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The Microprocessor
The ALU, control unit and registers — PC, MAR, MDR, CIR and accumulator — each explained with an everyday analogy.
The CPU on One Chip
A microprocessor is a complete CPU on one chip. You met its three main parts in the first course. Now you will see what each one does in detail — and the registers you need to name in assignments.
The Arithmetic Logic Unit (ALU)
The Control Unit (CU)
The control unit also uses the clock: a signal that ticks billions of times a second. Every step the CPU takes is kept in time with the clock, like musicians following a conductor's beat.
Registers
Registers are tiny storage places inside the CPU. Each holds one value — an address, an instruction or a number. They are the fastest memory in the computer. These five are named in most syllabuses:
| The five key registers | ||
|---|---|---|
Cache and the Clock
- Cache is a small amount of very fast memory on the CPU chip. It keeps copies of instructions and data the CPU is likely to need again, so it does not have to wait for RAM. There are levels: L1 (smallest, fastest, inside each core), L2, and L3 (larger, shared by all cores).
- The clock sets the pace. Its speed is measured in gigahertz (GHz): 1 GHz = 1,000 million ticks per second.
Practice
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