Oral Histories of Semiconductor Industry Pioneers
Interview with Marcian (Ted) Hoff
March 3, 1995
Los Altos Hills, California
Hosted by Rob Walker
Co-Founder, LSI Logic Ltd.
Transcription by Dag Spicer
Program in History and Philosophy of Science
Department of History
(c) 1996 Stanford University Libraries
[Start of Tape: 0:00]
[Garden tour omitted approximately 3 minutes.]
[Start of Interview: 3:04]
RW: Today we're visiting Ted Hoff in his Los Altos Hills, California
home. Ted is often credited as being the inventor of the microprocessor.
I knew Ted while I was at Intel from 1971 to 1980. I considered him one
of the most brilliant semiconductor scientists of our time. This [interview]
is a part of the Silicon Genesis program and is part of Stanford's
Silicon Valley program. So, Ted, thanks for taking the time to give us
First, could you tell us a little bit about your early years, before
you went to Intel.
TH: Well, I don't know how far back you want me to go but I was
born in 1937 in Rochester, New York, and I got interested in science at
a fairly early age, primarily because my father's brother, who was
just 12 years older than I was, was studying chemistry and chemical engineering.
So I thought that looked like a marvelous subject. I loved the magic you
could do with chemistry and pretty much decided to follow in that career
until my uncle advised against it. He said that unless I went into chemical
engineering, as opposed to chemistry, he thought the job market didn't
look very good.
Now, partly because when I was twelve years old my uncle had given me
a subscription to Popular Science magazine and I answered an ad
for an Allied Radio catalog, I'd gotten interested in electronics.
So that was sort of my second choice and so, well, when it came time to
go to college, maybe that's what I should pursue...
So I went to Rensealler Polytechnic Institute. I studied electrical
engineering there and I graduated in '54. And then, not ever having
been west of Niagara Falls, I thought it was time to see a little bit more
of the country and decided to do graduate school and I was fortunate to
be accepted at Stanford University. So I came out to Stanford, got my Ph.D.
there in 1962 and I stayed on working with Professor Bernie Widrow in the
area of neural networks. And while I was at Stanford, I got interested
in integrated circuits. I had been interested in computers for some time
and we used computers in our work on neural networks.
So one day, I think it was around some time in early 1968, I got a phone
call. It was from a fellow who I didn't really know, but I had heard
of him, and I met him once I believe--his name was Bob Noyce. And he told
me he was starting a company and would I be interested in possibly becoming
an employee of his new company? Well, I thought it might be fun to try
and I interviewed, and got the position, and became employee number twelve
at Intel Corporation.
RW: Now, what was "Intel" short for?
TH: Well, I guess "INTegrated ELectronics." I don't
think I ever heard it explained. But, Intel started out with the idea of
building semiconductor memory and, in fact, when I was being interviewed,
Bob asked me the question: 'What did I think the next area for semiconductor
development should be?'... and I had been thinking about this a
bit and had talked to a few people and I said 'memory,' and
I guess that was the right answer because that was what Intel was planning
RW: That's interesting. Now in your class at Stanford, there
were a lot of other people that... was Shockley teaching there at that
time or had he left?
TH: I don't know whether Shockley was teaching there at that
time. I never had any courses from him but when I came to Stanford, there
was a fellow there, Dr. John Moll, who had been at Bell Labs and when I
was at RPI I had heard of him through some papers which were very important
references for I thesis I did. So I was pleased to find that he had joined
the Stanford faculty when I came to California.
RW: Well, Paul Low was there... went on to fame at IBM...
TH: Yes, Paul was in the same group that I was in working with Bernie
Widrow in the area of neural nets and adaptive systems, and adaptive filters.
RW: Jim Kofort and Ed Jones who were the guys who essentially invented
computer-aided design for ICs.
TH: Yes, there were also in our group and we were all working in this
area of neural networks at the time.
RW: Which kind of went away for a while.
TH: Well, it went away for a while but it's popped microprocessor
again recently. In fact, a few years ago I was invited by Bernie Widrow
to sit in on a study that was sponsored by DARPA of the state of neural
RW: Well anyway, so you're at Intel... so what were your first
TH: Well, my duties were primarily what they... they gave me the title:
"manager of applications research," and it really had two...
two areas. One was to help customers use products developed by the company,
which is the traditional 'applications' role, but the other
part of it was to talk to customers and find out more about what they were
trying to accomplish so that I could play a role in helping to define the
next generation of products.
RW: So, how did the microprocessor project get going?
TH: Well, that's... One of the characteristics of most of the
products that were being developed at Intel is... they were what we call
'proprietary' products. The [customer's] company had ideas,
defined the product, and started the development. And Intel also had a
policy of not really saying very much about products that were in development.
So that meant there could be a very long design cycle. From the time you
start to do the engineering until you release the product, then the customers
start to look at it, it takes them a while to design the product
in, and that can mean there is large investment being made in engineering
and very little in the way of revenue being derived from it.
So, at one point it was felt it would be desirable to undertake some
custom developments where you work closely with your customer, develop
the product to his specification. And one of our first programs
which started... let's see Intel was started in... well, officially,
I guess it got started about September of '68... and about April of
1969, we undertook to develop a family of chips for a Japanese calculator
company. And there were several names that this company used, different
corporate entities, but the calculators were to come out under the name
So, the contract was signed, the engineers came over from Japan to work
with Intel, to wrap up the last details of their design, and they arrived
sometime around June of 1969. Now the only role I was supposed to take
was to work with them and just help them find whatever supplies and so
on they might need and sort of act as an interface, or liaison for them.
But, in the course of that, I began to see that there could be some
real problems with the design they were proposing. There were some
pretty aggressive cost targets, part of the problem was that they were
going to be using, like 40-lead packages--those were expensive packages
at the time. And so, I was concerned that it was going to be very difficult
to meet the cost objectives for the program. So, it seemed to me that there
were some characteristics of their original design that were quite positive.
For example, they used read-only memory to customize it, but it didn't
seem to me that they were making very effective use of the read-only memory.
The level of program they put in the memory was a very high level program
which meant that there was an enormously complicated logic to implement
the actual functions of the calculator family.
So, my first suggestion was just 'why not make better use of that
memory by simplifying the functions that you're going to perform
in the calculator and do more with the read-only memory?' They weren't
very interested in making any changes, the Japanese engineers were committed
to the design they had and they essentially told me to stay out of their
way. But Bob Noyce was encouraging, and so I continued to work on that
and actually in the course of that, over a relatively short period of time,
felt that the way to do it would be to make a very simple, general purpose
computer. And I started to develop the instruction set for that computer
and that instruction set was essentially what became the instruction set
for what we announced as the "4004" microprocessor.
But with that instruction set I was able to show that it was possible
to scan a keyboard, debounce the keyboard--in other words, you do multiple
scans and check to make sure that you get consistent results on successive
scans--to maintain a display, and to do the calculator arithmetic. And
that would be done, and my thinking was to do it in binary, but with a
binary-coded decimal correction so that you could binary or binary-coded
decimal arithmetic. And again, I worked out that instruction set and a
configuration which was initially to have two chips that would make up
the central processor. There would be essentially a central processor and
there was a timing chip that was going to generate sort of timing for the
whole system. And then there was a read-only memory chip, to be developed,
and a read-write memory.
And again, the idea was basically rejected by the Japanese engineers
but again, Bob Noyce and others at Intel, encouraged the development. And
eventually it went to the point where... I believe it was in September,
actually September 16th and somewhere I have a letter, in which we made--our
marketing department made--essentially a formal proposal to the Japanese
that they consider this Intel design as opposed to their own engineers'
And Japanese management came over from Japan, and I believe that was
in October--I don't know the exact date--but sometime in October
'69 and essentially both groups presented their approach and my group,
which at that time consisted of myself and Stan Mazur, essentially proposed
this general purpose computer approach. And one of the advantages we pointed
out was that it wasn't limited to just calculators but it had other
applications as well. And so, it turned out much to our surprise and delight
that the Japanese management agreed and chose the Intel design as the one
to be pursued, and so as of October of '69 we were committed to build
what would be a computer on a chip. And in the course of the subsequent
refinements of the design, the timing chip was combined with the central
processor to make a fully stand-alone central processing unit. They only
thing it required were a couple of clock signals and power supplies.
RW: So, how long did it take to get silicon?
TH: Well, the big problem was I was not an MOS designer. And it would
have involved a lot of training and I had other obligations as well. I
did do a brief study from what little I did know about MOS to estimate
the number of transistors that would be required--to make sure that we
were within reason and it looked like it would be somewhere around 2,000
But Intel only had a few people who were capable of MOS design and so
they started to do some recruiting. And it took almost... well something
like six months before they found somebody and then, I believe it was April
of 1970, when Federico Faggin finally joined Intel. I believe he had been
at Fairchild before that. Federico worked at just a furious pace, I mean,
he really, really went all out and in the space of about nine months, designed
the three major chips. And by that time we actually had four chips that
were defined. One was a very simple static shift register that was just
used as an I/O-expander. But there were three complicated chips to be designed:
a central processor, a read-write memory, and a read-only memory. And both
the read-write and read-only memory had I/O ports on them, so they were
more complicated than just a simple memory chip would have been.
I believe the last one that Federico did was the 4004, and I think he
had first silicon on that sometime in January of 1971. There were some
problems and he fixed those and second silicon, I believe, came out in
February of '71 and the processor worked at that time.
RW: And that was the microprocessor.
TH: That was the first microprocessor, yes.
RW: How exciting. Of course, you guys didn't realize you were
making history at that time...
TH: Well, probably not that we were making history but that we felt
that it was important. And one of the things that we did realize was that
we were... a lot of us... that included some of the engineers, Federico,
and myself, we had various projects going on in the lab and we realized
that if these chips were available it would make our ability to design
things like test equipment and so on... it would make it a lot easier to
have those chips available. And, in fact, one of the projects I had was
to build a ... I guess what you'd call a 'PROM burner,'
but a device for blowing the fuses in a bipolar PROM or programming the
floating-gate devices... of course about that time the floating-gate EPROM
was being developed by Dov Froham-Benzkovksy who was at the next bench
at Intel. It turned out that was a very fortuitous development because
those EPROMs turned out to be very useful devices to help complete developments
that used microprocessors. The microprocessor, we felt, was very important
in the sense that engineers would find it a useful device, and it
would make design easier, and allow you to do things that you couldn't--or
would be reluctant--to do in a design done with conventional logic.
Things like the interface to the human being. We could do things with
the microprocessor like not allow you to set the switches in something
in a way that would be destructive to the equipment. It's much harder
to do that when you are just, you know, providing switches to, you know,
to somebody and they can flip them in any manner.
RW: Well, today when we think of a microprocessor we think of something
that sits on a desk, that is, a computer. Yet the first ones were really
controllers were they not?
TH: That's correct, they were controllers and our imagined
use for them was in the area of controllers. In fact, the kinds of things
that we talked about--applications for microprocessors--were things like
elevator controllers were the example we used to give ... but we did have
applications of that type. People, I believe, were using them for ... like,
gas pumps, in other words for gasoline stations where they were starting
to have centralized gathering of information--what was going on at the
pump--so, in effect, having a small processor available for that application
was really ideal. And things like, you know, traffic control, traffic signals,
the counters and so on for control in parking lots... So those were the
kinds of applications that we envisioned the parts for.
At that time, we weren't really looking to replace the general
purpose computer. For one thing, the microprocessors of that first generation
were very slow devices and if you were to go to an application that
required a large amount of memory, you were going to have to have a big
investment in memory, because memory was quite expensive then. So it wouldn't
necessarily make sense to use a microprocessor in that environment because
you weren't using your memory effectively, you might do better to
spend a few dollars more and use a processor that was built out of TTL
such as you'd find in a minicomputer of the day. So, for that reason,
we tended to limit our imagined use of these devices to applications that
could be done with very modest amounts of memory.
RW: Now did BUSICOM ever build the calculator?
TH: Well, BUSICOM I believe did build some calculators but BUSICOM had
financial problems. They were always cash-short, and I believe they were
not able to really successfully market the product so they didn't
use the volumes that they expected. And in fact, one of the aspects of
that... originally, Intel marketing was very reluctant to offer the products
to anyone other than BUSICOM. The feeling was that BUSICOM would
use the entire production that Intel would be capable of manufacturing.
But there were a number of us there who felt ... I was one, Federico was
another ... who felt that this product was much more useful than just for
calculators, that other people would find it, and that Intel should offer
it as a proprietary... you know, an Intel proprietary product. The only
problem was that when the contract was written with BUSICOM, even though
it was totally an Intel, in-house design, the contract was written in such
a way as to give BUSICOM full rights to the product. So it was actually
necessary to go and negotiate a new contract, and, in fact, BUSICOM opened
the door in May of 1971 when they said that the calculator business had
gotten so competitive that they wanted to see if they could get
lower prices for the parts than they had originally negotiated.
At that time, I know I was one who went to the marketing people and
said: 'If you can't get any other concession from them, at
least get the rights to sell it to other people.' And the marketing
people were very reluctant to even consider that as an option, but
they did. And they did get the rights--with certain restrictions, there
was a restriction that said 'couldn't be sold to other people
who were manufacturing calculators.'
RW: Now, was that Ed Gelbach, when you're talking marketing?
TH: No, this was before Ed Gelbach came to Intel, in fact, the director
of marketing at that time was Bob Graham. And, I believe the... I don't
know his exact title but sort of like, uh, you know, very high up in the
marketing group... was also a fella named Bob O'Hare. And, I mean,
both of them, essentially told me that it was difficult enough to find
salesmen to sell memory products and to hire them into a semiconductor
company and they felt that it would be impossible to hire qualified people
to sell computers. And so for that reason it was not reasonable to consider
having the company go into the computer business.
And furthermore, they felt that the, in fact, one told me... I don't
remember which one it was who told me this but it was one of the two gentlemen,
said something to the effect that 'look, we're late
coming into the computer business... we'd be lucky to get 10% of
the market. Now they sell maybe 20,000 minicomputers a year. That would
be 2,000 chips a year and for 2,000 chips a year, it was not worth all
the headaches that you would have if you had to support computers.
RW: And of course that goes back to the first mainframe computer. The
initial estimates were that you could sell somewhere between ten and a
TH: I might point out that one of the three engineers from Japan, a
fellow named Matsotoshi Shima, gave a talk a few years ago and he quoted
the use of microprocessors and microcontrollers in Japan and the number
he quoted was 600 million...
[video edit drop out approx. 0.5s]
RW: ...to get the 4004 to market?
TH: Well it took actually quite a while for us to get the 4004 to market.
Now, we had the rights to sell it as of May of 1971 but there was great
reluctance, not just in marketing but elsewhere in the management of the
company to take it to market, and one of the big concerns was how we would
support our customers. In fact, it was felt that this could be a real problem.
There was a concern about, you know, how even the sales force would handle
So we were developing some tools, things like assemblers and the like,
and we managed to have some contacts with some universities that also provided
some tools for us, and we went outside also for their development. We were
developing some design aids for our own use in-house, and we felt that
those would be useful for our customers. But, I finally took the position
that we'd probably just have to let some of our customers be on
their own but we could probably support maybe a dozen or two dozen of the
largest of them.
One of the factors, though, that I think really helped get the microprocessor
announced was a change in the marketing department. As of, I believe it
was August of 1971, a new director of marketing came on board. That was
Ed Gelbach and he came from Texas Instruments... and apparently was not
nearly as afraid of the microprocessor, and he may have been aware of some
developments that were going at Texas Instruments that we didn't
know about at the time but subsequently found out about those developments.
But anyway, Ed was much more open and, as of, I believe November of 1971,
a formal announcement was made. And in that announcement--it was not a
modest ad--the statement was made 'Announcing a new era in integrated
electronics ... a microprogrammable computer-on-a-chip.'
Now we debated a lot about using the word 'microprogrammable'
because microprogrammable normally meant that the order code was something
that could be adjusted... but there were those that said that 'no,
"microprogrammable" really meant that the code was cast in
some form of firmware.' And in that sense, we figured, well we could
use the term.
The ad was placed and there was a Fall Joint Computer Conference at
which Intel had a suite, and Stan Mazur went to that conference and was
at the Intel suite and he said customers came in and they were indignant
having seen the ad, and he would show them a copy of the data sheet that
Intel had produced and the customer thought it was, you know, probably
just another 4-bit slice. And the customers would see the data sheet and
say 'It really is a computer,' and they were satisfied. In
fact I have a copy of the first data sheet that we produced and this was
also considered... it may seen very trivial today... but the design and
the layout of this data sheet was considered, by our marketing department
anyway, to be revolutionary. And the reason is that the first part of the
data sheet is all application information and it isn't until you
get to the back part of the data sheet where you get to the electrical
specifications. And up until that time, it was traditional that the data
sheet started with the electrical specifications and ended
with the application information. But the feeling was that when you are
producing a computer central processor on a chip, it's the application
information that's more important than the electrical information.
TH: And that's why it was put first.
RW: Well, of course, earlier semiconductor products--their use was more
TH: That is true.
RW: You know, if it's a RAM, it's pretty obvious what
it does but something like this, it's not clear what it would be
used for initially. By the way, one of the other ramifications of that
announcement was it put me out of the ASIC business because I was producing
calculators and various application-specific ICs that the customers saw
that the microprocessor could replace that, and so my group got canceled
and I had to go to a different type of work and everything... So you're
responsible for that!
TH: Well I think of that as somebody overreacted. We always felt that
the microprocessor wouldn't replace the ASIC business itself but
maybe it would cut into the bottom end of it. Because where we saw it as
primarily having application was in the realm where you couldn't
afford to do an ASIC design where the engineering cost would just
wipe you out. And in that case we felt the microprocessor will make a ...
will find a niche for itself. But it still looked like it would be well
worth it when you get into very high volumes to go to the ASIC ... so I
think somebody overreacted in that case.
RW: [laughs] Well, now, were you involved in the 4040?
TH: Uh, not in the 4040 but there was a second, parallel development
actually that went on at Intel and I was somewhat involved in that, and
that led to the 8-bit processor, the 8008. And, in fact, it started very
shortly after we had that meeting in October of '69 that got us committed
to the 4004. I think it was around December of '69 ... we had a contact
from--actually, Victor Poor of Computer Terminals Corporation--and I believe
they were a user of shift-registers and they were building what they sometimes
referred to as 'glass Teletypes,' computer terminals that used
a cathode-ray tube instead of paper to, you know, present the information.
And his initial request was for the registers of a machine that
they were to build and I believe his original contact was primarily to
Stan Mazur who was working for me at the time.
In the course of that, it seemed that to understand, first of all, how
the registers worked, you needed to understand the processor and the processor
was really not that much more complex than the 4004 processor. So, we made
essentially a formal proposal that they let us do their whole processor
as a single chip. Stan described it to me, he said Victor Poor nearly fell
off his chair ... Subsequently to that, Victor Poor has said that he
brought the idea for the microprocessor to Intel and that it was his intention
all along to do it as a single chip.
But considering that the 4004 had already been defined, and we
considered the 4004 to be the first microprocessor, and it was really...
my firm belief is that the original request was for registers and it was
our counterproposal to do the eight... well, what was ultimately
known as the 8008 ... it had different number in the early days--it was
called the "1201" within Intel for throughout its development
cycle. And that essentially was launched officially as a project around,
maybe around February of 1970, and the engineer who worked on that was
a fella named Hal Feeney, but he was also working with Federico Faggin.
And so the work on that product went a little bit slower and, at the time,
Hal was not as experienced an engineer, so I think Federico was working
faster, moving along faster on the 4004.
So, then Computer Terminals got into some financial difficulty and so
they apparently were not even likely to use the product---in fact, they
never did use the product--but when they had written the contract with
Intel to develop the product, they did give us the rights to sell
that to other people. And we did have, I believe, contacts with
Seiko of Japan as one of our early customers.
That product led to some rather interesting side issues having
to do with intellectual property. In the case of the 4004, we felt that
was an Intel proprietary design and therefore we thought it would reasonable
to try to protect it. We spoke to our patent attorney, a fellow whose name
was Stuart Lubitz, but Lubitz said he did not want to write a patent on
a computer. He said they weren't worth it and essentially he refused
at that time to write a patent.
And I can see why. Subsequently I came across the patent that was written
on the IBM 360 computer and it runs something like, I think it's
around 900 pages of drawings and another 900 columns of text, or something
in that order... it's an enormous document. We said that it's
too easy to design around a patent of that type. And I think he felt the
idea of putting the computer on a chip was a fairly obvious thing to do.
People had been talking about it in the literature for some time, it's
just... I don't think at that point anybody realized that the technology
had advanced to the point where if you made a simple enough processor,
it was now feasible.
RW: Well, that's right, the idea had been kicking around but
the technology wasn't there and in fact...
TH: That's right...
RW: ... in fact, Hal Feeney came to me at... I was at Fairchild... and
he said 'we were working on this microprocessor' which turned
out to be the 8008, 'and it's going to take us a long time--we're
doing this design all by hand... Can you do essentially a silicon breadboard
using your standard cell technology.' And I looked at it and I couldn't...
I couldn't do it... it would have been four or five chips...
RW: ... to do, because the efficiency... and we also didn't have
as good a process. So while the idea was there, you had to have a ... Intel
really had the hottest process around.
TH: Yes, we figured our process was probably good for maybe twice the
transistor count of any other MOS process around and, of course, the MOS
process had about a four-to-one advantage on logic density... so no that...
definitely... we felt we were... we were ahead in that sense and that's
where we felt we had a good shot at being the first to make a microprocessor.
There were other papers, I mean, that were written... I think I've
seen one as early 1965 talking about a computer on a chip, but it was recognized
that until yield problems were solved, it was a long way off.
And, in fact, I've published an article in March of 1970... this
is the 1970 International Convention Digest and this, as far as I know,
is the first mention of the feasibility of the microprocessor in
which, I said in here that ... um, the article is called "Impact
of LSI on Future Minicomputers," and it said "an entirely
new approach to the design of very small computers is made possible by
the vast circuit complexity possible with MOS technology. With 1,000 to
6,000 MOS devices per chip, an entire central processor may be fabricated
on a single chip." So that was essentially announcing there the ability
of the technology to do a one-chip microprocessor.
RW: It's also interesting how fast things move. That was in 1970,
we're filming this '95, and now there are so many billions
of these around the world. One third of American families have a personal
computer in their home.
TH: And now people routinely put several million transistors
on a chip and we thought we were lucky to have from 1,000 to 6,000. That's
where the technology was in those days.
RW: So the 8008. Were you involved with that?
TH: Well, to a degree in the definition. In fact, Stan and I one day
were talking and the 4004, you see, did not have interrupt capability.
Now an interrupt is something where you have a computer and it's
doing a task and you have this interrupt circuit which allows an external
event to signal the computer, the computer essentially stops what its
doing, goes off and does a new task, and then picks up where it left off.
So, we thought 'wouldn't it be nice if we could put interrupt
capability into a processor?'
The 4004 didn't have it. The only way the 4004 could deal with
I/O was through polling and by that it means that it keeps going
out and sort of doing a conditional test that says 'is there anything
out there for me to do?' And then if the answer is 'no'
it goes back to what it was doing but it has to have that instruction programmed
into the loop to check to see if there's some I/O operation pending.
RW: Of course, that's appropriate for a calculator.
TH: That would be reasonable in that environment. So we thought
it would be nice to put in an interrupt but we did not want to add significantly
to the complexity of the chip. So the question is: 'what's
the least that you put on the central processor chip so you can add interrupt
later on as an afterthought. And we came up with what we thought was a
really novel solution. The idea was that we felt that we could put a switch
between the processor and its memory. And on interrupt, we would, essentially,
flip the switch and have it read a different instruction. In other words,
instead of reading from memory, we'll force, force a CALL instruction,
that's a jump to subroutine. So once you forced a CALL to a subroutine,
then the subroutine supposedly can save the state of the machine and it
can, you know, do the interrupt task and then RETURN like any other subroutine
RETURN does and it goes back and picks up where it left off.
Only one problem: the processor was asking for something from memory
when we flipped that switch. And it's got a program counter that's
keeping track of where it's fetching from memory. And the program
counter has been advanced, so it's been advanced as it fetched the
CALL instruction, so it's going to miss a few bytes out of memory,
what it shoves on the stack as part of the subroutine CALL is not gonna
be the right number. The solution is just don't advance the program
counter when you're forcing this CALL instruction.
On interrupt, at the end of the current instruction, interrupt is acknowledged,
during interrupt acknowledge the program counter isn't advanced.
We didn't say what it was to be used for... that's all we
wrote into the spec.
Well, this spec was essentially for our customer, Computer Terminals.
And Computer Terminals Corporation, we didn't know at the time,
was looking to Texas Instruments as a second source for their products.
So they took the design to Texas Instruments, which was fine--I mean, it
was their right to do so--but what I do have a problem with is Texas Instruments
proceeded to file for a patent on it.
Now we would have considered that unethical, for one thing the architecture
of this machine was supposedly Computer Terminals' with a few, you
know, assists from Intel in terms of how it interfaced and so on to get
it down to... it ended up in an 18-lead package.
But anyway, it's interesting... Texas Instruments included that
business of the interrupt handling by not advancing the program counter.
But, it turned out in subsequent work with this product at Intel ... as
Stan and I (and our responsibility was applications, you see, not the design
of the chip) ... we began to realize that even though we had this nifty
little interrupt technique, it was going to take a lot of logic to force
a CALL instruction because a CALL instruction was three bytes and that
meant logic that had to take over from memory and then figure out how to
sequence through these three bytes to set up the CALL.
But there was another instruction in the repertoire that was called
RESTART. Now, the RESTART, as originally defined in that first data sheet,
ah, first you know, target spec, was not a CALL instruction. It was just
like a jam-load of the program counter to an initial value. But we thought
about it and we said 'what would be the harm in making RESTART a CALL
instruction, where the program counter is saved on the stack?' It
just means that if you want to use it like a RESTART, you just never going
to do the RETURN that would have gone with the CALL. So that doesn't
hurt anything. You use it like a JUMP and you just don't bother
to RETURN from it.
And the way the ah... it wasn't like it was going to waste memory
because the stack, where you saved these RETURN addresses was actually
a ring, like a toroidally-connected ring of memory. So, um, it essentially
didn't matter where it started in the ring.
So we made that change to the spec. Now apparently, that piece of information
never got to Texas Instruments. So when they wrote their patent application,
they did find out that Intel serviced an interrupt by forcing a RESTART
instruction. But the RESTART instruction in the TI chip is not a
CALL. It's a jam-load of the program counter--so it's non-functional--yet
TI wrote that into their patent. So, in effect, it's fairly obvious
that the people that wrote the TI patent didn't even know what they
But TI did assert some of those patents in recent litigation. And, however,
it has come out that information showing that a lot of the information
on some of those patents was actually copied from Intel. And I understand,
as that information came out, they got very reasonable in their licensing
negotiations! So as far as I know, it has not gone into court but it has
been in to negotiation and it has gone very close to going to court.
RW: Well TI, in the last recession, the difference between their profit
and loss was their licensing fees.
TH: That's right.
RW: They became very aggressive.
TH: I've heard that also, yes.
RW: Well, so on the 8008 so you were ... you had some ideas in it and
then Hal Feeney implemented it. When was that introduced?
TH: Um, the product I believe was announced about April of 1972. Actually,
there was more of like a pre-announcement of that maybe a few months earlier.
When we came out with some of the literature for the 4004, we did mention
this 8-bit processor that was coming along. And the 8008, and... with those
exceptions of things like the interrupt and the RESTART instruction, was
primarily an architecture that had been developed by Computer Terminals
Corporation. They brought us the bulk of the instruction set.
And our customers began to... they tried to use the product... in other
words, if they had a little application they'd consider the 4004
but if it was a bigger application, they felt they should use the 8008.
And it wasn't necessarily the most reasonable choice because in
many cases the 4004 would do 8-bit arithmetic faster than the ... or multiprecision
arithmetic, faster than the 8008 could do, because the 8008 was a pretty
But customers wanted more processing power and it turned out that it
was kind of short of registers. So, it was ... even with our interrupt
scheme, it was difficult to really handle an interrupt. You couldn't...
you had to reserve registers, it didn't have the capability for
saving the state of the machine easily, and one day Federico Faggin came
around and said that Intel had this new n-channel process and that he was
going to lay out the 8008 in n-channel. And I asked him if it was just
like a, you know, a simple, re-photographing or whether it required a new
No, he said, it was going to require a totally new layout, all different
design rules. And so I said 'Well how about if we fix some of these
problems we're hearing from our customers?' and so he was
receptive fortunately to that. And so, really Stan and Federico and I all
contributed to what ultimately became the 8080. And I consider that the
first microprocessor that really had performance comparable to a
minicomputer and I still think of it as one of the first really successful
microprocessors... I had lots of second-sources, in fact, I heard even
that the Russians built a copy.
RW: OK, let's stop for a moment.
RW: Well, certainly you became officially known as 'the guy,'
the guy that invented the microprocessor, and you were in Fortune
magazine and so on and so forth. And yet, Federico Faggin and Stan Mazur
were also involved. Was there any hard feelings from their standpoint?
TH: Well, I know Federico has had hard feelings. One thing... I've
tried, most of the times, when I have been recognized, to give credit for
both the role that Stan and Federico made. I mean Federico, there's
no question, he did a fantastic job of layout and nobody should take that
away from him.
However, I think if you look at some of the time frame, I believe originally
it was probably Gordon Moore who was responding to Fortune magazine...
You know, 'how'd this thing get started?' And it was
started by me, before either Federico or Stan was an employee of Intel.
Stan joined in September of 1969. This thing got started by me before that
time frame and, in fact, it was like the 16th of September when we made
essentially a formal proposal to Japan. But the work had been going on,
essentially, from about the beginning of July and it was throughout much
of late-July and throughout August that I was working on this basic idea
and the instruction set and so on for the 4004.
Now, it was difficult however, working alone and especially ... I had
the Japanese engineers who were hostile to what I was doing so it
was wonderful when Stan joined the group--which now was two people instead
of one--and began to make contributions. And Stan did make a lot of contributions
to the basic ideas for the processor. But, I think, why I got singled out
in this by the people at Intel was because I really did start the thing
before either of these other people joined.
TH: Federico didn't join until the following April. On the other
hand, Federico did do the detailed circuit design and the full logic
design and layout for the part... he did a lot of work and he deserves
the credit for that. But, as far as the architecture... which I feel...
the architecture is a crucial factor in getting the transistor count down
to where it would be compatible with the process of the day. And
in fact, that part of it... you know people were projecting something like
thousands and thousands of gates that would be required. Now figuring something
in the order of three or four transistors per gate, you'd be talking
20 or 30,000 transistors for many of the architectures that might have
People were looking at using LSI for aircraft computers and they
were talking about doing it in LSI but maybe twenty or thirty chips...
so the idea of getting it on... an architecture that would get it to one
chip was, I believe, a crucial factor and I still believe that that's
one of the simplest architectures around. The actual transistor count ...
when you count the physical transistors on the die, I believe it's
a little over 2,100 ... I think something like 2108. When Federico counted
the transistors, I think he counted it as 2,300 but he said in that he
had some regular arrays and he was counting transistors that he didn't
actually implement--sort of like a read-only memory chunk in which he counted
all the sites as a transistor even if a transistor wasn't
But I mean this was a very small number. One other point on this is
that the basic definition of what became the 8008--its instruction set,
its register complement and so on--that device ended up, I believe around
3,400 transistors and, as far as I know, the TI device was designed from
that same spec. In other words, as far as I know, there was no flow of
layout information, or logic detail from Intel to TI. It was just
an overall architectural viewpoint ... bus specifications and things like
that that went to them. I believe that their transistor count ended up
just a little over 3,000 as well and there were a few features that we
had added to that original instruction set, for example, making the RESTART
So, the architecture is really what determines the number of transistors
and I feel that's what really made it possible to do the
device at that time.
RW: Well, and I think most people would say that the architecture is
the machine. Because it can be implemented in various technologies and
that's sort of a turn-the-crank kind of thing...
RW: ...that the real definition of a computer is the architecture and
TH: And along those lines, I might mention there's a situation
with a patent granted to a fella named Gilbert Hyatt. Now he filed nine
months after this IEEE article appeared [holding up previously-mentioned
article]. He had a processor that he was describing built with TTL... I've
seen the patent application, the original application, the processor was
actually working with a core memory but he said it could have been replaced
with semiconductor memory. There is nothing in the disclosure of the patent
that says anything about single-chip technology. The patent had something
like 140 claims and one claim in the patent application said 'I
claim this processor implemented as a single chip,' which would
be reasonable in the light of the article that had been published nine
Now, the only problem is that if you look at the design that's
published there and go back and do a transistor count--and I made that
effort--using what I consider a very conservative design effort in which
every gate was a complex gate and that way you minimize the transistor
count, I still came up with something like almost 8,000 transistors for
the processor. But then Hyatt's patent claim says that the memory
is also going to be on that same chip so if you make that
assumption and the type of memory that was available then, if it was read-write
memory would be... was six transistors per bit. So in effect... and that
would have been something like 32,000 bits of memory I believe was the
number. So it would have been a very, very large amount.
RW: It would have been impossible.
TH: Yeah. And even... I believe even the seven thousand or eight thousand
transistors for the processor would have put it out of the realm of possibility
for this time frame...
RW: It would have been a number of years before that would have been
TH: Yes. But that probably would not... and it's not realized
by the patent office, probably nobody in it would appreciate it...
RW: What's happening with that now?
TH: As far as I know, that patent has been asserted and royalties are
being paid. In fact, not long ago, I was looking at a small notebook computer
and happened to notice that it said on the computer itself, it said 'licensed
under the following patents' and there was a list of patents. So
I looked up the patents and they were all Hyatt patents, and including
the one that supposedly covers the microprocessor.
TH: The other thing that's also interesting, some of them covered
the idea of refreshing a dynamic RAM. It was actually put in... and what's
interesting, there's not a word about dynamic RAM. And in fact,
it seems fairly obvious from the wording in the original patent application
that when it was filed, Hyatt didn't know that dynamic RAM existed.
He talks about read-only memory or flip-flop memory and dynamic RAM is
RW: So, have you ever looked up this attorney that wouldn't patent
TH: There have been several times when I've almost crossed paths
with him. I'm not sure he would admit at this point to his role
in the matter...
RW: Well, you went on to do a bipolar bit-slice...
RW: and that was the first bit-slice...
TH: Well, I don't know...
RW: ... AMD's followed.
TH: OK, I didn't know that. We attempted to do a bit-slice and
Intel did not have a strong position in its bipolar technology at that
time. We had an early start with the Schottky process but it really didn't
develop and progress as much as the MOS processes did.
So, in looking at it, we felt... in fact, we never intended to offer
a bit-slice. In fact, we considered that the worst nightmare would be to
try to support a microprogrammed architecture. Because then, in effect,
you're trying to support everybody doing everything. In fact, we
had an architecture, an actual processor defined, that would have essentially
directly implemented the code that was put out by Intel's PL/M compiler
and that's what we thought we would build with our bipolar
family. We had optimized the design for that particular processor and I
guess there must have been a recession sometime around 1974, or about the
time this was coming out, and Intel decided no way did it want to support
another processor family and so the chips were designed and ... but there
was no intention to do an upgrade. Because the idea was this would have
been an upgrade path... if they 8080 wasn't powerful enough for
you, then you go to the bipolar processor. So that, it was decided, would
not be announced. And then we... Now we were in that nightmare scenario:
what do we do with these chips?
And so they were announced. In fact, I had written a... what I considered
a crude assembler for the microcode so that I could, and the engineers
working for me, could generate microcode for this family. But it was not
a clean layout. I mean, I threw this thing together and it worked fine
for us but I felt that before it was offered as a product, someone should
clean it up. There was a software development group at Intel that was supporting
the microprocessors and so we sent the product over there... or this assembler.
Well, they decided that they would not only re-write it but they would
totally change the assembly language. So now we were in the situation where
we had the product on the market and we didn't even have an assembler
for it. I mean, we had one working in-house but what they published as
an assembly language was not what we could run.
And of course, they were months late on getting the product out, so
that did not help. And of course people came out with 4-bit slices... we
figured about the best we could yield was a 2-bit slice. We did
try to compensate by putting some of the interfaces that you do from that
2-bit slice... you know, the bus interfaces so we could have the address
bus and the data bus from that same slice. Where in some cases with the
4-bit slice, you'd need to have separate chips outside that would
buffer an address for an address bus. But, generally, one of the things
I found: you can't really tell the customer what he doesn't
want to hear. And he just knows that a 4-bit slice is better than a 2-bit
slice, even if it needs a bunch of logic to go around it to accomplish
the same function!
RW: Well, also at that time, Intel was exiting the bipolar business.
There weren't putting the R&D into bipolar.
TH: ...Our major effort was in n-MOS.
RW: Correctly so, ... it [bipolar] was sort of a lame duck.
RW: So you left Intel in what, '83?
TH: Well I had a sort of very different career at Intel for some years.
In other words, I really got out of the microprocessor game in about '75
and started with telecom activity. And I feel fairly... quite proud of
that activity because as far as I know, we produced the first commercially-available
TH: And our group, with a little help from Paul Grey from Berkeley who
came down and spent a sabbatical with us, we had I believe the first commercially-available
switched capacitor filter, that's an important product that supports
the CODEC. And then we had another product which... it wasn't the
right product at the right time but it was still, I think, a pioneering
device, a digital signal processing chip. In this case, it had analog I/O
on it, we called it the 2920, and we were looking to try to do things like
DTMF receivers, and MODEMs and so on with this device. But as I say, it
wasn't a successful product. In this case, the ASIC implemented
with, you know, switched capacitor techniques seemed to be more attractive
to the people. We never found the right market for the product that had
a small enough volume to justify a programmable part. Most of the things
like MODEMs ended up being high-volume things where they were well able
to go and do custom or semi-custom logic for.
RW: Yeah, and of course in those days telecom was primarily copper wire
was it not?
TH: Well there was copper wire but there was a developing interest in
switching and the use of ... well the CODEC was originally so that you
could multiplex conversations over a twisted-pair wire which originally
would have been installed so it'd carry one conversation, then by
digitizing and sending over that same wire, you'd go in and at each
of the places where there were loading coils you'd replace those
with repeaters to handle the digital signal and re-establish it, and now
you put 24 conversations on that same wire pair.
So, that's where the CODEC was to be used originally. And I had
the idea that it could also be used in a switching environment, in other
words, in a PABX environment where the signal coming in from the telephone
is digitized and then you do your switching digitally and then send it...
RW: Which, of course, is how it's done today.
TH: Yes. And so, designed into our first CODEC was some of the control
that one could use to do that kind of switching. Then, as you ask, I left
Intel in the beginning of 1983. I mean I'd been there for 14 years
... which I think is a long time in this valley... and Atari had made a
very interesting offer. They were working on a wide range of very interesting
things. I mean, some having to do with video games, some having to do with
home computers and in other applications of computers. They were looking
at things like picture telephones and ... one of their gadgets was a...
they called it a 'sports meter' for runners and joggers and
so on--making use of Doppler sonar--and a whole range of looking at the
ways you interact with a computer and trying to get data in more quickly
or mechanical reactions... things even like... for things like driving
simulators to get the feeling of the wheel and so on.
So there was a lot of engineering going on in that area and Alan Kay
was at Atari and in this case, I would be working fairly closely with Alan
Kay and some of these new R&D ideas and new ways to look at computer
applications and that sounded like it could be a very, very interesting
field to be in. The only difficulty was that, I think at the time I joined
Atari, I don't think anybody realized how much trouble the company
was in. And over the following year, that just magnified.
One of the things I had remembered about Intel was that when we came
out with a microprocessor, there was a major concern, which at first I
didn't understand but finally understood: a lot of microprocessors
were sold through distribution. And one of the problems was that distributors
were kind of lax about getting information about sales back. You didn't
know whether the product went out the door or whether it was sitting on
the distributors' shelves. So there were some major efforts being
made to improve the feedback about what's actually happening out
there under 'distributor's inventory.'
RW: And also, not to actually count it as a sale until a distributor
TH: Yeah, until it's in a customer's hands...
TH: Well, one of the things I found out was the attitude of Atari was
since most of their products were sold through distribution, there was
no way that you could have knowledge of what the final sales were.
So essentially they washed their hands of it and that came back
to haunt very badly because apparently there were a lot of games and so
on, out there on distributors' shelves that were not moving
and that the company didn't know about and assumed that they had
sold and they were making more. And so that was one aspect of...
RW: The company collapsed really rapidly.
TH: It ... the other thing was the market had probably just saturated. I mean, there was, there's probably a certain number of people or families that have--I guess the main market were teenage boys between what, a certain range of ages--which were the primary customer, and at some point every one of those families had, you know, the video game equipment. And unless the next generation offered a significant improvement, nothing much was going to... you know, they weren't going to buy another one.
And so in some sense, I think, they continued to project the same growth,
you know, sort of neglecting the fact that the market was... they hadn't
bothered to stop and count the number of kids that really were out
RW: Well we did that with watches and calculators. Traditionally we
just keep extending that growth... which doesn't happen.
TH: It's nice once you put the straight line on the chart just
to project it out there... you like the way the numbers look!
RW: ...On log paper!
TH: Yeah. So, I think that was a factor and so when it did start to
shrink, it was a very painful time... and necessitated a lot of cutbacks
and under those circumstances, the future-thinking... R&D and, you
know, these activities that Allan Kay was associated with and that I was
to be associated with, were really not considered high priority anymore.
I was given responsibility for some of the more immediate tasks to be
done at the company. But even those were seen as a problem. And as I heard,
the concerns began to grow at the parent company, Warner, and so finally
they decided to sell the company and it was purchased by Jack Tramiel who
had been associated with Commodore.
And, in fact, I was away in New York when the word came that the company
had been sold. In fact, I'd heard rumors about it before... I even
had spoken to some of the people there, you know, and the management, and
they sort of you know, pooh-poohed the whole thing. I don't think
anybody really knew that this was happening... except back at Warner [laughs.]
And so anyway, when I came back, I met with Jack Tramiel and who was
very pleasant but, essentially, we pretty much agreed that what he wanted
to do and what my interests were were probably not very close. And so,
at that point, they just bought out my contract and I became independent.
Shortly after that, maybe it was about a year, Gary Summers who had
been in charge of Atari Semiconductor and who also left about that same
time, decided to start a company in the ...in fact, he called it "TECLICON"
for TEChnical LItigation CONsultants... in which the idea is to provide
technical expertise to people who are involved in patent litigation or
patent prosecution. And it turns out that while the attorneys are very
sharp, there's a limit to how much of the technology they can follow
because they have so many legal aspects that they have to worry
So we found this niche and I found it fascinating because I often get
to ... sort of like playing detective, in other words, digging through
and looking for 'prior art' and the experience I've
had helps me a great deal in this. In other words, knowing where to look
for a piece of prior art or what type of technology might be using
something that's relating to a topic that'll be at issue
in a patent trial.
RW: Well did it ever come out that Babbage had really ...was really
TH: I don't think we've gone back that far.
RW: OK, well Ted, thanks a lot. We've got to wrap it up here.
But it's been great fun talking with you.
[End of Interview: 1:19:18]
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