464 - CPC UncoveredHardware Le Cpc 464
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Tucked away on eBay UK in April was a CPC464. Nothing special there, except that this one happened to be a grey-coloured prototype. Unassuming in appearance but rich in history, this CPC proved to be a very rare curio and an important part of Amstrad's past Richard Burton takes up the story... 

Not having heard of let alone seen this machine before, the slightly anonymous

looking grey Amstrad CPC464 offered up more questions than answers. It was listed as a prototype of the more colourful official release, but what made this machine particularly intriguing was the fact that it featured two motherboards and a different processor.

So we decided to have a sniff around to try and find out more about this oddity. With the help and boundless knowledge of Cliff Lawson at Amstrad, a software engineer who joined the company in 1984 and who has had a hand in almost every computer the company has released, the story behind the grey CPC464 came together.

We know that this anaemic-looking machine is a prototype, but what makes it so different from other CPC464S to warrant that label? Well, just about everything actually. As the incredibly alert will have spotted by now, the casing is light grey. This is what most obviously differentiates the prototype from the real production machine and these initial attempts at moulding the CPC casing are known as 'first shot* plastics. The injection moulder would make a tool for the casing and then run off some early samples in order to test the tool. Initially, the injection moulder would just be loaded with any plastic chips that happened to be to hand, so the casings were often cream or grey. Later, Amstrad would specify the exact livery and then buy in plastic chips to produce the required colour scheme.

Duel processor

So that's the outside dealt with, but what about the inside? Well, for starters it's got two motherboards, one stacked on top of the other. It was built in such a way that the upper board connected to the lower by the same 40 pins as the final chip would, so the lower board is effectively the final production version of the CPC motherboard and the upper board simulates the ULA (Uncommitted Logic Array) chip.

The auction listing also pointed towards a difference in processors. In the production version the processor was a Z80 , whereas the prototype CPC features a 6502 processor.

When Amstrad set out to make a home computer it saw how successful the 6502-based Commodore 64 was and basically said "We want something like that." Sir Alan employed a couple of graduate engineers who set about designing the machine. The pair told the industrial designers what keys they thought they would need on the keyboard and, in parallel, the cabinet/ keyboard was designed. This lead to the grey plastic casing.

The cabinet/keyboard was ready but the electronic/software designers were suffering delay after delay. Eventually the designers decided to call it a day and absconded, leaving Amstrad with a nicely tooled casing ready for production but no 6502-based PCB design or software to go into it.

By a rather roundabout route the technical director at Amstrad got in touch with a guy called Roland Perry, a Cambridge graduate who was apparently recommended as someone who "knows a bit about computer design." That turned out to be something of an understatement! Roland later became the namesake for a series of Amsoft's own software titles!

Amstrad asked Roland if he could co-ordinate the design of a computer to fill the void. Conveniently, he knew of a few other Cambridge graduates who had gone on to form hardware and software companies - Mark Eric Jones of MEJ Electronics, and Richard Clayton and Chris Hall of Locomotive Software. He quickly got in contact with them.

Locomotive already had a BASIC interpreter and it mainly produced Z80-based word processing machines. MEJ Electronics did the electronic design for Locomotive. Both companies told Roland Perry they could put together a BASIC home computer in six months, but only if it was a Z80 processor and not 6502-based, so they could re-use existing equipment.

The super-rare Grey Arnold was sold with the original user manuals

So Amstrad agreed to ditch the 6502 design and have a Z80-based home computer instead. It's incredible to think that in just six short months ME) designed the electronics and Locomotive honed the software that made the Amstrad CPC464 the machine we all know and love today.

Take a close look at the bottom of the motherboard - you can make out the Gate Array Simulator wording

As for the pre-existing keyboard, these were already tooled so Locomotive had to make the software work with the pre-defined layout, which is why that funny T key is used to access external commands -a little pointless, but it's a function nonetheless.

So what were the prototypes going to be used for? Development is the quick answer. The lead time on producing custom-masked chips, such as the ULA in the CPC, was many months, but Amstrad needed to have a supply of software titles available on the day of the CPC's launch. So, during development, just 50 prototypes were built with a Gate Array Simulator board fitted in place of the final ULA whilst it was still being manufactured.

Some of the prototypes were used internally at Amstrad for testing and development, but as soon as the firmware/BASIC was working, the machines were sent out to the main UK software houses. The idea was that they could port existing C64 and Spectrum titles to the CPC or cultivate new software to coincide with the official launch of the machine so that there would be an immediate software base from day one.

The developers were sworn to secrecy when given the prototype machines because the logic board effectively exposed the ULA design. The machines weren't supposed to be 'let out' because they could have been used to clone the CPC design - a nightmare scenario for Amstrad, which was attempting to break into the computer market for the first time. The ULA was always the clever bit of the Amstrad CPC and cloning it would have been a major concern back then.

Amstrad also ran a software testing competition for the new owners of the prototype CPCs. There was a £50 reward to anyone who could find a bug in Locomotive's firmware. No reward was ever paid out, which is a testament to the quality of Locomotive's software.

"The exact number of prototypes left in existence is unknown. Amstrad apparently purged its archives a while back and dumped several of the machines and the accompanying paperwork in a skip"

The production line CPC464, with its familiar dark grey casing and coloured keys

Lost and found

The prototype listed on eBay must have originally belonged to one of the software development houses. From there it somehow fell into the hands of one lucky seller, Nick Spencer.

Nick originally bought this machine for just £5. When the auction had finally run its course, the impressive final bid was for £620, which sent the machine winging its way to its new home in Madrid, Spain. The exact number of prototypes left in existence is unknown. Amstrad apparently purged its archives a while back and dumped several of the machines and the accompanying paperwork in a skip. Those lucky bin men...

RG#18 (2005)

★ YEAR: 1984
★ EDITEUR/DEVELOPPEUR: Amstrad Consumer Electronics

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L'Amstrad CPC est une machine 8 bits à base d'un Z80 à 4MHz. Le premier de la gamme fut le CPC 464 en 1984, équipé d'un lecteur de cassettes intégré il se plaçait en concurrent  du Commodore C64 beaucoup plus compliqué à utiliser et plus cher. Ce fut un réel succès et sorti cette même années le CPC 664 équipé d'un lecteur de disquettes trois pouces intégré. Sa vie fut de courte durée puisqu'en 1985 il fut remplacé par le CPC 6128 qui était plus compact, plus soigné et surtout qui avait 128Ko de RAM au lieu de 64Ko.