Computer Architecture: CPU Structure – Control Unit, ALU, Registers & Fetch-Decode-Execute
This article is a term explanation for the CPU – including exam questions and tags.
In a Nutshell
The CPU is the heart of every computer – it executes commands, processes data, and controls all essential operations in the system.
Compact Technical Description
The CPU (Central Processing Unit) is the central processing unit of a computer. It consists of the control unit, the ALU (Arithmetic Logic Unit), and various registers. The control unit interprets machine instructions and coordinates data flow. The ALU handles mathematical and logical operations. Registers serve as fast storage locations for temporary data. Modern CPUs are mostly multi-core processors with multiple logical units (cores) and feature cache memory for performance optimization. CPU performance depends on factors such as clock frequency, architecture, cache size, and number of cores.
Exam-Relevant Key Points
- CPU is the computing and control center of the system
- Consists of control unit, ALU, registers
- Performs arithmetic, logical, and control operations
- Works according to the Fetch-Decode-Execute cycle (IHK-relevant)
- Registers are extremely fast temporary storage
- Weak CPUs can reveal security vulnerabilities like Spectre
- Multi-core increases computing power with lower energy consumption
- CPU structure and functionality must be documented
Core Components
- Control Unit
- ALU (Arithmetic Logic Unit)
- Register set
- Program Counter (instruction counter)
- Instruction Register
- Data bus interface
- Cache (L1, L2, L3)
- Clock generator
- Instruction set
- Interrupt control
Practical Example
// Example: Addition command ADD R1, R2
An addition command ADD R1, R2 is decoded in the control unit →
ALU adds the values from register R1 and R2 →
Result is stored in register R1.
Explanation: The CPU cycle controls instruction execution:
1. Fetch (load)
2. Decode (decode)
3. Execute (execute)
Advantages and Disadvantages
Advantages
- Universally programmable
- High computing speed
- Parallel processing through multicore
- Complex control logic can be implemented
Disadvantages
- Dependence on instruction set
- High heat generation under high load
- Limited internal memory (number of registers)
Typical Exam Questions (with Short Answer)
- Main task of the CPU? Executes commands, processes data, and controls system components.
- Main components of the CPU? Control unit, ALU, registers.
- Registers in the CPU? Fast memory for temporary data within the CPU.
- CPU instruction cycle? Fetch → Decode → Execute.
- Program Counter? Register containing the address of the next instruction.
- CPU cache vs. RAM? Cache is faster and closer to the CPU, but smaller than RAM.
- Are multicore CPUs more powerful? Can process multiple instruction streams simultaneously.
- ALU and its tasks? Component for arithmetic and logical operations.