business machine and relaunching the 128KB Sinclair Spectrum in "+2" and "+3" variants with better keyboards and integral storage. The case and design of these recognisably drew from the CPC series.

Advanced programming and hardware techniques on the CPC series

Despite the lower popularity of Amstrad CPC series, compared to the ZX Spectrum and the hardware-tricks filled C64, the Amstrad CPC had got some notable hardware tricks of its own, with the most common being video overscan modes and extended graphics modes up to 784*384 pixels with all 27 colors visible, used mainly in demos. Also, most games could actually use more than 4 colours in graphics mode 1, through a simple HAM technique (a technique also used by a handful of PC games in CGA modes). Interestingly enough, the graphics chip in early (non-plus) models was the MC6584, the same one used on IBM-PC and compatibles CGA graphics adapters, although the CPC monitor was fully analog and better-suited for multiple resolutions and greater color depths than the typical digital CGA monitor. Also, in any graphics mode, the Amstrad CPC allowed unlimited use of all palette colors, unlike CGA implementations which could only use fixed-color palettes. On the other hand, the typical PC/MS-DOS high resolution text modes were either unavaiable or uncommon on the Amstrad CPC. A less common hardware trick was quickly activating and deactivating an internal mechanical relay meant for controlling the internal or external tape recorder's motor, thus producing an audible percussion-like sound. Some demos actually used this trick to produce "realistic" percussion sounds, but usually such an abuse of the relay resulted in its early failure.

Amstrad Cpc