Amstrad CPC

The Amstrad CPC was a series of 8 bit personal computers produced by Amstrad during the 1980s and early 1990s

The acronym CPC stands for Colour Personal Computer, although it was also possible to purchase a CPC with a green screen (GT65/66) as well as a standard color screen (CTM640)

The first model was the CPC 464 and was introduced in 1984

It was designed to be a direct competitor to systems Commodore 64 and Sinclair ZX Spectrum

The CPC category was a success, selling more than 3 million during the life of the model

The most distinctive features that an Amstrad offered:

• Matte black casing with sharp corners and a narrow, rectangular shape (since it incorporated a cassette deck (CPC 464) or a floppy drive (CPC 664 and CPC 6128) )
• keyboard with special keys of distinctive colors (all non-standard keys on a typewriter)
• single power supply connection with one cable going from the console to the monitor (or RF modulator) and one cable going independently
• With an optional adapter, the monitor could be replaced with a television

Description

Amstrad initially presented the CPC as an improvement to the ZX Spectrum and of C64 because it was a complete system, including everything needed to use the equipment, all in the same package

Compared to a C64 o one ZX Spectrum, Amstrad CPCs included their own monitor, a built-in tape recorder or floppy drive, and even a small speaker

This formula of marketing gave a more attractive professional to Amstrad's CPC by marketing it in the same way as professional-oriented systems, rather than just gaming or home

Due to entering the European 8 bit market late, the CPC range never reached the sales volume of the ZX Spectrum or the C64

The advantages of its typewriter-like keyboard and built-in tape recorder or disk drive earned it a considerable market in the late 1980s

Despite strong competition in the United Kingdom, it became the most popular and best-selling computer in France at that time

CPC Family

Amstrad CPC 464, 472, 664, 6128

The original CPC was sold with the following configurations:

• CPC 464 Tape recorder, 64 KB RAM, square-edged keyboard
• CPC 472 Tape recorder, 72K RAM (although the extra 8K of RAM could not be used)
• CPC 664 3" floppy drive, 64K RAM, curved keyboard; short-lived model, quickly replaced by better specified 6128
• CPC 6128 3" floppy drive, 128K RAM (bank switching access), IBM PC like keyboard

External disk drives such as the DDI-1/FD-1 were available for the 464

A tape adapter was available for the 664 and 6128

All 128K models were compatible with the variants of 64K

A third-party hardware add-on, Multiface, enabled backup for most tape-to-disk software

Most games and software were released for the 64K RAM 464 and 664 models

Only a handful of titles were released exclusively for the machines of 128K

The system memory design allowed CPCs to run CP/M 2.2 and CP/M software, it was not uncommon to adapt it specifically for the machines

An Amstrad-specific variant of CP/M 3.0 (also known as CP/M Plus) was developed for the 6128 and used in later years

West Germany: Schneider CPC 464, 664 and 6128

Amstrad's German sister company Schneider produced its own CPC models 464, 664 and 6128

These machines used their own gray color codes instead of Amstrad's alternative color and a standard Centronics port instead of the expansion connector, but were identical at a hardware level

The documentation and the printed labels were translated into German

East Germany: KC compact

Like most other computers of this era, the CPC was inspired by Eastern Bloc clones; the East German-made KC compact used Soviet and East German components

The machine differed from a CPC visually with a different style of case, an external power supply and (optional and even more scarce than the main device) an external 5.25" Robotron disk drive

Unlike the Amstrad models, it could be used with an external television screen

It ran BASIC 1.1 and a clone of CP M 2.6, the German-language MicroDOS

It had 64K of built-in RAM, and 64K of additional RAM, which were provided by the external adapter for the tape drive/disk

The Z80 processor was replaced by a U880 (which was 100% compatible, including its bugs) and some proprietary Amstrad I/O chips were replaced with clones based on the Z8536 (which was 95% compatible with the original)

CPC 5512

The CPC 5512 It was a false and non-functional model invented by a French magazine; Its specifications included 512K of RAM, a 5.25" floppy drive, and a CPC 6128 clone GEM

PLUS models

In 1990, Amstrad introduced the series Plus modified the hardware in many ways and added a cartridge slot to all models

Most of the improvements were due to the video display, which saw an increase in its palette to 4096 colors and gained the ability to handle hardware sprites

Splitting the screen into two separate windows and pixel scrolling became features of supported hardware, although both features were possible to achieve with non compatible hardware Plus intelligently programming the existing Motorola 6845

An automatic DMA transfer system was also added to power the sound chip, although the chip itself remained unchanged

Additionally, the BASIC command set for disk access has been improved

A stripped-down CPC+, with no keyboard or cartridge-less media support, was released simultaneously as the GX4000 gaming console

Those models did not perform very well in the market as they failed to attract any third party support

The 8 bit technology behind CPC was starting to look a bit outdated by 1990 and users resented the substantial increase in prices on cartridge games compared to their disc and tape counterparts

Hardware Description

All CPC models were based on a Zilog Z80 processor with a clock speed of 4 MHz

Because a common set of RAM is shared with the video circuitry, the Z80 can only perform memory accesses every four cycles, which has the effect of rounding all instruction cycles up to the next multiple of four

The system came with 64 KB or 128 KB of RAM depending on the model (could be expanded to 512k)

The machines also featured a standard joystick socket in the style of Atari with 9 pins that could use two joysticks through a splitter

Video (graphics): modes, outputs

Basically the CPC video output used 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 recorded at a constant rate, so a 4 bpp display generated half the pixels every 2 bpp and a quarter every 1 bpp

The ROM included three built-in screen resolutions, but many others 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)

It supported a 27-color color palette, derived from the RGB color space with each component assigned as off, half on or on

The latest Plus models extended it to 4096 colors and added hardware sprite support

This hardware was similar to other 8 bit computers

In particular, the CPC lacked the color conflict of the ZX Spectrum and the intelligent programming of the 6845 could produce overscan, different resolutions (although with the same pixel density) and smooth pixel scrolling

The machine lacked an RF TV output or composite video output and was instead shipped with a proprietary 5 pin DIN connector for use exclusively with Amstrad monitors

An external adapter for RF TV you could buy separately

The DIN connector five-pin was able to connect to a tv SCART using the correct cabling

Audio (sound)

The CPC used the General Instruments AY-3-8912 sound chip, which provided three channels, each configurable to generate square waves, white noise, or both

A small range of hardware volume wrappers were available

Output was provided in mono by a small (4 cm) built-in speaker with volume control, driven by an unusually powerful amplifier

Stereo output was provided via a 3.5mm headphone jack, which was not present on some early CPC464 models

On those models, what looked like a standard 3.5" headphone jack was actually used to connect an external tape recorder, although later models used a five pin DIN connector for the same purpose

Playing digital sound samples at a resolution slightly better than 5-bit, as could be heard on the RoboCop game title screen, was possible through clever programming of the sound chip

This trick forced a lot of the processor and made it difficult to combine it with any other process

3" floppy drives

Amstrad's idiosyncratic choice of Hitachi's 3" drive, when the rest of the PC industry was using Sony's 3.5" format, was often due to Amstrad purchasing large numbers of 3" drives in Asia

The single-sided drive (incorporated in later models) was 40 tracks and required the user to physically remove it for access to the disk on both sides

Each side had its own independent switch for write protection

The sides were designated “A” and “B”, each containing 180 KB (178 KB in AMSDOS format) for a total of 360 KB per disk

The interface to the drives was an NEC 765 FDC, used for the same purpose on the IBM PC/XT, PC/AT and PS/2 machines

Many of its features were not used to reduce costs, such as DMA transfers and support for single-density disks; was formatted as double density using modified frequency modulation

The discs were kept in a paper sleeve or a hard plastic case that resembled a compact disc “jewelry” box

The case was thicker and stiffer than the 3.5" floppy disks, and the sliding metal cover to protect the media surface was internal to the case and latched, unlike the simple external sliding cover on the Sony version (some articles of the time stated that they did not cause problems)

Therefore, they were significantly more expensive than the 5.25" and 3.5" alternative

Combined with its low nominal capacities and essentially proprietary nature, it caused the format to be discontinued when the CPC was discontinued

In addition to the 3" Amstrad machines (PCW and ZX Spectrum +3), the only other computer systems to use them were the Sega SF-7000 and the mostly unknown and exotic CP/M systems such as the Tatung Einstein and Osborne machines

The data format of the 3" disks was very similar to that of the 5¼" disks, and the Amstrad CPC machines could use 5¼" drives through their “external port”, either one specially designed for the CPC or by an IBM-PC adaptery

A very popular alternative was to connect an IBM-PC 3½" drive adapted to operate in 180 KB single-sided or 360 KB double-sided mode, although thanks to the later availability of the STOPPED Disk Operating System, 720k per disk was available

Adapter from serial port

An official RS-232-C D25 serial port adapter was made, which connected to the expansion connector on the back of the machine and had a connector for the CPC464 disk drive or other peripherals

The adapter came with a "Book of Enchantments" to facilitate data transfer between other systems that use a proprietary protocol in the device's own ROM, as well as terminal software to connect to British Telecom's Prestel service

We created a separate version of the ROM for the us market due to the use of the commands SUCK and BLOW, that were considered unacceptable

Similarities with the Micro-BBC

The CPC has been called an “enhanced Z80 implementation of the Micro BBC (previous)” due to similarities in firmware and hardware

Both used the Motorola 6845 video address generator and both had very similar sound output chips: the General Instrument AY-3-8912 in the CPC provided three tone channels, each with optional additional noise, and the Texas Instruments SN76489 at the BBC offered three tone channels and a dedicated noise channel

The Micro BBC used an Intel 8271 floppy disk controller

The CPC used the Intel 8272, which was similar to the 8271 but contained the addition of a dual density mode (MFM)

The “two-cursor” BASIC editing system seen in the Amstrad CPC (whereby holding down the Shift key and the cursor keys moved the shadowed text cursor allowing the text to be copied from another area of ​​the screen to the normal cursor) was an addition to BBC BASIC

Although it was a substantial improvement by allowing free movement of the normal cursor

Both systems provide a total abstraction of the hardware through calls to the operating system

This prevented programs that did not require time-critical hardware access from having to touch the underlying machine and provided a level of machine portability for those programs

Software

Operating system and Built-in BASIC

Like most personal computers of that era, the CPC had its operating system and a BASIC interpreter built into its ROM

Used Locomotive BASIC, a variant specifically written for CPC hardware that, as a result, was faster, more comfortable, and more powerful than the generic Microsoft BASIC commonly used by Commodore 64 and MSX, among other

It was particularly notable for providing easy access to the machine's audio and video resources in contrast to arcane commands POKE required in some Microsoft implementations (the implementation MSX of Microsoft Basic was an exception, which even allowed hardware sprite manipulation and collision detection)

Other languages

Although it was possible to obtain compilers for Locomotive BASIC, C and Pascal, the majority of the software of the CPC was written in assembly language native to the Z80a

An interpreter for educational language LOGO was also available

CPC Software Review (Games)

The quality of CPC software has sometimes been criticized due to the existence of games that were simply conversions of the ZX Spectrum, so it was not similar with the equivalent implementations of the ZX Spectrum or C64 in terms of maximum use of the capabilities of the CPC

Because the CPC shared the Z80a processor with the ZX Spectrum, and could be made to run the same code using similar display modes, many game makers developed their games for the two systems in parallel or by converting games from Spectrum old, producing products that did not take advantage of hardware scrolling or the availability of 4 and 16 color modes

Despite this, the conversions of ZX Spectrum did not show conflicts with the capacity of the CPC

The CPC actually had several problems to point out, such as the lack of hardware support for sprites and scrolling (long ago it was believed impossible to do this without creating problems in the vertical direction) and the complicated memory layout

This made the creation of games fluid and colorful outside more difficult

Titles from the late '80s onwards were more carefully coded than their mid-'80s counterparts, making better use of the machine's graphical capabilities

Such as smooth scrolling and better use of color

Games with poor scrolling, the almost monochromatic graphics of the Spectrum and slow control, especially at the beginning of the CPC's commercial life, were sold along with others, such as smooth scrolling, colorful graphics and crisp music and sound effects that almost rival those of the C64

Although the machine received more software support than most other Z80-based systems, the overall impression left is that it could have been more commercially successful

That said, it is important to highlight that the numerous software companies of that time, such as Ocean Software, Elite Systems, Palace Software, Incentive, Hewson Consultants, Loriciels or Dinamic Software, among others, released quality titles on a regular basis that kept CPC users more than happy with their color personal computer

Amstrad CPC vs Competitors

Since the Amstrad CPC was built specifically to compete with the ZX Spectrum and the C64, and which entered the 8 bit personal computer market relatively late in the 80s, comparisons between these computer systems were very frequent in specialized magazines, but also among the users themselves

Additionally, all three machines were compatible with virtually all 8 bit PC software in history, and had a virtually identical selection of games, albeit with major differences in quality, technical features, and platform dependent features

Amstrad vs C64

In general, users of C64 They were likely to dismiss both competing machines as “grossly inferior”

In fact, the C64 It had better sound, graphics and scrolling than its competitors, thanks to its dedicated hardware

In particular, its sound generating capabilities were superior, due to its SID chip

The C64 had a wide selection of games designed to run from floppy disks, although its floppy drives were much slower

He also suffered for a poor BASIC built-in and was not ideal for users who wanted to learn programming compared to the other two machines

Amstrad vs Spectrum

There was great rivalry between users of ZX Spectrum and those of CPC

The former considered that the CPC was just an overrated clone of their beloved Spectrum, while those of the CPC considered those of the ZX Spectrum like “poor and jealous cousins” who stained their beloved machine with inferior game conversions

The ZX Spectrum It had the simplest hardware of the three, although this translated into lower costs

As a result, the colors suffered and the internal speaker of the 48k versions had a very poor sound compared to the C64 and the CPC, although later models of the ZX Spectrum shared the AY-3-8192| sound chip with CPC

Many third party peripherals and some aspects of their BASIC built-in made it more attractive to DIY enthusiasts and hobby programmers

The Amstrad CPC had better graphics capabilities than the ZX Spectrum, but many of their games were direct conversions of the ZX Spectrum in terms of graphics and sometimes sound, resulting in a long series of low-quality titles that damaged the machine's reputation

Even when that was not the case, CPC titles rarely featured smooth scrolling or sprite handling due to the complexity of their programming, even if it was technically possible

After Amstrad

On April 7, 1986, the company purchased Sinclair Research, discontinuing the failed 16 bit Sinclair QL business machine and relaunching the 128KB Sinclair Spectrum in “+2” and “+3” variants with better keyboards and built-in storage

The housing and its design are distinguished from the CPC series

The company produced a range of inexpensive personal computers based on MS-DOS and later Microsoft Windows, the first of which was the PC1512 for £399 in 1986

It was a success, capturing more than 25% of the European market

A year later, in 1987, it launched the PCW 8512 as a dedicated word processing computer at a price of £499

In 1988 he attempted to make the first portable personal computer with the PPC 512/640, introduced a year before the Macintosh Portable, at 8 MHz it ran MS-DOS and GEM with a variant of the CGA video card that allowed GEM to display graphics in 16 colors

In the early 1990s Amstrad began to focus on laptops rather than desktops

It also attempted to enter the game console market with the Amstrad GX4000, similar to what Commodore had done with the C64 y el C64 GS

The machine was a commercial failure, being unpopular because it used 8 bit technology compared to the 16 bit technology of the Sega Mega Drive and the Super Nintendo.

Launches an IBM PC/Sega Mega Drive compatible hybrid, the Amstrad Mega PC, an Amstrad PC73864​ in which the AdLib sound card is replaced by an ISA board with the hardware of a Sega Mega Drive 1, with a PC Joystick connector and headphone minijack on the back and cartridge slot and two Mega Drive gamepad connectors on the front

But the good idea is a failure when choosing an already obsolete CPU and the set being more expensive than buying the two devices separately

In 1993 Amstrad launched the PenPad, a PDA similar to the Apple Newton released just a few weeks earlier

It was also a commercial failure, suffering from several technical and usability problems and lacking most of the features included in the Apple Newton, although it had a lower price (around $450)

During these years it also launched several models of music systems, with a plate for records and a double deck in a pack integrated with the furniture

It stood out for its low price and was one of the first to incorporate the double deck into the market

Another innovative product was the launch of a 14″ TV screen that included VHS video, and a VHS player that incorporated two units (in the style of double-deck radio cassettes)

As Amstrad began to focus more on communications and less on computers, it bought several telecommunications companies including Betacom, Dancall Telecom, Viglen Computers and Dataflex Design Communications

Amstrad has been a major supplier of television receivers to British satellite television operator Sky since its launch in 1989

Amstrad was instrumental in Sky's implementation, as it was the only manufacturer capable of producing receivers and satellite dishes at the time of the system's launch, and has continued to manufacture receivers for Sky, from analogue to digital, and now includes the digital video recorder for Sky+

In 1997 Amstrad supplied receivers to the Australian operator Foxtel, and in 2004 to the Italian Sky Italia

In 2000 Amstrad launched the first of its devices that combine telephony and email, called e-m@iler

It was followed by the e-m@ilerplus in 2002, and the E3 Videophone in 2004

Amstrad also produced a variety of home entertainment products throughout its history, including audio sets, televisions, VCRs, and DVD players

Following the success of the British version of The Apprentice series, Amstrad has also begun producing audio-animatronics

In July 2007, BSkyB announces the purchase of Amstrad for £125m

BSkyB has been Amstrad's main customer, representing 75% of sales in its Set-Top-Boxes sector

Amstrad has been a BSkyB supplier since 1988

On July 2, 2008, Alan Sugar stepped down as president of the company

Hardware tricks in the CPC series

CRTC Programming Tricks

Simple reprogramming of the Motorola 6845 CRTC could produce extended graphics modes, with up to 784x384 pixels, using the overscan area

Careful timing of the paddle switches allowed all 27 hardware colors to be visible in any display mode, but due to high CPU usage, programs with variable CPU load, such as games, could be limited to change palette once or twice per frame

CRTC parameters could also be changed while drawing a particular scanline of a frame, a technique with many applications

Changing the display mode in the middle of a frame allowed the screen to be split, for example, into a colorful game area and a high resolution scoring area, as in Sorcery by Virgin Games

Changing the video direction mid-frame, which was only possible by tricking the CRTC into thinking vertical sync had occurred, dividing the screen into two separate areas that could be hardware scrolled independently

Sound Tricks

Careful programming of the AY sound chip could cause the wave level to change

The adjustment of the output volume caused related settings in the amplitude of the wave

With this observation, it was possible to output PCM digital audio with a quality higher than 5 bits, although at a very high CPU cost

The machine had an internal mechanical relay to control the tape recorder motor which, when switched, produced an audible click

Some software programs used this trick to produce “realistic” percussion sounds, but usually such abuse of the relay caused it to fail prematurely

Magazines

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

Amstrad Community

Currently you can find active communities in spanish such as Amigos y Usuarios de Amstrad or Amstrad España