1972: When scientific calculators truly went low power

Dave Cochran recently wrote about his long engineering career at Hewlett-Packard on the www.hpmemory.org Web site. Who? What Web site? Well, the Web site is an amazing living museum that’s a tribute to Bill and Dave’s HP. And Dave Cochran is likely one of the most important people you’ve never heard about in the annals of low-power design. He spent 25 years at HP, starting as a part-time test technician in 1956 and departing as a celebrated HP engineer in 1981.

Between those two years, Cochran worked on a huge number of projects including the HP 204B audio oscillator where he used transistors and a hugely ingenious double-spiral-cam potentiometer actuator to design the famous tungsten light bulb out of Bill Hewlett’s original audio oscillator design. (That double-cam actuator makes a linear pot do unnatural things and you need to see the short, 3-second video to believe it!) But it’s what he did in the 1960s and 1970s that make him the topic of this particular blog post.

Cochran was working at HP Labs when Malcolm McMillan and Tom Osborne dropped by with two very different calculator prototypes. It was the legendary Barney Oliver, Grand Wizard of HP Labs who conjured the idea of merging these two very different machines into one massively powerful scientific calculator. McMillan’s design—called Athena—could perform transcendentals using Jack Volder’s CORDIC algorithms but it had a fixed-point architecture so it was not deemed accurate enough for repeated engineering calculations. Osborne’s design was barely more than a simple 4-banger calculator but it had a really elegant, floating-point hardware design based on the 1960s version of a VLIW processor.

Cochran got the job of trying to come up with a way to unify the two architectures. He writes “I was looking at Osborne’s architecture and trying to figure out what an algorithm was. I even flew down to Southern California to talk with Jack Volder who had developed the CORDIC  transcendental functions used in the Athena machine and talked to him for about an hour. He referred me to the original papers by Meggitt where he’d gotten the pseudo division, pseudo multiplication generalized functions.

My job was to determine how many digits and what the operation time was required; what the architecture had to be; how many registers did we need, clock speed, etc? Other people were coming back with their inputs on cathode ray tube display, keyboards [and so on]. Should we use transistors or small-scale integration? There was no large-scale integration, but there was medium-scale integration, MSI which meant maybe 10 transistors in a chip.”

From Cochran’s architectural contributions, plus substantial work from other engineers in HP Labs and Tom Osborne (who remained an HP consultant for many more years), HP introduced the HP 9100 Scientific Calculator in late 1968. It’s a marvelous machine and it was a real design breakthrough for its day. It also weighed 40 pounds and drew 70 Watts out of a wall socket.

Now 70W isn’t all that much compared to the amount of electrical power you’d need to replicate the HP 9100’s computational abilities with a minicomputer or a mainframe, so you could consider this a lower-power design for its day. But it’s what happened next that really takes us to the domain of miraculously low power.

Cochran writes: “As soon as the 9100 started showing success in the market place Hewlett started to bug me personally. I know he also talked to Tom Osborne about it, what do you think, and so on. But he would come into the lab and he’d look for me and he’d say, ‘Hey, how are you coming with putting the 9100 in my shirt pocket?’ He said, ‘I want all that computational power in my shirt pocket.’”

OK. From 40 pounds and 70W to something that runs off batteries and fits in your shirt pocket. Now that’s a stretch. Oh, and one thing I forgot to mention. The HP 9100 calculator design had exactly one integrated circuit in it. That IC was used in the magnetic card reader. Osborne didn’t like the primitive ICs offered at the time. He didn’t design the card reader but the rest of the machine was implemented with discrete transistors, magnetic-core RAM, rope memory (go look that one up), and a large capacitive ROM fabricated from a 16-layer printed-circuit board. None of that technology was headed for a shirt pocket. Not in this universe.

Cochran then writes about his shirt-pocket epiphany: “Tom Whitney and I went down to Fairchild Semiconductor on Ellis Street, Mountain View, and they wanted to show us a calculator architecture that they were planning to provide to various companies that wanted to build calculators and semiconductors. So we went down to look at it. And I looked at it, and oh, this could do the algorithms. See, I knew. By this time, I had already fit the algorithms into a small-scale integrated machine, the 9100. So I knew exactly what architecture I needed, the capabilities of the architecture. I didn’t know what it was going to look like, but I knew what its capabilities had to be.

It was I think September of 1970; I saw a design that was different than anything else. It was not your classic computer architecture as taught at the universities. It was all shift register. It was designed for the technology at the time. When talking to the people at Fairchild I meet a fellow, Rich Whicker, who later came to work at HP. I said, “God, this design, did you think of this?” He says, “No. We got it from Sweda, the cash register company.” Sweda at the time was trying to make an electronic cash register or Point-of-Sale products and they were using shift registers.

Shift registers were the densest form of integration of integrated circuits at the time; you had to keep the clock moving and so on. It had no static memory. So here was a design using shift registers a 20-digit chipset that could satisfy anybody making a four-function machine. Add, subtract, multiply, and divide. It could give you the numbers as big as most people wanted, but it was all fixed point. 20 digits should be more than enough for anybody. You could have the decimal point anywhere in that stream.

I got really cranked up about seeing that architecture at Fairchild, I got very excited. And I’m whispering in Tom Whitney’s ear, ‘God, this is great.’ And I’m trying not to be too excited while I’m there. When we drove away from there and, I said, ‘God, that’s exactly—you know, I can tweak that architecture just a little bit. We don’t need the full 20 digits, we can do this and this and this. And gosh, yes, I can do it, I can do it, I can do it.’”

And that’s when the HP 35 Pocket Scientific Calculator crossed over from the realm of the impossible to the realm of the possible. When David Cochran thought that it could. Two years later, in 1972, it became a reality. A pocket scientific calculator that ran on three NiCd batteries in a pack. The rest, as they say, is history.

Be sure to read the whole story at http://www.hpmemory.org/timeline/dave_cochran/a_quarter_century_at_hp_00.htm#chapter_08.

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