Unlike Magnets, Computers can be Explained¶

The Bit¶

Make a One-bit memory.

I’m seriously here, your first lesson is to make a device, no matter how simple, that stores one bit. It can be:

• A coin, flip heads for 1, tails for 0.
• A match, horizontal or vertical, head up or head down...
• A short length of string, knotted for 0, untied for 1.
• A rubber-band, knotted for 1, unknotted for 0.
• A business card, horiz. v. vert., front v. back, bent v. straightened.
• Even a light switch from a hardware store.

Literally any binary “storage” scheme could be accepted, as long as the student truly gets the arbitrary mapping from a physical phenomenon to a binary digit. I am convinced that doing this physically, with real world objects, is crucial. Take your time here, don’t rush. The binary digit is a deep sucker, it just seems so plain on first brush. (Hint: What is the least “stuff” you need to make a bit? Sample rate and resolution... What the heck “is” a bit anyway? You can’t carry it, but you can transmit it, what’s up with that? And you can duplicate it? Huh?)

Line up eight of them. Make a byte.¶

Once you’ve made a bit-store, the next lesson involves lining them up and flipping them on and off.

Count the states, number them, talk about:

• n-to-the-power-of-two
• Grey Codes
• I Ching
• distinguishable states
• Boolean logic
• all the deep meanings already present in more-than-one-bit-ness. (Twenty Questions!)

Make concrete the Octet, aka Byte, mention ASCII, signed and unsigned “short” ints, Unicode and encodings (to bytes) and thence sixteen-bit and larger words.

Stack up a bunch of bytes. Make RAM.¶

• Take some bytes, at least a dozen, and stack them in a column. Count the bytes, introduce the count as naming or indexing the bytes, call it RAM.
• Show how a few consecutive bytes of RAM can store a string of ASCII codes.
• Do a couple of math problems using two adjacent bytes as (binary) operands and another byte to store the result.
• Move a couple of bytes from one area in the RAM to another.

Addresses, numbers, operations, naming. (microcode)¶

Wonder at the beauty and greatness of what we’ve done so far. We mapped binary digits (bits) to real world phenomenon. We used a simple coding system, algebra in base two, to encode the integers into bit patterns. We created a “strip” or “column” of bits, organized in eight-bit-wide words called bytes or octets, and then numbered those, counted them to name them, and began to use this abacus-like crude machine of ours to perform simple operations like math, logic, and “string” manipulation.

The Power of Naming¶

Start to make the steps used to perform these operations more concrete. Use index cards or something and list out the various steps you take in performing a few simple math/logic problems and stuff.

Do the counting-to-name-things trick yet again to enumerate the “microcode” you’ve developed, and lay in a simple program using it.

Act out the Fetch-Execute cycle and let people get used to the idea of how simple it is. Maybe even assign each instruction of microcode to a different person and have the class cooperatively act out the solving of a simple math problem or two according to an in-memory machine language program. (That will prove viscerally that you don’t need a brain or mind to “be” a computer. Put another way, some classes of mental operation can be automated, carried out by machine.)

(You would also introduce the idea that RAM can be a lot larger than just a dozen bytes or so, and likely mention registers too.)

Parsing, Grammar, Compiling.¶

Ahem, some about that and the Meta-Compiler...