The Processor: A Small Set of Actions
Memory just lies there — numbered cells holding numbers. Something has to act: read, change, decide. That something is the processor, the second part of our idealized machine, and this lesson states the second great assumption of the course: the processor is astonishingly simple.
Start with the question
Your machine translates languages, renders worlds, recognizes faces. So the processor inside must be terribly sophisticated — surely it has a "translate" ability, a "draw" ability, a "recognize" ability somewhere in its depths?
It has none of them. The honest answer — and the second assumption of our course — is that the processor can do only a handful of tiny things. Everything impressive you have ever seen a computer do is built, without exception, out of these few bricks, repeated billions of times per second.
The complete set of actions
Here is everything our processor can do. Not the highlights — everything:
| Action | What it does |
|---|---|
| Read | Given an address, fetch the number lying in that cell |
| Write | Given an address and a number, put that number into that cell (replacing what was there) |
| Arithmetic | Add or subtract two numbers; compare two numbers (which is larger, are they equal) |
| Choose what's next | Select which action to perform next — the quiet one on this list, and the future source of all "intelligence" |