How your computer works.

Your program is really millions of tiny instructions, and the CPU fetches, decodes and executes them billions of times a second. See what physically happens when a single line of your code runs — the fetch-decode-execute heartbeat under everything.

Type 0.1 + 0.2 into any language and you get 0.30000000000000004. It's not a bug — computers store numbers in binary with finite bits, and most decimals simply don't have an exact binary form. Once you see why, floating point stops surprising you.

One encoding holds every language on Earth — emoji, Arabic, Chinese — while staying perfectly backward-compatible with plain old ASCII. UTF-8's variable-length trick is one of computing's quiet masterpieces, and it explains a lot of "why is my text garbled" bugs.

A segfault is your program reaching for memory it doesn't own, and the operating system slamming the door before it can do damage. Understand virtual memory — the illusion that every process has the whole machine to itself — and the segfault stops being scary.

Languages that don't make you free memory by hand still have to reclaim it somehow — figuring out what's no longer reachable and cleaning it up, ideally without freezing your program. That's garbage collection, and it's a beautiful trade-off between throughput and pause time.

How does an SSD keep your data with the power off and no moving parts? Flash memory traps electrons in microscopic cells that hold their charge for years — and wears out a tiny bit with every write, which is why wear-leveling exists.

ZIP makes a file smaller and then restores it byte-for-byte — no data lost. The trick is finding redundancy (repeated patterns, common symbols) and encoding it more efficiently. It's the same core idea from text files to the compression baked into every network protocol.

How do two strangers agree on a secret while everyone is listening? Public-key cryptography gives everyone a public key to encrypt with and keeps a private key that alone can decrypt — the math trick that makes HTTPS, signatures and secure messaging possible.

Light is fast, but it is not instant — and across a chip, a data center, or a planet, that finite speed becomes the hard floor on latency that no clever code can beat. It's why memory hierarchies exist and why a round-trip to another continent will always cost you.

The finale ties the layers together: a container isn't a tiny virtual machine at all — it's a normal process the kernel has fenced off with namespaces and cgroups so it believes it has the whole machine to itself. Once you see that, Docker stops being magic.