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

The Central Processing Unit (CPU) is the primary component of a computer that performs most of the processing inside a computer. It consists mainly of three key internal components: the Arithmetic and Logic Unit (ALU), which handles mathematical calculations and logical operations; the Control Unit (CU), which directs the operation of the processor; and the Memory Unit, often referred to as registers or cache within the CPU context for immediate data storage. A Hard Disk Drive (HDD), however, is an external peripheral device used for long-term data storage and is not part of the CPU's internal architecture. Therefore, Option D is correct because an HDD is a storage device separate from the CPU's core processing units. Options A, B, and C are incorrect because they describe actual functional parts of the CPU itself.