There are exactlyfour problemsin computing.
Every hard problem in computing is one of four problems — often two or three at once.
One sketch, sixteen examples.
Each column is a primitive. Each cell is a famous instance of it. Note that zero-knowledge appears twice — it does two jobs at once.
What each primitive really is.
Compression
Compression is the conversion of mass into representation. A model is a compressed corpus. A proof is a compressed argument. A hologram is a compressed scene. Every act of cognition is compression: a billion sensations become one thought.
Encoding — the original compression
Take one alphabet, rewrite it in another that's denser, more error-tolerant, or shaped to the channel. Huffman, ASCII, UTF-8, JPEG, AAC, H.264. Encoding is where compression first becomes engineering.
GPT — compressing the corpus
A trillion documents become a few hundred gigabytes of weights. Decompression is not retrieval; it is sampling. The model is lossy in detail, lossless in style, and learned how to be both.
Zero-knowledge proof — compressing an argument
A million-step computation becomes a few hundred bytes of proof — verifiable in milliseconds, revealing nothing more than that it ran. Compression and privacy in one stroke.
Holography — compressing a scene
An entire light-field encoded as a flat interference pattern, decodable from any angle. The original 3D-into-2D, with parallax recovered on read.
Ordering
Ordering is the conversion of concurrence into sequence. Which transaction came first? Which fact matters most? Which item to show? Civilization runs on agreed-on orderings — and most civilizational arguments are over them.
Transaction ordering — the consensus problem
Many parties broadcast actions; the system must produce one canonical sequence that all of them accept. This is what a blockchain actually is. Money is an opinion about ordering.
Event ordering — what came before what
Lamport clocks. Vector timestamps. Causal graphs. Distributed systems can't observe absolute time, so they construct partial orders out of who-saw-whom. Time is something a system has to earn.
Search — ordering by relevance
PageRank turned the web into a directed graph and asked: which page does everyone else point to? Search engines don't find pages. They sort them.
Recommenders — ordering by you
Same problem as search, with the query replaced by an inferred you. The feed is a stream-shaped ranking. Attention has become a sorting workload.
Concurrency
Concurrency is the art of letting many do work without stepping on each other. Hardware parallelism, distributed protocols, sharding, edges — all variations of "how do n things share one world?". The hard part is not speed. It is consistency under load.
Parallelism — one machine, many threads
GPUs, SIMD, vectorisation, async runtimes. Within a single box, find work that doesn't depend on itself and do it all at once. Amdahl's law says the floor is the sequential part.
Distribution — many machines, one promise
Replicate state across nodes; pretend it's one machine. The CAP theorem is the price tag: pick two of consistency, availability, partition-tolerance.
Sharding — divide the world to scale it
If state is too big for one node, chop it into independent slices keyed by user, region, hash. Cross-shard transactions are where the dragons live.
Edge — concurrency in space
Move computation toward the user. Latency falls, sovereignty rises. The cloud was a pendulum and it's swinging back to the device.
Privacy & Security
Privacy is the engineered right to reveal selectively. Cryptography is the toolbox. Symmetric keys hide content. Asymmetric keys distribute trust. Zero-knowledge proves without revealing. MPC lets adversaries compute together. All are answers to one question: who is allowed to know?
Symmetric crypto — one key, two parties
AES, ChaCha. If both sides already share a secret, you get speed and confidentiality. The unsolved half is how the secret got there in the first place.
Asymmetric crypto — whispering in public
RSA, elliptic curves. Two keys; one shouted, one whispered. The mathematical impossibility of eavesdropping. Every secure connection on Earth starts here.
Zero-knowledge — prove without telling
Prove you know the password, the path, the balance — without revealing it. The same primitive that compresses a long computation also conceals its inputs.
MPC — adversaries computing together
n parties each hold a secret; together they compute a function over those secrets without any one of them learning the others. Useful when there is no trustworthy host.
Pick a system. See its recipe.
Most real systems are recipes — two or three primitives stacked together. The size of each square tells you how central the primitive is.
ZK-native L2: compression and privacy are the same lever, ordering is its sequencer, concurrency is its sharded prover.
Compress an L2 block's state-transition into one verifiable proof. Three primitives in one envelope.
Order on top of crypto on top of concurrency. Money as an opinion about sequence.
Compress the web into an index, sort it by relevance, serve it with massive concurrency.
Bitcoin's idea plus a programmable ordering — every smart contract is a clause on the sequence.
Compress the corpus into weights, sample tokens in order, run batches of them in parallel.
Content-addressed compression of file states, plus a causal ordering of commits.
A distributed naming service. Concurrency at planetary scale, with a hierarchical ordering of trust.
Privacy through layered encryption, plus the concurrency of a volunteer network.
Asymmetric crypto bootstraps a symmetric session. The web's privacy layer in two acts.
Why only four?Because everything elseis plumbing.
Pick any hard system you can think of. Strip away the framework du jour, the cloud provider, the language. What is left? It will be one of these four shapes — usually a few of them stacked. Compression turns mass into representation. Ordering turns concurrence into sequence. Concurrency keeps the sequence from collapsing under load. Privacy controls who is allowed to read it. Everything else — the wire formats, the container runtimes, the build tools — is plumbing. Important plumbing. But still plumbing.