The CPC 464
Although they never reached the vast sales figures of the Sinclair Spectrum or Commodore 64, the CPC range of computers were well up there with a very loyal user base.
With the big two wrapped up in the games market, Alan Sugar entered the market with his eye on the serious user at a time when serious computers cost serious money.  Already famous for creating fully integrated, “single box” music systems at very low prices, Amstrad took the same approach with his computer project and produced the CPC 464.
Although an ugly beast (in some people's opinion), the system comprised a monitor, computer and integrated tape deck with a PSU housed in the monitor which powered the lot – very simple to set up and just one plug!  The real advantage for Amstrad by taking this approach was that it greatly reduced manufacturing costs.  The 464 sold for £200 with a green-screen monitor and £300 with a decent colour monitor - all at a time when a good monitor alone would set you back almost that! 
Add to that its ability to run CP/M when used with an external floppy disk drive and Amstrad had a winner.

The initial CPC 464 prototype (codenamed Arnold which gave the anagram "Roland" to several CPC games) had a 6502 processor at its core that was to be supported by 32Kb of RAM.  Amstrad decided to create its own BASIC language and contracted Locomotive Software to write an easy-to-use system.  Locomotive however favoured the speed of the Z80 and convinced Amstrad to change – a move which proved to be masterful in the future as Spectrum games were then very easy to port over as the Sinclair machines were built around the same processor.

Although initially launched as a serious machine, the 464 had 27 colours, 16 of which could be displayed in the lowest resolution mode and it had 64Kb of memory.  The integrated tape deck allowed for easy loading of software and as it also came equipped with a joystick port, all of which made it quickly popular with gamers.

However, it was not without its faults.  The machine was held back by a lack of hardware sprite capabilities, and the tapes were slow and unreliable (although this was common to all tape using machines of course).

Serious users were the bedrock of the machine’s sales as the CPC had a mechanical keyboard, a numerical pad and a cursor pad.  This couldn’t be said of the Commodore 64 and certainly not for the rubber-keyed Spectrum!

By 1985, things were going very well. Games released on the Spectrum and the Commodore usually found their way onto the Amstrad establishing as the third biggest player in the 8-bit market.  Ports from the Spectrum were easy, but often the programmers were lazy and didn’t take advantage of the CPC’s extra capabilities. The machine sold well in Britain and was also exported to France, Spain and Germany (where it was sold under the Schneider name).  In total, two million 464’s were sold throughout Europe.

CPC472 ? 

The CPC 464 was to be distributed in Spain by a company called Indescomp.

However, the Spanish Government believed that the machine would help promote English at the expense of Spanish, particularly as the tilde (-) was not present on the keyboard, so it put a tax on any computer with 64Kb or less that didn’t have the tilde. 

To play the system, an 8Kb module, which was completely unusable (but cheaper than changing the keyboard) was added to the machine to turn it into a 72Kb computer - the CPC 472 was born!

Of course the Spanish Government soon became wise to the move and put the tax on all computers without the tilde key.  Amstrad then had to change the keyboard, while keeping the extra 8Kb, resulting in two 472’s – one with and one without the tilde.  It was the only way to shift the stock they had made.

CPC664 

At the beginning of 1985, Amstrad upgraded the CPC 464 by restyling the cursor keys, updating Locomotive’s BASIC to version 1.1 and adding a built-in 3" disk drive to replace the tape deck. 

It ran under Amsdos (Amstrad Operating System), or CP/M 2.2 and the new model was named the CPC 664.  In Amstrad’s naming convention, the first number ‘4’ denoted a tape deck and the ‘6’ a floppy disk drive - the remaining digits referred to the RAM.  Again, this suited serious users as the machine now had a faster, more reliable way of storing data.  

However, memory was now becoming a problem - 64Kb was too small, certainly for business usage and in August 1985, less than a year after its launch, the 664 was killed off (making them quite rare and sought after by collectors these days).

CPC 6128
The replacement for the 664 was the 6128.  Again, running under Amsdos, CP/M 2.2 or CP/M+, the 6128 had twice the memory as the 664, the keyboard was made more compact without the gap between the keyboard and the numeric/cursor pads and the coloured keys were removed to make the machine look more professional.

For the gamers, the 6128 (as with the 664) was backwardly compatible with earlier models so that the vast catalogue of 464 software was almost fully supported. 

However, retaining the 664’s 3-inch disk drive was a mistake (ironically, the 664 was codenamed IDIOT - Insert Disk Instead Of Tape).  The disks held only 178Kb on each side and were a huge £3 to buy.  Very quickly, 3.5-inch disks were becoming the standard which held around 800Kb - all for only for only 50p.  Third parties created 3.5 inch drives for the CPC but no commercial software as released on the format.

For the next six years, the CPC 464 and 6128 sold steadily, but as Amstrad started to concentrate more on its PCW range and then its first PC compatibles, rumours started to circulate that they were about to drop the CPC range. 

The Plus range

In June 1990, Amstrad quashed those rumours and introduced the Plus range. 

Looking like the Atari ST and Commodore Amiga, the tape deck of the 464 and the disk drive of the 6128 were moved behind the keyboard and proper robust expansion ports were used to replace the old edge connectors (which ruled out the use of any of the mass of peripherals for the earlier models which used the edge connectors). 

The new machines were named the 464 Plus and 6128 Plus – the CPC branding was dropped.

With the PCW and early PC compatibles now established as Amstrads serious business tools, the Company now changed its focus completely to the games market with the Plus range.  Although based around the CPC, Amstrad added a cartridge port in a bid to take on the console market with a hybrid machine capable of performing in both markets.  Other improvements included smooth hardware scrolling, better sound and up to 16 colours could be used from a palette of 4,096.  There were also 16 hardware sprites, each 16x16 pixels.  The old joystick was replaced with console-style paddles.

As with previous model releases, Amstrad tried hard to guarantee the loyalty of its existing CPC fan base by ensuring that the 464 Plus and 6128 Plus were backward compatible with the older machines.  But there were two major let-downs - the 6128 Plus didn’t have a tape port, depriving its owners of access to cassette games and 464 Plus owners could not connect an external disk drive.

Unfortunately, it was not long before the console hit problems with development houses choosing the more popular Sega and Nintendo machines.  The end had begun for Amstrad’s 8-bit machine and within a couple of years; sadly the entire range was scrapped.