Unit I — Major Components & Block Diagram of a Computer

A computer system is made up of several interconnected hardware components. Understanding these components and how they communicate with each other is fundamental to computer science.

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Block Diagram of a Computer

The basic block diagram of a computer consists of five major units:

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1. Input Unit

• Accepts raw data and instructions from the user.
• Converts input into binary form that the computer understands.
• Devices: Keyboard, Mouse, Scanner, Microphone, Joystick

2. Central Processing Unit (CPU)

The brain of the computer. Consists of three sub-units:

• Arithmetic Logic Unit (ALU): Performs arithmetic (+, −, ×, ÷) and logical (AND, OR, NOT, compare) operations.
• Control Unit (CU): Directs and coordinates all operations; fetches, decodes, and executes instructions.
• Registers: Small, ultra-fast storage locations inside the CPU for immediate data and address holding.

3. Memory Unit

• Primary Memory: Directly accessible by the CPU — includes RAM and ROM.
• Secondary Memory: Permanent storage — Hard disks, SSDs, CDs, DVDs.

4. Output Unit

• Receives processed results from the CPU and presents them in human-readable form.
• Devices: Monitor, Printer, Speaker, Projector

5. Communication/Bus System

Data travels between components via buses:

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Data Flow in a Computer

1. User enters data via an input device.
2. Data is stored temporarily in primary memory (RAM).
3. The CPU fetches instructions, processes data using ALU, and stores results.
4. Final results are sent to the output device or saved to secondary storage.

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Von Neumann Architecture

Most modern computers follow the Von Neumann model, which states:

• Programs and data share the same memory space.
• Instructions are fetched and executed sequentially.
• The CPU reads instructions from memory one at a time.

Key Takeaway: The computer's architecture revolves around the CPU, memory, and I/O units linked by buses. The Von Neumann model — stored program concept — is the foundation of all modern computers. The CPU's ALU, CU, and registers work together to execute every instruction.