The day after Richard Altwasser left Sinclair Research, the company had to advertise for “the world’s best computer designer” to replace him. He talks to Brendon Gore about the development of Sinclair’s exciting new colour computer.
Occasional windsurfer, sometime engineering graduate and full-time microcomputer enthusiast, Richard Altwasser was largely responsible for the development of the hardware for the Sinclair ZX Spectrum. Together with Steven Vickers, who wrote most of the ROM for the Spectrum, he was in on the launch of Sinclair’s latest microcomputer from the very beginning.
Richard Altwasser graduated from Trinity College Cambridge with an honours degree in engineering in June 1978. Originally, he had planned to take up a lecturing position at a university in the Phillipines under the aegis of the VSO. But, in the end, he decided to get married and stay in the U.K.
After writing to 19 different companies, and being offered four jobs, he decided to join Metal Castings in Worcester. As the head of a small electronics team, he was responsible for installing industrial robots and for designing the company’s own programmable-control and instrumentation equipment. It was, he says with just a touch of understatement, quite a novel field for electronics.
A Swedish friend first introduced Richard Altwasser to microcomputers. On his recommendation, Altwasser bought a Tandy TRS-80 and soon became hooked on the microcomputing bug. He also realised that microcomputers had potential for the work he was doing for Metal Castings.
“I demonstrated a few programs to some of the directors and persuaded the company to buy a TRS-80. I ran a short evening class for the engineers to teach them how to use the thing, and I think it proved quite useful to them”.
But Richard Altwasser had become increasingly disenchanted about his career prospects with Metal Castings. The company was closely linked to the automotive industry which had suffered serious setbacks during 1979 and 1980. Con¬sequently, the company seemed more interested in cutting back its production facilities than in developing them.
Altwasser started looking around for another job. An advertisement in the national daily press caught his eye — Sinclair was looking for an electronics engineer. This seemed an ideal opportunity, as Sinclair had made its first real venture into the microcomputing market with the launch of the ZX-80 a few months previously.
Two interviews followed Altwasser’s application to join Sinclair. The first was conducted by a company of recruitment professionals. It consisted of a number of in-depth personal and technical interviews including an intelligence test and a personality profile to determine whether he was an introvert or an extrovert.
The second interview was with Clive Sinclair at Cambridge. “He invited me into his room where he had a ZX-80 and sort of ushered me to sit down”, says Altwasser. “After sitting in silence for a few moments I thought I had better do something, so I started writing a little program on the ZX-80 which sparked off a bit of conversation. After a few minutes he offered me a job and I accepted it. We shook hands and that was it”.
Richard Altwasser joined Sinclair on the first Monday in September 1980. He was immediately informed of two things. Firstly, Sinclair’s 8K ROM, and 16K RAM pack were about to be launched. Secondly, he was told that the chief engineer was going on holiday so it was up to him to write some programs to demonstrate the capabilities of the new ROM and RAM pack.
Not surprisingly, Altwasser worked late on his first day at Sinclair. It was a pattern that was to continue for the next two years.
“People who work for Sinclair do not have many hobbies”, says Altwasser ruefully, “they tend to work too much”.
Plans for the ZX-81 were well advanced by the time Altwasser joined Sinclair. His main contribution to the ZX-81 was designing its printed-circuit board. This brought him into contact with one of the policies that differentiates Sinclair from its rivals.
“It is a policy of Sinclair not to employ technicians”, explains Altwasser. “Whereas a lot of companies employ people to draw up circuit diagrams that engineers have scratched on the back of cigarette packets, and maintain a myriad of support staff, Sinclair believed in employing engineers and letting them do all of these support tasks. So I spent a lot of time with a soldering iron literally soldering things together, building up prototypes for the ZX-81″.
After the launch of the ZX-81, Richard Altwasser was made respon¬sible for computer development. It was a move that led directly to the birth of the Spectrum. The idea was first conceived towards the end of July, 1981. Lengthy discussions between Altwasser and other Sinclair engineers resulted in the drawing up of broad specifications for the next generation of computer. “We decided it must have high-resolution graphics, probably 16K of memory, an improved cassette interface, sound and of course most importantly colour”.
“One of the first questions that we had to ask ourselves was about the display mechanism”, reveals Altwasser. “On the ZX-81, the CPU is part and parcel of the display — the CPU program counter is used as the memory-address register. This means that the slow mode on the ZX-81 is the only continuously moving graphics mode and that has a CPU efficiency of only 25 percent. So we had to decide whether to continue with that sort of approach or to divorce the CPU from the display are to enable it to work at full efficiency.
“We felt that with a computer that was going to have high-resolution graphics as well as colour, people would want to have fast-moving animated displays. Consequently, we decided to design a computer architecture that divorced the CPU from the display”.
The next problem that Altwasser faced was how to include colour in the display. The first idea that he considered was a derivation of the teletext approach where each line of text has colour change codes inserted into it. But, while this only use a limited amount of memory, it had the disadvantage of using up a character position every time the colour needed to be changed. In addition, while this approach was suitable for graphics and teletext displays, it was not suitable for high-resolution graphs or diagrams that involved multiple colour changes.
After much head scratching, Altwasser and his fellow engineers came up with the idea of allocating a colour attribute to each character position on the screen. This used six bits of memory, three bits to provide any one of eight foreground colours and three bits for the eight background colours, for each character position. With two bits of memory still available, Altwasser decided to include a flashing mode and a highlight feature that offered two levels of intensity.
This system took up slightly less than 7K of memory, which fitted in with Altwasser’s plan for a computer with 16K of dynamic RAM. The user was left with 9K of memory in which to write programs — a figure which Altwasser regarded as quite respectable.
The need for an improved cassette interface was all too clear from the number of ZX-81 users who encountered problems when trying to save and load programs. “The ZX-80/81 used a tone-burst mechanism that transmitted bursts of cycles at about 3kHz”, says Altwasser. “Nine cycles represented a 1 and four cycles represented a 0. But in the Spectrum one cycle represents a 1 and a half a cycle represents a 0, which works out faster as fewer cycles are used.
‘The second thing we did was to introduce a leader — that is a period of constant tone which allows the cassette recorder’s automatic gain control to settle itself down. In addition, we included a Schmitt trigger inside the Spectrum ULA. This helps to eliminate noise and hiss on the tape”.
Richard Altwasser was also involved in the preliminary stages of development the ZX Microdrive, which he regards as an achievement that is at least significant as the Spectrum itself. The ZX Microdrive can store up to 100K on a micro¬floppy disc, has a transfer rate of 16K a second and costs just £50. But Altwasser was unwilling to give away any secrets. His loyalty to Sinclair says much for both men.
The decision to call new machine the Spectrum and not the ZX-82 that many people had expected, was made for a number of reasons says Altwasser. “Firstly, the ZX-81 replaced the ZX-80 and the Spectrum is meant to run alongside the ZX-81 rather than replace it. Secondly, calling the Spectrum a ZX-82 creates the impression that the company will be producing a ZX-83 in the spring of 1983″.
Overall, Altwasser is very pleased with the finished Spectrum, it has more than lived up to its original specifications. “It is going to sound very partisan, but as this project came together I think we were all more impressed with it than we expected to be. We started off thinking that we were developing an enhanced ZX-81, but we ended up with a new, much more advanced, creature. I was particularly pleased with the tape mechanism — we originally aimed at getting it to work at about 1,000 baud, but we succeeded in making it work at 1,500 baud which is considerably faster. I think the weaknesses of the ZX-81 were its keyboard and its lack of memory. The Spectrum has quite clearly overcome both of those problems”.
Altwasser believes that the Spectrum is superior to rival machines such as the Vic-20 and Atom, but he has considerable respect for the BBC Micro. “I think there is no getting away from it, the BBC Micro is a very good machine that offers a wide range of facilities. But I do not think the BBC Micro is as friendly or easy to use a computer as the Spectrum. I think behind the Vic-20 is a very good advertising company backed up by a second-rate computer. Both the graphics and the sound are limited by the Vic-20′s internal ROM software which is not really designed to deal with high-resolution graphics”.
Despite the enormous interest generated by the launch of the Spectrum,’ Sinclair still plans to carry on making the ZX-81. But no-one is willing to predict how the advent of the Spectrum will affect future sales of the ZX-81. “This is clearly the big question, of course.
Personally, I feel that the two can co-exist side by side, but obviously there are going to be many people who were going to buy the ZX-81 who are now going to buy the Spectrum instead”.
Certainly Altwasser has faith in the Spectrum. He left Sinclair at the beginning of May this year to set up his own company, in conjunction with Steven Vickers, author of the Spectrum manual. The new company, provisionally called the Rainbow Computing company, will cater for Spectrum users, but Altwasser is distinctly cagey about releasing any details of the company’s plans. However, with Altwasser’s knowledge of the internal workings of the Spectrum and Vickers’s abilities as a software writer, it is a fairly safe bet that they will be producing a range of software and peripherals for the Spectrum.
Altwasser’s abilities as a computer engineer can be judged by an advertisement that appeared in the national press the day after he left Sinclair. “Quite simply we are looking for the world’s best computer designer”. Altwasser is too modest to suggest that Sinclair has already lost the world’s best computer designer, but he will not be easy to replace.