The central processing unit (CPU) is the "brain" of a computer. It fetches instructions from memory, decodes them and executes them.
Components
ALU (arithmetic logic unit): performs calculations and logical comparisons.
Control unit (CU): directs the operation of the CPU, controlling the flow of data and instructions.
Registers: very fast storage inside the CPU: program counter (PC) (address of the next instruction), memory address register (MAR), memory data register (MDR), accumulator (ACC) (stores results).
Cache: small, very fast memory close to the CPU holding frequently used data.
CPU components
The fetch-decode-execute cycle
Fetch: the PC's address is copied to the MAR; the instruction at that address is fetched into the MDR; the PC increments.
Decode: the control unit decodes the instruction.
Execute: the instruction is carried out (the ALU may calculate).
Fetch, decode and execute
Performance
Clock speed (GHz: cycles per second), number of cores (more can run tasks in parallel), and cache size affect speed.
Multiple processor cores
Von Neumann architecture
Instructions and data are stored in the same memory. Embedded systems (e.g. washing machine controller) are dedicated computers.
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