Computer Science › Computer Architecture

CPU

The processor that executes instructions.

Also known as: processor, central processing unit

The CPU (central processing unit) is the chip that executes a program’s instructions: arithmetic, comparisons, moving data and jumping between instructions. Everything your code does ultimately becomes a long stream of such tiny operations.

What it does

It repeats a cycle billions of times per second: fetch an instruction from memory, decode it, execute it, and store the result. The clock speed (measured in GHz) is how fast that rhythm runs, though how much work gets done per tick varies between designs.

Related parts

• Cores: modern CPUs contain several independent processing units, so multiple things can run at once (CPU cores).
• Registers: a few tiny, very fast storage slots inside the chip.
• Cache: small, fast memory on the chip that holds recently used data, because RAM is much slower than the CPU.
• Instruction set: the family of instructions it understands (x86-64, ARM). A program compiled for one doesn’t run on the other (word size).

Why it matters for developers

• CPU-bound vs I/O-bound work. A program that spends its time computing is limited by the CPU. One that waits for the network or disk isn’t (concurrency vs parallelism).
• High CPU usage is a performance signal: infinite loops, heavy computation, inefficient algorithms (time complexity).
• Memory access patterns matter. Arrays walk memory in order, which the cache likes. Chasing pointers doesn’t.
• Cloud sizing: instance types list vCPUs, and you choose by workload (capacity planning).
• Load average and utilization tell you whether a server is busy (system monitoring tools).

GPUs are specialized processors for many parallel simple operations, used for graphics and machine learning. The CPU remains the general-purpose coordinator.