Computer Architecture

 

Basic Architecture of a Computer

A computer system is organized into several key components that work together to perform operations. These components are based on the Von Neumann architecture, which includes the CPU, memory, input/output devices, and interconnections. Here is a detailed explanation of the core components:

---

1. Central Processing Unit (CPU)

The CPU is the brain of the computer, responsible for executing instructions. It consists of three main subcomponents:

• Arithmetic Logic Unit (ALU):

  • Performs arithmetic operations (addition, subtraction, multiplication, division).
  • Executes logical operations (AND, OR, NOT, XOR) for decision-making.
  • Works directly with data fetched from registers or memory.

• Control Unit (CU):

  • Directs and coordinates the activities of the computer.
  • Decodes instructions fetched from memory and sends control signals to other components (ALU, memory, I/O).
  • Ensures instructions are executed in the correct sequence.

• Registers:

  • Small, high-speed storage locations inside the CPU.
  • Temporarily hold data, instructions, or intermediate results.
  • Common registers include the Accumulator (ACC) for operations, Instruction Register (IR) for holding current instructions, and Program Counter (PC) for tracking the next instruction.

---

2. Memory

Memory stores data and instructions that the CPU needs to execute tasks. It is divided into:

• Primary Memory (RAM):

  • Temporary storage that holds data and instructions while tasks are being executed.
  • Volatile in nature; data is lost when the computer is turned off.

• Secondary Memory:

  • Non-volatile storage like hard drives, SSDs, and external storage for long-term data retention.

• Cache Memory:

  • A small, fast memory inside or near the CPU.
  • Holds frequently accessed data to speed up processing.

---

3. Input/Output (I/O) Devices

• Input Devices: Allow users to interact with the computer (e.g., keyboard, mouse, scanner).
• Output Devices: Display results of computations (e.g., monitor, printer, speakers).

I/O devices communicate with the CPU via I/O controllers and buses.

---

4. System Bus

The components communicate through buses, which are shared pathways for data transfer:

• Data Bus: Transfers actual data between CPU, memory, and I/O.
• Address Bus: Transfers memory addresses where data is stored.
• Control Bus: Transfers control signals from the Control Unit to other parts of the system.

---

Interaction Flow

1. Fetch: The CPU fetches instructions from memory using the address stored in the Program Counter.
2. Decode: The Control Unit decodes the fetched instruction and prepares the ALU or other units to execute it.
3. Execute: The ALU or other units perform the operation, and results may be stored in registers or memory.
4. I/O: Data can be sent to output devices or received from input devices.

This architecture enables computers to execute tasks systematically and efficiently.