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Notes As Cache

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Notes As Cache

I want to draw an analogy between note-taking, memory and learning, on the one hand, and the various tiers of storage on a computer on the other.

Tiers of Computer Storage

A CPU works primarily, or sometimes entirely, with values stored in internal registers. (An x86_64 CPU allows you to specify memory locations as operands, whereas a RISC CPU requires that everything be loaded to registers before being operated on, and stored back to memory from registers when done.)

Now compared to the speed of the CPU, main memory is very slow. And then, compared to main memory, storage on a local device like a disk or SSD is many orders of magnitude slower still. And storage in the cloud is slower still. And offline storage has as much latency as it takes you to dig that old hard drive out of the cupboard and plug it in.

Between main memory and the CPU there are then a number of levels of cache. The smallest, fastest, and closest to the CPU is the level 1 cache, perhaps only 16KB, possibly split into two separate caches, one for data and one for memory. Then there are often two more levels of cache, if not three. The second level cache tends to be larger, slower, but each core in the CPU has its own level 2 cache. Then there is often a third level cache, larger and slower again, that is shared by all the cores on a CPU package.

The idea is this: what the CPU is working on is stored in internal registers (even if an instruction references a location in RAM, behind the scenes the CPU will fetch that value to an internal register before operating on it). What isn't in the internal registers must be fetched from RAM. And this is where caches come in: often you want to reload the same piece of data many times. So the cache provides a way to recall commonly used bits of data more quickly, so that the CPU needs only fetch it from one of the caches, preferably the level 1 cache.

Notes As Cache

When it comes to learning, researching things online or reading them in books is slow. It may take days and many efforts to find the bit of information you are after. You may need to read half of a 1000-page textbook until you've found what you're after. And while sometimes necessary, you don't want to do this any more than you need to: research soaks up time as a sponge soaks up water.

So when you learn something, you want a means to not have to research it again in future. This is where notes come in. And notes come in in a number of ways:

  1. If you find something in a textbook, note down what you found and where it is in the textbook and which textbook it is.
  2. If you find something in a textbook, write a summary in your notes, hopefully enough so that, in the near future, you can recall what you need by only reading your notes.
  3. For things you commonly dig out of your notes, write separate, condensed notes which summarise those things: so that they are easier to find (since your collection of condensed notes is smaller and takes less time to read). For things you do commonly, some things will be burned into your memory, and you only need notes to remind you of the bits you don't remember.
  4. If you regularly practise re-reading things from notes, you become better at doing this, and you learn where your notes work well, and where they don't. Where you notes don't work well, it pays to spend time to improve how you write things down.
  5. For things you regularly fetch from your notes, it is worth spending time intensively practising and revising so that much of it is transferred into your memory: you practise scales and chords so that you know them without having to think about them, so practise other common patterns in the same way.

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