Which of the following is NOT a component of a CPU?

The correct answer is D, Hard Disk. A hard disk is a secondary storage device that keeps programs and files permanently, even when the power is off, and it sits outside the processor. The CPU (Central Processing Unit), often called the brain of the computer, is made of the Arithmetic Logic Unit, the Control Unit and a set of small, very fast registers. Modern processors also carry cache memory on the same chip to hold the data and instructions they need most often. Data from the hard disk is first loaded into RAM, then moved into the cache and registers before the CPU works on it. A is wrong because the ALU does all arithmetic and logical work such as addition and comparison. B is wrong because the Control Unit fetches and decodes instructions and directs every operation. C is wrong because cache memory is built into the processor chip and is the fastest memory after the registers. Exam tip: CPU = ALU + CU + registers (with cache); hard disk = secondary storage.