viewpoints

Vdoi:10.1145/1941487.1941501 Jason Fitzpatrick Interview An Interview with Steve Furber, designer of the seminal BBC System and the widely used ARM , reflects on his career.

tephen Byram Furber is the a founder. I went along to the very first ICL Professor of Com- meetings and started building com- puter Engineering in the The BBC Micro was puters for fun, which was fairly scary School of Computer Sci- just the front end in those days because the components ence at the University of of something that had to be ordered from California by SManchester, U.K. Furber is renowned mail order using a credit card. I was a for his work at Ltd., was designed as student so credit cards were fairly scary where he was a principal designer of then; using them internationally was the BBC Microcomputer System and a dual processor even scarier. But we got the micropro- the ARM microprocessor, both of from the outset. cessors. My first machine was based which have achieved unique historical on the 2650, which not many significance. people have heard of these days. It The BBC Micro platform was funda- had a full kilobyte of static RAM main mental to in British educa- memory. I assembled the circuit board tion in the 1980s and directly led to the using Verowire, which is a little wiring development of the ARM architecture. of the information age (see http://www. pen where you hand-wired the things The ARM architecture is the most wide- computinghistory.org.uk/.) A video of together; you soldered it, which melted ly used 32-bit RISC architecture and the the interview is available at http://www. the insulation and made the connec- ARM processor’s power efficiency—per- computinghistory.org.uk/det/5438/ tions. I understand it gave off carcino- forming the same amount of work as Steve-Furber-Interview-17-08-2009/; a genic vapor, but it hasn’t got me yet. other 32-bit processors while consum- condensed version of the interview is That’s how I built these things. I ing one-tenth the amount of electric- presented here. built myself a small rack—I couldn’t ity—has resulted in the widespread afford a commercial rack, so I made dominant use of the ARM processor in I’d like to talk to you about your in- one and got the 2650 system going. mobile devices and embedded systems. volvement with Acorn, and what it’s In the Processor Group, enthusiasts Furber is a of the Royal Acad- led to today. exchanged notes with each other. I re- emy of Engineering, of the Royal So- I was at the University [in Cam- member coming to my ciety, the IEEE, the British Computer bridge]; I read maths as an under- house for one meeting of the Proces- Society and the Institution of Engi- graduate and I went on to do a Ph.D. sor Group, looking at my machine and neering and Technology (IET), and was in aerodynamics. During my Ph.D. I poking away at it—finding faults in appointed Commander of the Order of got interested in aspects of flight, and the memory and stuff like that. Then the British Empire (CBE) in 2008. then I heard about the formation of while I was still a Ph.D. student in the Jason Fitzpatrick, a computer his- the University Processor Engineering Department, Hermann torian and the curator at the Centre Group. I thought maybe I should join Hauser came knocking on my door and for Computing History at Suffolk, up with these guys and see if I could explained that he and Chris Curry were U.K., conducted an extensive interview build myself a flight simulator or some- thinking of starting a consultancy com- with Furber on behalf of the museum, thing like that. I was involved in the pany in the microprocessor business. which is dedicated to creating a perma- University Processor Group from its They had been looking to the Univer- nent public exhibition telling the story foundation although I wasn’t actually sity Processor Group as the source of

34 communications of the acm | may 2011 | vol. 54 | no. 5 viewpoints

technical people who might be able to you interfered with it, it should defi- think the Altair had probably appeared help them; he asked me if I was inter- nitely not pay out. The things were about this time in the States. ested. I said, “Well, I’m just a hobbyist. tested by plugging a mains adapter In the University Processor Group, I’ve been doing this for fun. But if you into the wall, plugging the fruit ma- the real men built computers with TTL. think I can help, I’m willing to give it a chine into one socket, and an weld- It was only the wimps like me that used go.” That’s how I joined the embryonic ing transformer into the other. Some- newfangled , which Acorn, before it was Acorn. body welded metal together while you were kind of cheating because you got operated the fruit machine to see if the too much functionality in one package. V Was it based inside Sinclair’s building thing was robust to sparking. But yes, microprocessors were just en- at the time? tering the public consciousness, so the Yes, the first things we did were in Fantastic! The feeling at that time was MK14 from Science of Cambridge was the Science of Cambridge Building in very much of the hobbyist. You just en- an example of a microprocessor on a King’s Parade. Chris Curry was set up joyed doing that kind of thing, and the with a hexadeci- running Science of Cambridge with whole industry has pretty much come mal keypad and seven segment display; Clive. Hermann and Chris did bits of out of that. Is that fair to say? you could put assembly code into it and Acorn work in there. In fact the first Yes, that’s right. We are talking about make it run. Sophie saw the MK14 and thing I did for Acorn was actually not for the late 1970s before the IBM PC started, said something which she said many Acorn, it was for Science of Cambridge. before the Apple II had appeared. There times—basically, “I could do better I hand-built the prototype MK14; I got were some very box machines. I than that.”— and she went home over a circuit diagram and built one using Verowire, soldering in my front room. The MK14 was basically a copy of the SC/MP devel- opment kit. They had taken what was a masked program ROM from the de- velopment kit and copied it into two fusible link PROMS for the MK14, and they managed to copy it wrong. So I de- bugged this thing in my front room. That was the first piece of work I did for them. Then Chris and Hermann got a con- tract to do some development work on microprocessor controlled fruit machines, which were very new at that time. Up to that date fruit machines had all been controlled by relays and so on; this was an early attempt to do micro- processor stuff. We used two SC/MPs in a rack to control the fruit machine. In fact, the software for that was boot- strapped from the 2650 machine I built in the Processor Group; it was used as a dumb terminal into the SC/MP devel- opment kit, and we brought this fruit machine controller up. The main chal- lenge in those days was to make these things robust. Very early on people had discovered if you just sparked electron- ic cigarette lighters next to the fruit ma- chine, they would often pay out.

Yes, the program counter jumps off er b

ur somewhere and anything can happen! f e v

e Yes. So that was when Sophie Wil- st

f son came in. She designed an FM re- y o s

e ceiver front end that would trigger t

our whenever you flicked one of these ciga- c

ph rette lighters and cause the SC/MPS to ra g

o reset; it would definitely not pay out. t o h

P [laughs] That was the requirement—if

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Easter holiday and came back with a neither Z80 nor CP/M, although a couldn’t let them in. Nobody was ex- design she called the Hawk, which was little bit later you could buy a Z80 sec- pecting this, either. 6502-based. Hermann looked at this ond processor to run CP/M; we kind of The machine was first sold in Jan- and thought he could sell it; that be- met the spec in the end. But no, they uary of 1982, so this may have been came the . The name were sufficiently convinced by what later in 1982. Acorn was introduced originally just we could do with the 6502 that they as a trading name. The company was moved the spec to the machine that And that was the first time you thought called Cambridge Processor Unit Ltd. Acorn had already begun to get on the this is big? drawing board. The Proton was always Well, this is when you first felt the If you look at those machines today, designed as a dual processor. The fact scale of public interest. People were the System 1 and the MK14, they are the BBC Micro had a second proces- prepared to hire a coach from Birming- what most people would describe now sor connection was actually because ham to hear this bunch of techies, who as unusable. But these things sold in a the BBC Micro was just the front end probably didn’t know how to speak in big way. of something that was designed as a public, say something about this hob- The System 1 and the MK 14 sold dual processor from the outset. byist computer thing. Of course, we faster than people could put the kits to- I remember that when the BBC always had the education market in gether. I think the System 1 was mainly was talking to Acorn—I wasn’t in- mind, but this was much bigger than sold as a kit, so you got the parts and volved in the commercial discus- just the education market in terms of you had to solder it together. But there sions, I was just a techie—they were interest. We actually went on tour with was lots of interest. It was really the confident this machine would sell, this seminar. We gave it twice more only way the general public could get and on the back of their programs at the IET to soak up demand. We did their hands on anything that looked we’d sell 12,000 of these machines. a tour of the U.K. and Ireland. Every- like a computer at that time. Real com- That was big numbers to Acorn. Not where we went there was a big turnout. puters cost a million pounds, lived in huge numbers—we’d probably sold There was real, real interest. clean rooms, and were only touched several thousand Atoms—but it was by men in white coats; whereas these really worth going for. Nobody imag- What sort of people were coming to things you could buy for £100 or £200 ined that that estimate would be off this? and play with at home. by a factor of a hundred—one and A wide range of people. I think it is the a half million were shipped in the same phenomenon as with the System 1 It was just the want to own and control end—because nobody really antici- but on a bigger scale. It was a bunch of one of these things. A lot of it was driv- pated the wave of interest. people who recognized that computers en by science fiction… I really realized that this was a phe- were about to come within their reach, Of course, the real science-fiction nomenon when Sophie, Chris Turn- when they’d been behind closed doors aspect is they got used as props in TV er, and I agreed to do a seminar at the throughout past history. There were shows as well. So the Acorn System IET in Savoy Place in London. It has lots of companies building machines 1 was featured as the computer on a big central amphitheatre that sits at the time. We’ve mentioned Sinclair, “Blake’s 7.” There was quite a lot of about 500 or 600 people. They asked but if you go and look at the machines competition between Acorn and Sin- us to do a seminar on the BBC Micro. coming out, the 1980s was a real era of clair at the time. had We went down there thinking this is diversity. Wonderful quirky machines of proudly boasted that you could control a big room, I wonder if they’ll fill it? all shapes and flavors, all coming out of a nuclear power station with his ZX81. Three times the number of people companies a bit like Acorn: small start- Well, this was nothing compared with they could get in the room turned ups; enthusiasts the public couldn’t controlling a 21st century interstellar up. People booked coaches from Bir- perhaps fully trust. Unless you were a cargo ship [on the “Blake’s 7” televi- mingham; they had to be sent home hobbyist and a real enthusiast yourself, sion program] with an Acorn System 1. because Health and Safety said they you didn’t know who to trust. Then the BBC put their name on You win, hands down. this machine from Acorn. I think that That’s right! [laughs] We always had the really was the key to the success of the BBC Micro, even though by the Going forward to the BBC Micro, obvi- education market in standards of the competition it was ously the BBC came to Acorn with the mind, but this was a slightly expensive machine. It was specification for a machine? How did slightly higher spec and that was part- that change things at Acorn? The Atom much bigger than just ly the BBC’s requirements. The BBC was out and it was selling well. Then all the education market imposed—no, imposed is the wrong of a sudden you were shot into fame in word—encouraged us to go with a par- the computing industry. in terms of interest. ticular spec. The spec was all negoti- The BBC Micro was a huge phe- ated and agreed; there was no imposi- nomenon. Of course, when the BBC tion. But they were tough negotiations. came their spec was a Z80 machine The BBC had a pretty clear idea of what running CP/M. The BBC Micro was they wanted. The fact that we pushed

36 communications of the acm | may 2011 | vol. 54 | no. 5 viewpoints the technology a bit—you know, we ran them at that price. So it went up to the memory a bit faster, we made an £299, £399. We were trying hard to keep early use of semi-custom chips, we had The BBC imposed­— the price down. But really, how could these two ULAs that gave us quite a lot no, imposed is you make the machine cheaper? If you of excitement—all pushed the price of look at a Spectrum, then of course ev- the machine up a bit. It was an expen- the wrong word— erything about it is cheaper, including sive machine, but despite that, a much encouraged us the keyboard. The BBC had by today’s broader market was comfortable with standards a stunningly high-quality it because it had the BBC name. to go with a keyboard. Today’s keyboards are very The machine itself was low level. If particular spec. cheap elastomeric. Every switch on the you connected something to the back, BBC Micro keyboard had a pair of gold like a joy stick, it was easy to communi- wires that touched when they crossed. cate with it because you weren’t, as you When you pushed the key down they would be with today’s PC, so high up in sprang together and touched, so you the software stack. The BBC Micro was using technology. In weren’t making the contact with the key easy and anybody could read the user fact, you could probably make a BBC press; you were removing the obstruc- guide; if they had a little bit of technical Micro in a single chip and sell it very tion that was preventing the contact. know-how they could build their own cheaply. I can still run BBC Micro And BBC keyboards were formidably electronics to go into the one mega- programs on my laptop. In fact I have robust. There were some manufactur- hertz and program it. It was easy. BBC BASIC for Windows, which is a ing problems with them. There was a I’m quite sad we’ve lost some of that. I very faithful emulation. It’s produced batch that were manufactured with the think it’s much tougher now for teenag- by Richard Russell, who is one of the key switches about half a millimeter off ers with technical interest to say, “I want people who worked for the BBC when the PCB; when you hammered on them to build one of these things, plug it into we were negotiating with them in the the force got transmitted through to the my computer and make it do stuff.” 1980s. I have an Archimedes solder joints on the back then the PCB that I run on the PC, and I have a BBC tracks broke. But when they were made Yes, I had a BBC Micro and connected emulator that I run on the Archimedes properly, they would last 10 years of kids up various different bits of equipment emulator that runs on the PC. thrashing them. The machine took a to it and had to program this thing hammering. You know, mine still works. down to the metal, talking directly to the Emulating emulation! chips; you’re talking to the very pins that And it’s still faster than the original They’re fantastic machines. So what you just wired up something to. Like you BBC Micro because that’s how much did the success of the BBC Micro do to say, that’s completely gone. You have to compute power we’ve got now. So you Acorn? go through layers and talk through Win- can still run the stuff, but you can’t in- Acorn grew rapidly. When the BBC dows, etc. How does one get into hard- terface hardware to it so easily. contract was signed, I was still a re- ware programming now? We’re running There’s an interest in actually build- search fellow at the University; my day so fast that you can’t even make circuit ing something much more basic again job was doing aerodynamics. I guess boards to connect to it because the fre- around today’s microcontroller tech- Acorn at that stage employed maybe 30 quency just won’t have it. nology. My guess the market for that is people. I joined them full time in Oc- You’re right; the problem isn’t sim- small but not insignificant. tober 1981, and by 1983 the company ply the stacks of software. The prob- I think the nearest thing you get at had grown to 400 people, just to man- lem is the hardware now...the signal- the moment is a PIC development kit age this stuff. There was no real sales level hardware is very difficult to work for about £20; with a PC you can write activity involved because the stuff sold with and requires a lot of skill and PIC Assembly code, load it into the faster than you could make it—it just knowledge. But of course, you could PIC, and do all sorts of stuff with it. I do walked off the shelves. So it was really still build a slow interface. If you want know quite a few people who use PICs building the technical team up; and an interface at a megahertz, then con- this way. That’s probably the nearest we had a strong manufacturing team. necting to a megahertz is no harder you get. But with a PIC, in some sense If you’re going to make millions, you now than it was in 1980. Actually, a you’re going to a lower-level interface want to know something about pro- megahertz means you can do a mil- than on a BBC Micro. curement. Acorn didn’t actually man- lion things a second, which is quite a ufacture; it was all sub-contracted. We lot for many purposes. So how would To go back to the point about the price had to build skills in manufacturing. people access that? I guess they get of the BBC, it was expensive. You had The BBC contract also required lots some of it through the Lego robotic Spectrums, which were under half the of exotic technology beyond the basic systems and so on. But in a sense, a price. Was a big part of the negotia- machine. The re- bit too much of that is prefabricated. tions trying to keep the price down? ceiver was a bit of unknown technolo- It’s a bit too ready-to-go. But you are Yes. You may remember that we gy we had to make; the second proces- talking at quite a low level to the mi- launched (I may get the numbers wrong sors including the Z80 running CPM. crocontroller. There’s no reason now here) the Model A at £239 and the B There were a lot of things to go around why we can’t make BBC- like products at £339, but really we couldn’t make it, so we grew technical teams.

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We also realized the price point very involved in this. We were already was quite good for schools and pro- thinking the BBC Micro has been a big fessional users, but it was too high success; we need to build on this. We for hobbyist and most home users, could put second processors on, which so we developed the Electron, which tided us over for a bit. But really we was a cost-reduced BBC Micro - not needed to be thinking about the next an entirely happy story. There wasn’t big machine. It was clear that we were ACM much wrong with the machine, but going to step up from 8 bits. 16-bit pro- for Christmas 1983 when there would cessors were already around and going Journal on have been a huge market we couldn’t into some competing products. get the electronics reliable enough. We looked at the 16-bit processors Computing and By 1984 when we cracked it and could that were around and we didn’t like make lots of them, the market had them. We built test bench prototype Cultural gone. We ended up with a quarter of a machines with these. We didn’t like million of them in the warehouse that them for two reasons. Firstly, they were Heritage were eventually sold below cost. all going to 16 bits by adopting mini- But yes, the company went from a computer-style instruction sets, which small, experimental start-up to big, es- meant they had some very complex tablished...well, is 400 big—medium- instructions. The anecdote I always re- sized maybe? member is that the National Semicon- ductor 32016 had a memory-to-memo- What was the atmosphere like with ry divide instruction that took 360 clock the people that worked there? Or was cycles to complete; it was running at 6 the excitement lost in the numbers of megahertz, so 360 clock cycles was 60 people? microseconds; it was not interruptible No, there was a core group who did while the instruction was executing. the really ambitious technical stuff. Single density floppies, if you handled We did begin to get the idea that we them chiefly with interrupts, give an in- could take on anything. We knew terrupt every 64 microseconds, double there was competition. We were a bit density every 32. Hence you couldn’t over- focused on Sinclair as the com- handle double density floppy disks. ◆ ◆ ◆ ◆ ◆ petition. Standard problem: seeing The complex instruction sets gave the parochial competition and miss- them very poor real-time response. JOCCH publishes papers of ing the real competition from much The second problem we had was significant and lasting value in further away. Technically we felt very that none of them kept up with mem- all areas relating to the use of ICT much on top of what we were trying to ory. Commodity memory at the time do, and we kept taking on bigger and was, as it still is today, DRAM—it was in support of Cultural Heritage, bigger challenges. We felt we’d devel- rather smaller DRAM chips—and this seeking to combine the best of oped the Midas touch when it came DRAM had a certain bandwidth. If you computing science with real to advanced technology; that’s a lot of ran the DRAM at full spec, you get a attention to any aspect of the the background to the development certain bandwidth. We deduced from a of the ARM microprocessor. This was number of experiments that compute cultural heritage sector. a very short period of time when you power goes with memory bandwidth. look back. The first sale of the BBC Mi- But these microprocessors wouldn’t ◆ ◆ ◆ ◆ ◆ cro was January 1982. The ARM design even use the bandwidth that was there; started in October 1983 and the first they couldn’t keep up with the memo- ARM chips were in our hands in April ry. This struck us as the wrong answer. 1985. It was only four years from be- So we were feeling unsatisfied with www.acm.org/jocch ginning to sell BBC Micros to having the microprocessors we could go out www.acm.org/subscribe ARM chips in our hands. and buy when I’m pretty sure it was Hermann who dropped a couple of Going on to the ARM chip, how did that papers on our desks, which were early come about? What started you guys RISC papers from Berkeley and Stan- working on a new type of processor? ford, where a grad class had designed The advanced R&D group, which I a microprocessor that was competitive was in with Sophie and several other with the best industry could offer. We folk, was responsible for looking fur- looked at this, and thought how would thest out in terms of what the company we really like a microprocessor to look? was going to do for product. Hermann Sophie began tinkering with instruc- was very hands-on—he was always tion set architecture, inspired consid-

38 communications of the acm | may 2011 | vol. 54 | no. 5 viewpoints erably by the Berkeley and Stanford try as it catches up. But if we set about they didn’t know what to do with it. RISC work, but also by what she under- doing this, we’ll learn something, we’ll stood of the 6502, and also what was understand something about what it So we’re talking about a chip now that needed to write a good BASIC inter- takes to build a good microprocessor; is in something like 92% of mobile de- preter. Sophie had written several BA- and then we’ll be better at recognizing vices today? SIC interpreters by then for the Atom, a good one when we see it. We didn’t Yes. Around the end of 2007, the for the BBC Micro, for the 32016 sec- expect this to go through. To us, build- ten-thousand-millionth ARM had been ond processor, and so on. She sketched ing microprocessors was a black art. shipped, so there are more ARMs than out an instruction set. The big companies had hundreds of people on the planet. I believe produc- Then in October 1983 Sophie and I people, and it took them 10 revs of the tion is currently running at about 10 went to visit the chip before it started to work sensibly. It million a day. It is projected to rise to in Phoenix, Arizona. They were design- just looked like a black hole, and Acorn about one per person on the planet per ing a slightly extended 6502, the 24-bit couldn’t afford that size of black hole. year within two or three years. address 6502 that became the 65C816. But we got on with it. It turned out We went in expecting to find big, shiny there is no magic. Microprocessors They’re mind-blowing numbers. American office buildings with lots of are just a lump of logic, like everything Look­ing at all this and seeing how it’s glass windows and fancy coffee ma- else we’d designed, and there are no changed us as people -to have this com- chines. What we found was a bungalow formidable hurdles. The RISC idea puting power in our pockets has com- in the suburbs of Phoenix. They hired was a good one; it made things much pletely changed the way we are and the school kids during the summer vaca- simpler. Eighteen months later, af- way we live our lives. And you played an tion to do some of the basic cell design. ter about 10 or 12 man-years of work, absolute key part in that. So what does Yes, they’d got some big equipment, we had a working ARM in our hands, it feel like, to know that you played a but they were basically doing this on which probably surprised us as much big part in it? Apple IIs. My strong memory is walk- as it surprised everybody else. It’s kind of magic, isn’t it? I mean ing out of there saying to each other, In July 1985, we’d had the proces- it’s largely serendipity. I spent some “Well, if they can design a micropro- sor on our bench running for a couple of my last two years at Acorn trying to cessor, so can we.” of months; we decided it was time to work out how to build a business plan We went back and from the tinker- say something to the public. I rang a for a company that could take ARM ing that Sophie had been doing with journalist and said, “We’ve been work- out. Acorn’s desktop PC business was instruction set design, which Her- ing on this microprocessor design and not big enough to support proper pro- mann had entirely supported and ap- we’ve got it working.” He said, “I don’t cessor development; we needed a big- proved of, we put the project on an of- believe you. If you’d been doing this, ger market, so I tried to work out how ficial footing. I’d have known.”, and put the phone to spin out a company. I could never The other infrastructure aspect of down. [laughs] We’d actually done this get the numbers to work. You have to this is that from the Cam- in considerable secrecy; the secrecy was sell millions before the royalties start bridge Computer Lab, who was a direc- so good that we couldn’t even persuade paying the bills. We couldn’t imagine tor at Acorn, had persuaded Hermann people when we got the working silicon selling millions of these things, let that if he was serious about staying in in our hands. In terms of timescale, this alone billions, which is where we are the computer business, he needed to was all happening at exactly the time now. But a lot has happened to make get serious about chip design. Andy when Acorn was going bust and being that happen—it hasn’t gone there on advised Hermann to get chip design rescued by Olivetti. I believe Olivetti its own. When the company was spun tools from VSLI Technology, and Apol- wasn’t told about the ARM when they out, was brought in, and lo workstations. They recruited IC de- bought Acorn. When they bought it, he and the team evolved this business signers, a group led by Robert Heaton. we thought, maybe it’s time to own up: model, which has been instrumental I can’t remember precisely the order in its success. Had Apple not come they came in, but Jamie Urquhart came knocking at the door wanting the ARM early, Dave Howard, Harry Oldham— My strong memory for the Newton, and Robin Saxby not all names still associated with ARM. So been brought in to head it up...You we’d got these tools and the IC design- is walking out of know, there are lots of ifs. ers, but no chips to design. Sophie and there saying to If these things hadn’t happened, I were thinking we should have a go at we wouldn’t be where we are today. designing our own microprocessor. each other, “Well, But where are we today? I’ve been try- We looked at this RISC stuff, and if they can design ing to work this out. I suspect there’s thought this is kind of obvious, this is more ARM computing power on the a good idea. So we’ll set off using these a microprocessor, planet than everything else ever ideas and try to put something together. so can we.” made put together. The numbers are But it’s clear that big industry has got far just astronomical. more resources; they’re going to pick up on these ideas too, we’re just going to Copyright © 2011 The Centre for Computing History; get squashed underfoot by big indus- http://www.computinghistory.org.uk

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