The Path Towards ARM & BBC B - Computerphile

The Evolution of Microprocessors: A Personal Perspective

My involvement with microprocessors began when I was working on an early prototype of the mk14, which used a scmp as its processor. The mk14 had a number of quirks and limitations, but it laid the groundwork for my later work with more advanced processors. One of the challenges we faced was copying the design from a competing project, which proved to be more difficult than anticipated.

To overcome these challenges, I did some debugging on the mk14, which gave me an early hand in understanding how to program microprocessors. However, our efforts were soon surpassed by Roger, who had a different approach to designing microprocessors. He introduced the concept of using a hexadecimal keypad and a seven segment display, this time based on a 6502 processor.

The 6502 was a more powerful and elegant processor than the scmp, with a number of features that made it well-suited for hobbyist projects. It had a simpler circuit design, which was easier to work with, and it was also more powerful than the scmp. The uses for the 6502 were diverse, ranging from simple computations on displays to controlling lab equipment.

The BBC also initiated a backup system using the 6502 processor, which proved popular among hobbyists and university departments. Although I don't have exact sales figures, it's estimated that thousands of units were sold worldwide. The machine was designed to be user-friendly, but it did require some technical knowledge to set up and use.

One of the unique features of the System 1/4, as it came to be known, was its ability to control a 22nd-century interstellar spaceship using an Acorn system one. This feature highlighted the machine's potential for teaching students about microprocessors and programming. The system was marketed as a kit, which limited its appeal to those with some technical knowledge.

In contrast, commercial versions of the System 1/4 were built on larger euro cards and could be expanded to accommodate more peripherals. I never used this version in my day job, but it paved the way for later Acorn systems that became widely popular. My relationship with Acorn was more informal; I would build prototype cards myself and then provide the designs to them, which they would then commercialize.

One of the most significant contributions I made to the development of microprocessors was designing an 80d converter card. This allowed me to develop a similar system at home using a card frame and a 6502 processor. My work on this project gave me valuable experience in programming and using microprocessors in my day job, which prepared me for future challenges.

In my time as a researcher, I encountered the common practice of writing PhD theses by hand on paper and having them typed up by secretaries. However, with the advent of computers, I wanted to write my thesis more efficiently. I designed a text editor for my machine at home, which allowed me to type my thesis directly onto the computer.

The text editor was cobbled together quickly, but it had many limitations, including a change buffer that would crash if used incorrectly. Despite these challenges, I rewrote the program extensively and eventually transformed it into Acorn's Edit program. However, there was much more work involved in developing this program from my original design to the final product.

The 16-bit microprocessors available at the time had limited bandwidth capabilities, which made them inefficient for use with memory cards. This limitation struck us as counterintuitive and motivated our research into more efficient processor designs. The early work on microprocessors laid the groundwork for future innovations in computing, and my personal experience with these machines provided valuable insights that shaped my approach to programming and problem-solving.

"WEBVTTKind: captionsLanguage: enit's up there it's up there yes you might have to get a shot of that it's on the top of the shelf up there left hand side that was your first computer that's the first computer i built yes was that in kit form or did you no no it's entirely home designed including anodizing the aluminium in the kitchen sink and things like that my introduction to computing was through my work in the engineering department at cambridge i was fascinated by airplanes and aerodynamics and i moved from my first degree in maths to a phd in rather theoretical aerodynamics and in the course of that phd i was using some machines to control experiments and such like so i wasn't entirely theoretical but at that time also a bunch of enthusiasts formed the cambridge university processor group i wasn't a founder but i did go to the first meeting and got to know the founders and thought well this this is interesting um i i'm interested in pursuing my my love of flying by building a flight simulator so how do i go about doing that in the late 1970s which is when i started tinkering with computers flight simulators were very large expensive professional machines at the time and so i didn't really have a clear path from starting to build a microprocessor to to building my own flight simulator um that was a big stretch but it was clear that if i if i was going to pursue this that that this was the right place to start and i started at the beginning a microprocessor and some other chips and assembling a very simple computer um and and gradually my i i forgot about the flight simulator bit and got more interested in the computing bit of course the the flight simulator interest came full circle when uh when i discovered aviator on the bbc micro several years later i mean that was a spectacular flight simulator considering the capabilities of the resources it had on the bbc micro so that that kind of completed the circle for me but in the meantime i'd taken the tangent into computing and stayed permanently on it hobbyist computer clubs were definitely becoming popular in the west coast in california and just beginning to start in the uk but we were following behind the americans at that point but it was very much the similar theme probably being a student group it was a similar theme with far smaller resources um but uh yes he was just enthusiasts building stuff comparing notes it was it was really the point in history where it became possible for somebody sitting at home with a little bit of money and a soldering iron to assemble a computer that was pretty basic but still useful and entertaining and the machines i was using in my phd were things like the computer automation lsi4 and they were not enormously more powerful than the sort of things you could build for you know 100 pounds at home people picked up the the techniques for building computers from clubs talking to other people who are ahead of them but also i think pretty much from magazines there were a number of magazines around at the time with titles such as wireless world which is a long-standing one electronics today international i remember was one of my favorites practical electronics maybe that was american i'm not quite sure but these magazines not only had articles on how you could go about building stuff but of course they also had adverts from shops that would sell you stuff i remember being very nervous buying the parts for my first machine i bought the parts mail order from california and that meant using a credit card over the telephone internationally and as a student i'd never done that before well it worked out fine the the chips arrived even they took two or three weeks to write through the post but that's how we found the components the chips were made by the big names of the time texas instruments motorola was around then the microprocessor i used was designed and manufactured by signetics who i think even then were owned by philips we picked up ideas from the meetings of the processor group but then basically we we went off and and bought bits and and tried to assemble them the the processor group also had meetings in each other's houses and i remember a group of people meeting in my house in cambridge which was seven st john's road at the time and uh and somebody called roger wilson that i got to know a little bit through the processor group poking around in my machine and finding a bug in the memory and that was the first time roger found a bug in my hardware it was definitely not the last time at the time we started building machines memory chips were available so they were very small i think my first machine used one kilobit static rams so a thousand bits of memory on a chip but the whole machine was integrated circuits so we were not dealing very much with with transistors at all i i remember i did have to deal with transistors uh because i built um a card for programming eproms and eproms required at that time -5 plus 5 and plus 12 volts and you had to switch a programming pin at quite a high voltage so that particular circuit board has quite a few discrete transistors on but i wasn't an electronics engineer i didn't get on very well with transistors i preferred the the chips even in the analog domain my introduction to electronics was in the analog domain using 741 op amps to build sound systems i built eight-track sound mixers and so on i could understand chips i i did a lot of my own soldering yes and and the computer stuff was all built with vera wire which was a fairly standard technology at the time it involved sold rig but you had a wiring pen and a standard printed circuit board that was a generic and you put the sockets in and then with this wiring pin you would basically wrap it around one of the socket legs take it around a few combs and then wrap it around the other end this was very fine wire with i think of some kind of polyurethane insulation i think and when you soldered it the insulation melted but where the wire was not soldered it was insulated so you could run lots of wires down these combs and they wouldn't short circuit and i learned sometime later that the the fumes given off by soldering this wire were not very pleasant but you didn't learn at the time this was not advertised at the time no i'm sure what i recall and this is a long time ago and i'm not known for my memory um if you talk to to sophie wilson her memory of this era is much better than mine but i seem to recall i was in my office at the engineering department and and the phone rang um there was no email then um and it was herman and and uh herman said he'd like to come and talk to me um and i think he came to my office in the engineering department sat down there and said that he and chris curry were thinking of starting a company and they were looking for a few people to help them on the technical side they obviously looked at the processor group because that was the area they were looking at was i interested and i'm fairly sure my reply was along the lines of well this is a fairly recently acquired hobby as far as i'm concerned i can't claim any expertise but you know if you think i can help then then then i'm happy to have a go um and that is where it started the next meeting i remember was a meeting with herman chris and chris turner at the forzon george on midsummer common in cambridge and we sat in this pub the four of us and the plans were firming up a bit i don't remember if at that time they'd begun to talk about the fruit machine contract which was the first piece of development contractual work they got the fruit machine contract was about converting fruit machines from electromechanical which is how they all worked up to that point to microprocessor controlled which was the way it was all going and has stayed ever since so we were taking a fruit machine which is a one-armed bandit a thing you never put money into but i'm very averse to all forms of gambling and i understand why the state has to license and tax it i still don't understand why they sponsor it through national lotteries i think this is a very bad idea but that's just my principles which slightly clash with working on the fruit machine project i wasn't entirely comfortable but um it was a technical challenge and that seemed to override my principles at the time um yes so we basically took the old electromechanical controller out and then replaced it with a formidably complicated microprocessor control system which involved two national semiconductor scmp microprocessors running in parallel getting that to work and passing some of the robustness tests was quite instructive so as soon as we said we had a working system the first thing they wanted us to do was plug it into a main socket with one of those block adapters plug a small arc welding kit into the other socket and then weld metal while using the fruit machine to see how this this was what passed as emc testing in those days i think and the other problem they knew about was that there were some electronic fruit machines already out on the market and users had discovered that they were very prone to paying out if you used an electronic cigarette lighter close to the cash socket the electronic cigarette lighters were just a great source of interference it just injects a jolt and if you did this enough times it would throw cash at you so one thing that that roger did very early on was built an fm radio receiver which detected anybody trying to do this and immediately made sure whatever the machine did it didn't pay out basically it shut down and and reset and started again it's any sign of this i was mostly involved in developing the software for this parallel system um chris turner did most of the hardware as i recall and and roger developed this fm detector for electronic cigarette lighters um i should say that i was my day job was still in the university i was a phd student and then research fellow through till 1981 i only joined the staff in october 81. so i don't really know what happened to the to the fruit machine business once we um got something working um i i i don't know if it led to a longer contract what i do recall is that uh concurrent with that chris was setting up science of cambridge with clive sinclair and they decided to try and sell this mk14 a sort of small microprocessor pcb with a hexadecimal keypad and seven segment display and i know they got the first circuit for this and i veriwired a prototype of that in my front room um discovered that in copying the mass programmed rom into the two fusible link roms that were on the mk14 they managed to copy it wrong so i did a little bit of debugging of that so i had an early hand in the mk 14 work but roger looked at the mk14 and and did the classic thing of saying uh i can do better than that um and and he went home at easter came back after easter with a design for a machine with again a hexadecimal keypad and a seven segment display this time based on a 6502 the mk14 used the scmp that we'd used in the fruit machine the 6502 is a nicer processor to program the scmp had a number of curious features um and and this the circuit was simpler it was generally more elegant and more powerful the uses you could put this to were pretty basic i mean you could in the lab use it to control um you could write software that would wiggle the i o pins to control something um you could write little programs to um do simple computations on the display and so on if you believe the bbc initiate the backup system i'm very sorry about this but that was the backup system with blake 7 you can control the 22nd century interstellar spaceship with a acorn system one so it was really an instrument for learning about microprocessors it found quite a lot of interest in hobbyists and i think some university departments also used it for teaching students the sales i don't know the sales numbers but i'm guessing that that they were in the thousands maybe 10 20 000 i'm not sure they required people who were prepared to do quite a lot of work to get into them and to use them to do things and i think we even they were they were sold as kits so um they were restricted to the market of people who knew which end to pick up a soldering iron did they ever cross into your day job did you would you ever take one into the lab because obviously you've mentioned that you were working on things like aerodynamics and what have you were the things you could potentially use it for in your day job or did you keep did your two wheels were they separate i never used a system one in my day job um but the the system one was built on two euro cards and very soon after that was released um cpu limited under the marketing name acorn built larger systems which were based on card frames and these cards were plugged into a rack and then you could put a video card in there you could put an interface to a conventional keyboard you could basically grow it up to something bigger now i didn't use that directly my relationship with with the embryonic acorn was that i was building little cards myself prototyping them and then giving the design to acorn who then commercialized them in particular i designed an 80d converter so i had a very similar system at home based in a card frame which i built myself and i did use that in my work up to those days most people who wrote a phd thesis would write it by hand on paper and give it to a secretary to type up who would laboriously type it onto sheets of paper but computers were just arriving so i wanted to write my phd thesis i got to that point so the first thing i did was i wrote a text editor for my machine at home which i'd built myself and then i wrote my thesis on that and then i devised a way of of conveying it across through a parallel cable to one of these computer automation lsi4s and then we could take the information to an lsi4 with a daisy wheel printer attached and because my thesis has some mathematics in it i needed a big twin wheel daisy wheel it had a roman wheel and a greek wheel and my thesis was printed on about 200 feet of continuous paper so it came out like a very large toilet roll and then you had to snip it up and then had to guillotine it up into relevant size units and and bind it yes i also used um the machine i built at home in i think for gathering some experimental data but it's the first use was for writing the thesis my text editor which was cobbled together very quickly and was full of death traps so it had a it had a change buffer and if you overran the change buffer by one character it just crashed and lost lost everything that was tidied up a bit by which i mean extensively rewritten and became acorn's edit program but as i say there was far more work that went into transforming what i had written into the product that i'd put into the first prototype the 16-bit microprocessors could not use the bandwidth that was available in the memory that people put in these machines so you spent your money you bought some bandwidth and then you were coupling this to a processor that couldn't use that basic resource and this just struck us as wrongit's up there it's up there yes you might have to get a shot of that it's on the top of the shelf up there left hand side that was your first computer that's the first computer i built yes was that in kit form or did you no no it's entirely home designed including anodizing the aluminium in the kitchen sink and things like that my introduction to computing was through my work in the engineering department at cambridge i was fascinated by airplanes and aerodynamics and i moved from my first degree in maths to a phd in rather theoretical aerodynamics and in the course of that phd i was using some machines to control experiments and such like so i wasn't entirely theoretical but at that time also a bunch of enthusiasts formed the cambridge university processor group i wasn't a founder but i did go to the first meeting and got to know the founders and thought well this this is interesting um i i'm interested in pursuing my my love of flying by building a flight simulator so how do i go about doing that in the late 1970s which is when i started tinkering with computers flight simulators were very large expensive professional machines at the time and so i didn't really have a clear path from starting to build a microprocessor to to building my own flight simulator um that was a big stretch but it was clear that if i if i was going to pursue this that that this was the right place to start and i started at the beginning a microprocessor and some other chips and assembling a very simple computer um and and gradually my i i forgot about the flight simulator bit and got more interested in the computing bit of course the the flight simulator interest came full circle when uh when i discovered aviator on the bbc micro several years later i mean that was a spectacular flight simulator considering the capabilities of the resources it had on the bbc micro so that that kind of completed the circle for me but in the meantime i'd taken the tangent into computing and stayed permanently on it hobbyist computer clubs were definitely becoming popular in the west coast in california and just beginning to start in the uk but we were following behind the americans at that point but it was very much the similar theme probably being a student group it was a similar theme with far smaller resources um but uh yes he was just enthusiasts building stuff comparing notes it was it was really the point in history where it became possible for somebody sitting at home with a little bit of money and a soldering iron to assemble a computer that was pretty basic but still useful and entertaining and the machines i was using in my phd were things like the computer automation lsi4 and they were not enormously more powerful than the sort of things you could build for you know 100 pounds at home people picked up the the techniques for building computers from clubs talking to other people who are ahead of them but also i think pretty much from magazines there were a number of magazines around at the time with titles such as wireless world which is a long-standing one electronics today international i remember was one of my favorites practical electronics maybe that was american i'm not quite sure but these magazines not only had articles on how you could go about building stuff but of course they also had adverts from shops that would sell you stuff i remember being very nervous buying the parts for my first machine i bought the parts mail order from california and that meant using a credit card over the telephone internationally and as a student i'd never done that before well it worked out fine the the chips arrived even they took two or three weeks to write through the post but that's how we found the components the chips were made by the big names of the time texas instruments motorola was around then the microprocessor i used was designed and manufactured by signetics who i think even then were owned by philips we picked up ideas from the meetings of the processor group but then basically we we went off and and bought bits and and tried to assemble them the the processor group also had meetings in each other's houses and i remember a group of people meeting in my house in cambridge which was seven st john's road at the time and uh and somebody called roger wilson that i got to know a little bit through the processor group poking around in my machine and finding a bug in the memory and that was the first time roger found a bug in my hardware it was definitely not the last time at the time we started building machines memory chips were available so they were very small i think my first machine used one kilobit static rams so a thousand bits of memory on a chip but the whole machine was integrated circuits so we were not dealing very much with with transistors at all i i remember i did have to deal with transistors uh because i built um a card for programming eproms and eproms required at that time -5 plus 5 and plus 12 volts and you had to switch a programming pin at quite a high voltage so that particular circuit board has quite a few discrete transistors on but i wasn't an electronics engineer i didn't get on very well with transistors i preferred the the chips even in the analog domain my introduction to electronics was in the analog domain using 741 op amps to build sound systems i built eight-track sound mixers and so on i could understand chips i i did a lot of my own soldering yes and and the computer stuff was all built with vera wire which was a fairly standard technology at the time it involved sold rig but you had a wiring pen and a standard printed circuit board that was a generic and you put the sockets in and then with this wiring pin you would basically wrap it around one of the socket legs take it around a few combs and then wrap it around the other end this was very fine wire with i think of some kind of polyurethane insulation i think and when you soldered it the insulation melted but where the wire was not soldered it was insulated so you could run lots of wires down these combs and they wouldn't short circuit and i learned sometime later that the the fumes given off by soldering this wire were not very pleasant but you didn't learn at the time this was not advertised at the time no i'm sure what i recall and this is a long time ago and i'm not known for my memory um if you talk to to sophie wilson her memory of this era is much better than mine but i seem to recall i was in my office at the engineering department and and the phone rang um there was no email then um and it was herman and and uh herman said he'd like to come and talk to me um and i think he came to my office in the engineering department sat down there and said that he and chris curry were thinking of starting a company and they were looking for a few people to help them on the technical side they obviously looked at the processor group because that was the area they were looking at was i interested and i'm fairly sure my reply was along the lines of well this is a fairly recently acquired hobby as far as i'm concerned i can't claim any expertise but you know if you think i can help then then then i'm happy to have a go um and that is where it started the next meeting i remember was a meeting with herman chris and chris turner at the forzon george on midsummer common in cambridge and we sat in this pub the four of us and the plans were firming up a bit i don't remember if at that time they'd begun to talk about the fruit machine contract which was the first piece of development contractual work they got the fruit machine contract was about converting fruit machines from electromechanical which is how they all worked up to that point to microprocessor controlled which was the way it was all going and has stayed ever since so we were taking a fruit machine which is a one-armed bandit a thing you never put money into but i'm very averse to all forms of gambling and i understand why the state has to license and tax it i still don't understand why they sponsor it through national lotteries i think this is a very bad idea but that's just my principles which slightly clash with working on the fruit machine project i wasn't entirely comfortable but um it was a technical challenge and that seemed to override my principles at the time um yes so we basically took the old electromechanical controller out and then replaced it with a formidably complicated microprocessor control system which involved two national semiconductor scmp microprocessors running in parallel getting that to work and passing some of the robustness tests was quite instructive so as soon as we said we had a working system the first thing they wanted us to do was plug it into a main socket with one of those block adapters plug a small arc welding kit into the other socket and then weld metal while using the fruit machine to see how this this was what passed as emc testing in those days i think and the other problem they knew about was that there were some electronic fruit machines already out on the market and users had discovered that they were very prone to paying out if you used an electronic cigarette lighter close to the cash socket the electronic cigarette lighters were just a great source of interference it just injects a jolt and if you did this enough times it would throw cash at you so one thing that that roger did very early on was built an fm radio receiver which detected anybody trying to do this and immediately made sure whatever the machine did it didn't pay out basically it shut down and and reset and started again it's any sign of this i was mostly involved in developing the software for this parallel system um chris turner did most of the hardware as i recall and and roger developed this fm detector for electronic cigarette lighters um i should say that i was my day job was still in the university i was a phd student and then research fellow through till 1981 i only joined the staff in october 81. so i don't really know what happened to the to the fruit machine business once we um got something working um i i i don't know if it led to a longer contract what i do recall is that uh concurrent with that chris was setting up science of cambridge with clive sinclair and they decided to try and sell this mk14 a sort of small microprocessor pcb with a hexadecimal keypad and seven segment display and i know they got the first circuit for this and i veriwired a prototype of that in my front room um discovered that in copying the mass programmed rom into the two fusible link roms that were on the mk14 they managed to copy it wrong so i did a little bit of debugging of that so i had an early hand in the mk 14 work but roger looked at the mk14 and and did the classic thing of saying uh i can do better than that um and and he went home at easter came back after easter with a design for a machine with again a hexadecimal keypad and a seven segment display this time based on a 6502 the mk14 used the scmp that we'd used in the fruit machine the 6502 is a nicer processor to program the scmp had a number of curious features um and and this the circuit was simpler it was generally more elegant and more powerful the uses you could put this to were pretty basic i mean you could in the lab use it to control um you could write software that would wiggle the i o pins to control something um you could write little programs to um do simple computations on the display and so on if you believe the bbc initiate the backup system i'm very sorry about this but that was the backup system with blake 7 you can control the 22nd century interstellar spaceship with a acorn system one so it was really an instrument for learning about microprocessors it found quite a lot of interest in hobbyists and i think some university departments also used it for teaching students the sales i don't know the sales numbers but i'm guessing that that they were in the thousands maybe 10 20 000 i'm not sure they required people who were prepared to do quite a lot of work to get into them and to use them to do things and i think we even they were they were sold as kits so um they were restricted to the market of people who knew which end to pick up a soldering iron did they ever cross into your day job did you would you ever take one into the lab because obviously you've mentioned that you were working on things like aerodynamics and what have you were the things you could potentially use it for in your day job or did you keep did your two wheels were they separate i never used a system one in my day job um but the the system one was built on two euro cards and very soon after that was released um cpu limited under the marketing name acorn built larger systems which were based on card frames and these cards were plugged into a rack and then you could put a video card in there you could put an interface to a conventional keyboard you could basically grow it up to something bigger now i didn't use that directly my relationship with with the embryonic acorn was that i was building little cards myself prototyping them and then giving the design to acorn who then commercialized them in particular i designed an 80d converter so i had a very similar system at home based in a card frame which i built myself and i did use that in my work up to those days most people who wrote a phd thesis would write it by hand on paper and give it to a secretary to type up who would laboriously type it onto sheets of paper but computers were just arriving so i wanted to write my phd thesis i got to that point so the first thing i did was i wrote a text editor for my machine at home which i'd built myself and then i wrote my thesis on that and then i devised a way of of conveying it across through a parallel cable to one of these computer automation lsi4s and then we could take the information to an lsi4 with a daisy wheel printer attached and because my thesis has some mathematics in it i needed a big twin wheel daisy wheel it had a roman wheel and a greek wheel and my thesis was printed on about 200 feet of continuous paper so it came out like a very large toilet roll and then you had to snip it up and then had to guillotine it up into relevant size units and and bind it yes i also used um the machine i built at home in i think for gathering some experimental data but it's the first use was for writing the thesis my text editor which was cobbled together very quickly and was full of death traps so it had a it had a change buffer and if you overran the change buffer by one character it just crashed and lost lost everything that was tidied up a bit by which i mean extensively rewritten and became acorn's edit program but as i say there was far more work that went into transforming what i had written into the product that i'd put into the first prototype the 16-bit microprocessors could not use the bandwidth that was available in the memory that people put in these machines so you spent your money you bought some bandwidth and then you were coupling this to a processor that couldn't use that basic resource and this just struck us as wrong\n"