Step 82: Improve Computer Organization Lectures

A while back I mentioned that, for the first time, I included in CS1 a series of classes introducing students to other topics in computer science. It was a series of eight lectures, which covered in order:

  • Memory Layout, starting with the binary representations of numbers and strings, to the idea of pointers and the idea of treating programs as data.
  • Recursion, mostly the ideas of base case and recursive case, with a simple application of printing the contents of nested directories.
  • Artificial Intelligence, specifically problem solving as search and a very high-level overview of machine learning
  • Parsing, although the class turned into me using recursion to build a basic interpreter for arithmetic variables and expressions.
  • The Internet, mostly the idea of networks, DNS, and routing, with a little DDOS thrown in.
  • Security and Privacy, mostly best practices for personal digital security, but also some implications for privacy in the age of AI.
  • Computer Architecture, which includes the CPU, memory hierarchy, and OS, with a little bit of digital circuitry.
  • Assembly, which is exactly that, using this excellent 8-bit simulator.

This culminated in an essay where students have to explain how a computer works to the layperson. The overall idea was influenced by courses like Harvey Mudd’s CS 5, which explicitly allows students to sample upper-level courses. Michigan’s EECS 183 used to do something similar when I taught it two years ago, although it looks like they have since shrunk the number of classes reserved for these grab-bag topics. Finally, this sequence also borrows from ideas like From NAND to Tetris, although I’m going top-down instead of bottom-up with interwoven additional topics (and I’ve clearly thought through the sequence less than authors of the book).

Individually, teaching these topics did not strike me as problematic. I particularly enjoyed the memory and assembly lectures, not only because they were mind-blowing for students, but because it was material I haven’t used myself in a long time. The most difficult topics for students were recursion and parsing. For the latter, I was surprised by the lack of articles that explained in simple terms why recursion was necessary. Even now, I find myself unable to adequately explain why ordinary loops are insufficient, at least not without talk about stacks and trees. The remaining topics were ones that I have taught before, either in previous semesters of this course (the Internet lecture) or in cognitive science (AI), and all went passingly.

As a whole, however, this sequence of classes need rethinking. Even before the teaching evaluations, some students already told me that I could have better integrated the topics. It’s true that, without additional information, it’s unclear why we need CPUs and RAM and all the other components of a computer, and how an executable fits into it all. Missing the big picture also made the cumulative essay somewhat obtuse, which was corroborated in an evaluation comment: “I felt that I had very little insight to add to the paper besides technical information that I pulled from other sources.” While some students did manage to combine the topics into a coherent narrative of how code works, many other essays lacked transitions between descriptions of each system.

My takeaway here is that this sequence is too ambitious, even at the mile-high view of each topic. It was a useful exercise to see where the limits of the course are, but I think one student had the right idea: “I would prefer that instead of spending the last month learning other things about computers, to instead spread out the computer science material so it can be taught at a slower pace.” Some students did enjoy the breadth of topics, so my plan for the future is to reduce the number of grab-bag classes, but allow students to select the topics they are most interested in (but perhaps requiring the one on memory). I suspect the parsing lecture will never be chosen, but since I’m not sure how much students got out this semester anyway, I don’t see it as a huge loss.

Step 82: Improve Computer Organization Lectures

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