Logic Lessons That Last Generations

Editor's Notes

• #2: This is the story of a book. To paraphrase Douglas Adams, it’s the story of “a wholly remarkable book.” A book that turned a writer from the 1960s into a time traveller, an old engineer into a teacher, and a young boy into an engineer. A book with lessons for all of us, should we choose to listen, about how we explain, how we document, and how we build a legacy, both individually and as a programming community.\n
• #3: The story of that wonderful, beautiful Thursday, (channeling Adams again) “the story of its extraordinary consequences, and the story of how those consequences are inextricably intertwined with this remarkable book begins very simply. It begins with a house.”\n
• #4: Before we get to that, do any of you have an important person in your lives who had a lot to do with your getting into technology? A parent, teacher, or friend? What memories do you have of your path to technology?\n
• #5: This my grandparents’ house in East Texas where my family would descend several times a year to ride horses, chase dogs around, and so on.\n
• #6: That’s me among all my cousins. One of my favorite things to do during these visits was watch my grandfather work in his garage laboratory.\n
• #7: By day, my grandfather was an engineer. By night, he restored and operated radios. To his friends, he was Pete.\n
• #8: To the FCC, he was W5YNI.\n
• #9: To me, he was Grampy. I don’t know why he put up with my hanging around in his lab. Perhaps he saw my interest in engineering even before I did.\n
• #10: Rands continues: “When they were six, their Dad handed them two boards, a nail, and a hammer and they started whacking. BLAM BLAM BLAM. Even with the nail awkwardly bent in half, the wood was suddenly and magically bound together: a thing was built. At that moment, this junior engineer’s brain excreted a chemical that instantly convinced them of the disproportionate value of this construction. This is the best wood thing in the world because I built it. And then they looked up from their creation and pleaded, ‘Dad, I really need more nails.’”\n
• #11: One day, Grampy presented me with a plain black three-ring binder. It looked ancient. It had long-abandoned spider nests in the binding. It was dusty and greasy.\n\n
• #12: When I opened it, I saw yellowed pages bearing the words, “Binary Logic,” by William S. Bennett.\n
• #13: The next page confronted me with a simple definition...\n
• #14: ...followed by a simple puzzle. I’m sure you know the answer to this question. But just for fun, let’s follow one of the incorrect answers.\n
• #15: The book sets us gently back on course,....\n
• #16: ...and we eventually find the correct solution.\n
• #17: Immediately, we’re asked to apply what we’ve learned. Which circuit implements the AND gate we’ve just read about?\n
• #18: If Markus Roberts is in the audience, he will cite DeMorgan’s Theorem and point out that the answer depends on whether you count a lit light bulb as on or off.\n
• #19: The book continues in the same style from there. Let’s take a step back for a sec. What on earth is this thing?\n
• #20: The page footer gives us a clue. This was a series of columns that ran in Product Engineering magazine from 1962-3, and again in 1965.\n
• #21: As near as I can tell, Product Engineering ran from the ‘40s to the ‘60s. It seemed to be kind of like Popular Mechanics for design engineers. Geek-speak meets “the flying car of tomorrow.”\n
• #22: This particular column on binary logic was basically a Choose Your Own Adventure book for grown-ups. The editor referred to it as a “teaching machine” or “scrambled book.”\n
• #23: Before we get too excited about the possibilities, observe that the phrase “teaching machine” reminds us of interfaces that use the customer as a peripheral. As we’ll see, this book demands much more active involvement than that.\n
• #24: Frank Hall, the editor of the magazine, cited research that the “scrambled book” teaching method lets diverse audiences gain the same skill set at their own pace, and that reinforcement and feedback are crucial parts of the process. \n
• #25: This emphasis on rapid feedback reminds me of Bret Victor’s excellent talk “Inventing on Principle,” in which he builds extremely interactive user interfaces in the service of a larger point about having a life's mission.\n
• #26: Let’s go back and look at the puzzle we just solved, and see the way Bennett is already teaching us not just how to understand binary logic, but also how to teach. First, he starts with one easy achievement—an early success to hook the reader.\n
• #27: He leaves easy navigation markers: we always know where we came from and where to go if we get lost.\n
• #28: So, these are the first two lessons from diving into this work: get your reader to an early success, and don’t punish them for veering off the path.\n
• #29: So, these are the first two lessons from diving into this work: get your reader to an early success, and don’t punish them for veering off the path.\n
• #30: Incidentally, this notion of setting up early obstacles that are just the right difficulty level is related to the Dreyfus model cited by just about everyone these days.\n
• #31: In this model, you adapt your teaching style to the audience. This implies that the tips we’re talking about today are not universal. Bennett’s audience was engineers who knew other disciplines, but were novices at binary logic.\n
• #32: The next thing the book does is present us with an analogy to familiar items.\n
• #33: Several analogies, in fact, drawing first from simple electrical and mechanical devices.\n
• #34: In one clever setup, the author even makes his hypothetical mechanical device physically resemble the old schematic symbol for an OR gate.\n
• #35: The devices get more elaborate; here’s another OR gate. Since this device is a series of tubes, it may be a mechanical precursor to the internet. ;-)\n
• #36: The book branches out into other engineering disciplines, even using optical elements in some examples.\n
• #37: In other words, Bennett is meeting the reader on their terms.\n
• #38: Let’s look through some more steps in the process.\n
• #39: After we’ve mastered the basics, Bennett introduces some humor. This went over my head at the time; I thought he was saying the measurements were intolerable!\n
• #40: The schematic resembles that famous Usenet gag about a universal flowchart for diagnosing engineering problems.\n
• #41: Going for the cheap laugh is of course fine; just do so in moderation.\n
• #42: Here, Bennett introduces what he says is a labor-saving device: algebraic notation for simplifying logic diagrams.\n
• #43: But it turns out it was just a backdoor way of preparing us for DeMorgan’s theorem...\n
• #44: ...which basically says you can reverse the meanings of AND, OR, and NOT in a circuit and still get the same result. This is a huge deal in logic design; you can build an entire design out of one kind of component.\n
• #45: This teaching by misdirection was dubbed a “head fake” by Randy Pausch,...\n
• #46: ...in his famous Last Lecture.\n
• #47: Next, Bennett has us putting building blocks together in bigger combinations. Consider this circuit that folds in on itself.\n
• #48: As you toggle one of the inputs at the bottom,...\n
• #49: ...both outputs at the top change state and stay in their new configuration.\n
• #50: This kind of circuit is known as a flip-flop. It’s the foundation of electronic memory.\n
• #51: If you don’t want the inconvenience of two inputs, you can combine them into a single “toggle” input.\n
• #52: Once you have one-bit memory cells, you can assemble them into four-bit numbers and compare them.\n
• #53: You can also chain them one to the next, building a circuit that can count numbers.\n
• #54: These are the building blocks of a computer! By the end of the course, you’ve essentially seen the most important pieces of a CPU.\n
• #55: Bennett has brought us from “this is an AND” to “go design your own computer.” He has given us the power to create value.\n
• #56: Then, just to drive the point home, he spends another advanced lesson showing us more analogies. Here’s a flip-flop made of pulleys.\n
• #57: Here’s another flip-flop; this one’s made of moving air! The research to create thin sandwiches of transparent material was new at the time. Bennett was using his column to give us sneak peeks at emerging technologies.\n
• #58: Here’s a NOR gate made of moving fluid...\n
• #59: ...and an AND gate. He has deliberately chosen these layouts...\n
• #60: ...to prepare us for the actual implementation of the logic gates in silicon.\n
• #61: These analogies started out as a warm, fuzzy way to introduce the core teaching concepts, and now they’re being used to go the opposite direction: to branch out into new territories.\n
• #62: The last part of Bennett’s course is the final exam.\n
• #63: If you send in your correct answers and 50 cents handling, you get your very own diploma.\n
• #64: Remind you of anything?\n
• #65: We talk a good (ahem) game about gamification these days, but Bennett beat us to the punch by about 40 years.\n
• #66: By engaging us in this quest, Bennett has basically tricked us into designing a computer. We’ve fought our way through obstacle after obstacle, including a final boss.\n
• #67: This whole journey through the book, culminating in slaying the final dragon and collecting riches, supports the idea of the reader as a hero.\n
• #68: The Pragmatic Programmers talk about this a lot. In fact, the Author’s Guide they distribute to everyone who writes for them contains a whole chapter on the idea.\n
• #69: And I suppose now’s as good a time as any to tell you I’m writing another book for them. This one’s on Cucumber. I get to sleep at night by telling myself there’s a connection to this talk in there somewhere—indeed, good tests can tell a story.\n
• #70: As we move into the final phase of this talk, I’d like to talk about a couple of the many questions I’ve asked about Bennett’s remarkable book.\n
• #71: First, as delightful as it is that this book is still engaging and relevant, how to we preserve it?\n
• #72: Indeed, how do we preserve anything?\n
• #73: One answer is translating into other media. McGraw Hill did republish the work in paperback form in the ‘70s. I’ve written them to ask permission to go further, and translate the work into hypertext.\n
• #74: Perhaps an even better venue would be an interactive story; for more on how to build those, see Bart’s talk on Thursday at 10:00.\n
• #75: The thing about casting things as stories like this is that they have as big of a beneficial impact on the storyteller and the material itself as they do on the listener.\n
• #76: The other big question is, how did Bennett manage to create this enduring work in the first place? Did he even know how significant his creation would be?\n
• #77: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #78: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #79: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #80: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #81: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #82: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #83: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #84: That brings us back around to the lessons we’ve gleaned from looking at this work.\n
• #85: Speaking of the hero’s journey, here’s a eulogy written by one of my Grampy’s fans. I found it among the family photos I was scouring for material for this talk.\n
• #86: In particular, see how Grampy taught more people than just me. His passion for engineering is still rippling throughout the universe.\n
• #87: I don’t think Grampy was worried about trying to preserve his legacy. I think he was just doing what he loved, and encouraging others to do the same.\n
• #88: This means we don’t have to sweat this, either. Any one in this room could build something that people are still talking about generations from now. Any one of you could teach one person a skill and see that knowledge spread to thousands. I am standing in a room full of conquerors and heroes, with any luck I’ll be around long enough to see the impact of your deeds far and wide. Cheers.\n