Inventing The Microprocessor: The Intel 4004

We recently looked at the origins of the integrated circuit (IC) and the calculator, which was the IC’s first killer app, but a surprise twist is that the calculator played a big part in the invention of the next world-changing marvel, the microprocessor.

There is some dispute as to which company invented the microprocessor, and we’ll talk about that further down. But who invented the first commercially available microprocessor? That honor goes to Intel for the 4004.

Path To The 4004

Busicom calculator motherboard based on 4004 (center) and the calculator (right)
Busicom calculator motherboard based on 4004 (center) and the calculator (right)

We pick up the tale with Robert Noyce, who had co-invented the IC while at Fairchild Semiconductor. In July 1968 he left Fairchild to co-found Intel for the purpose of manufacturing semiconductor memory chips.

While Intel was still a new startup living off of their initial $3 million in financing, and before they had a semiconductor memory product, as many start-ups do to survive they took on custom work. In April 1969, Japanese company Busicom hired them to do LSI (Large-Scale Integration) work for a family of calculators.

Busicom’s design, consisting of twelve interlinked chips, was considered a complicated one. For example, it included shift-register memory, a serial type of memory which complicates the control logic. It also used Binary Coded Decimal (BCD) arithmetic. Marcian Edward Hoff Jr — known as “Ted”, head of the Intel’s Application Research Department, felt that the design was even more complicated than a general purpose computer like the PDP-8, which had a fairly simple architecture. He felt they may not be able to meet the cost targets and so Noyce gave Hoff the go-ahead to look for ways to simplify it.

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Bespoke Processors Might Soon Power Your Artisanal Devices

Modern microprocessors are a marvel of technological progress and engineering. At less than a dollar per unit, even the cheapest microprocessors on the market are orders of magnitude more powerful than their ancestors. The first commercially available single-chip processor, the Intel 4004, cost roughly $25 (in today’s dollars) when it was introduced in 1971.

The 4-bit 4004 clocked in at 740 kHz — paltry by today’s standards, but quite impressive at the time. However, what was remarkable about the 4004 was the way it shifted computer design architecture practically overnight. Previously, multiple chips were used for processing and were selected to just meet the needs of the application. Considering the cost of components at the time, it would have been impractical to use more than was needed.

That all changed with the new era ushered in by general purpose processors like the 4004. Suddenly it was more cost-effective to just grab a processor of the shelf than to design and manufacture a custom one – even if that processor was overpowered for the task. That trend has continued (and has been amplified) to this day. Your microwave probably only uses a fraction of its processing power, because using a $0.50 processor is cheaper than designing (and manufacturing) one tailored to the microwave’s actual needs.

Anyone who has ever worked in manufacturing, or who has dealt with manufacturers, knows this comes down to unit cost. Because companies like Texas Instruments makes millions of processors, they’re very inexpensive per unit. Mass production is the primary driving force in affordability. But, what if it didn’t have to be?

Professors [Rakesh Kumar] and [John Sartori], along with their students, are experimenting with bespoke processor designs that aim to cut out the unused portions of modern processors. They’ve found that in many applications, less than half the logic gates of the processor are actually being used. Removing these reduces the size and power consumption of the processor, and therefore the final size and power requirements of the device itself.

Of course, that question of cost comes back into play. Is a smaller and more efficient processor worth it if it ends up costing more? For most manufacturers of devices today, the answer is almost certainly no. There aren’t many times when those factors are more important than cost. But, with modern techniques for printing electronics, they think it might be feasible in the near future. Soon, we might be looking at custom processors that resemble the early days of computer design.

 

An Intel 8085 Microprocessor Trainer

The Intel 8085 microprocessor was introduced 40 years back, and along with its contemporaries — the Z80 and the 6502 — is pretty much a dinosaur in terms of microprocessor history. But that doesn’t stop it from still being included in the syllabus for computer engineering students in many parts of the world. The reason why a 40 year old microprocessor is still covered in computer architecture text books instead of computer history is a bit convoluted. But there’s a whole industry that thrives on the requirements of college laboratories and students requiring “8085 Microprocessor Training Kits”. [TisteAndii] just finished college in Nigeria, where these kits are not locally built and need to be imported, usually costing well over a 100 dollars.

Which is why his final year project was a low cost Intel 8085 Microprocessor Trainer. It’s a minimalist design with some basic read/write memory, program execution and register inspection, with no provision for single stepping or interrupts yet. The monitor program isn’t loaded in an EEPROM. Instead, a PIC18 is used and connected to the 8085 address, data and control pins. This makes it easier to write a monitor program in C instead of assembly. And allows use of a 1.8″ LCD with SPI interface instead of the more usual 7-segment displays used for these kind of kits. [TisteAndii] built a 6×4 keyboard for input, but couldn’t solve debounce issues and finally settled on a 5×4 membrane keypad.

Being a rookie, he ended up with a major flaw in his board layout — he missed connecting the SRAM and the PPI devices to the data bus. A bunch of jumper links seemed to solve the issue, but it wasn’t perfect. This, and a few other problems gave him a lot of grief, but towards the end, it all worked, almost. Most importantly, his BoM cost of about $35 makes it significantly cheaper compared to the commercial units available in Nigeria.

While some hackers may consider this a trivial project, it solves a local problem and we hope the next iteration of the design improves the kit and makes it more accessible.

The Surprising Story Of The First Microprocessors

If you maintain an interest in vintage computers, you may well know something of the early history of the microprocessor, how Intel’s 4-bit 4004, intended for a desktop calculator, was the first to be developed, and the follow-up 8008 was the first 8-bit device. We tend to like simple stories when it comes to history, and inventions like this are always conveniently packaged for posterity as one-off events.

In fact the story of the development of the first microprocessors is a much more convoluted one than it might appear, with several different companies concurrently at the forefront of developments. A fascinating recent IEEE Spectrum piece from [Ken Shirriff] investigates this period in microprocessor design, and presents the surprising conclusion that Texas Instruments may deserve the crown of having created the first 8-bit device, dislodging the 8008 from its pedestal. Continue reading “The Surprising Story Of The First Microprocessors”

Megaprocessor is a Macro Microprocessor

If we have to make a list of Projects that are insane and awesome at the same time, this would probably be among the top three right up there. For the past few years, [James Newman] has been busy building Megaprocessor – a huge micro-processor made out of transistors and LED’s, thousands of ’em. “I started by wanting to learn about transistors. Things got out of hand.” And quite appropriately, he’s based out of Cambridge – the “City of perspiring dreams“. The Why part is pretty simple – because he can. We posted about his build as recently as 10 months back, but he’s made a ton of progress since then and an update seemed in order.

megaprocessor_04How big is it ? For starters, the 8-bit adder module is about 300mm (a foot) long – and he’s using five of them. When fully complete, it will stretch 14m wide and stand 2m tall, filling a 30 sq.m room, consisting of seven individual frames that form the parts of the Megaprocessor.

The original plan was for nine frames but he’s managed to squeeze all parts in to seven, building three last year and adding the other four since then. Assembling the individual boards (gates), putting them together to form modules, then fitting it all on to the frames and putting in almost 10kms of cabling is a slow, painstaking job, but he’s been on fire last few months. He has managed to test and integrate the racks shown here and even run some code.

The Megaprocessor has a 16-bit architecture, seven registers, 256bytes of RAM and a questionable amount of PROM (depending on his soldering endurance, he says). It sips 500W, most of it going to light up all the LED’s. He guesses it weighs about half a ton. The processor uses up 15,300 transistors and 8,500 LED’s, while the RAM has 27,000 transistors and 2,048 LED’s. That puts it somewhere between the 8086 and the 68000 microprocessors in terms of number of transistors. He recently got around to calculating the money he’s spent on this to date, and it is notching up over 40,000 Quid (almost $60,000 USD)!  You can read a lot of other interesting statistics on the Cost and Materials page.

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Code Craft: Subtle Interrupt Problems Stack Up

[Elliot Williams’] column, Embed with Elliot, just did a great series on interrupts. It came in three parts, illustrating the Good, the Bad, and the Ugly of using interrupts on embedded systems. More than a few memories floated by while reading it. Some pretty painful because debugging interrupt problems can be a nightmare.

One of the things I’ve learned to watch out for over the years is the subtlety of stack based languages, like C/C++, which can ensnare the unwary. This problem has to do with the corruption of arrays of values on a stack during interrupt handling. The fix for this problem points up another one often used by black hats to gain access to systems.

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Non-Arduino powered by a piece of Computing history

Sometimes it is a blessing to have some spare time on your hands, specially if you are a hacker with lots of ideas and skill to bring them to life. [Matt] was lucky enough to have all of that and recently completed an ambitious project 8 months in the making – a Non-Arduino powered by the giant of computing history – Intel’s 8086 processor. Luckily, [Matt] provides a link to describe what Non-Arduino actually means; it’s a board that is shield-compatible, but not Arduino IDE compatible.

He was driven by a desire to build a single board computer in the old style, specifically, one with a traditional local bus. In the early days, a System Development Kit for Intel’s emerging range of  microprocessors would have involved a fair bit of discrete hardware, and software tools which were not all too easy to use.

Back in his den, [Matt] was grappling with his own set of challenges. The 8086 is a microprocessor, not a microcontroller like the AVR, so the software side of things are quite different. He quickly found himself locking horns with complex concepts such as assembly bootstrapping routines, linker scripts, code relocation, memory maps, vectors and so on. The hardware side of things was also difficult. But his goal was learning so he did not take any short cuts along the way.

[Matt] documented his project in detail, listing out the various microprocessors that run on his 8OD board, describing the software that makes it all run, linking to the schematics and source code. There’s also an interesting section on running Soviet era (USSR) microprocessor clones on the 8OD. He is still contemplating if it is worthwhile building this board in quantities, considering it uses some not so easy to source parts. If you are interested in contributing to the project, you could get lucky. [Matt] has a few spares of the prototypes which he is willing to loan out to anyone who can can convince him that they could add some value to the project.

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