Draw the block diagram of computer system. Explain the input and processing units. [4+6]

Block Diagram of a Computer System

The block diagram of a computer system consists of five main components:

1. Input Unit
2. Central Processing Unit (CPU)
3. Memory Unit
4. Control Unit (CU)
5. Arithmetic Logic Unit (ALU)
6. Output Unit

The diagram above illustrates these components and their interconnections. The Input Unit receives data from external sources (e.g., keyboard, mouse), which is then sent to the CPU for processing. The CPU consists of the Control Unit (CU) and the Arithmetic Logic Unit (ALU). The CU manages and coordinates operations, while the ALU performs arithmetic and logical computations. The Memory Unit temporarily stores data and instructions for quick access. Finally, the Output Unit displays or sends the processed results to external devices (e.g., monitor, printer).

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Explanation of Input Unit

The Input Unit is responsible for receiving raw data and instructions from external sources and converting them into a form that the computer can process. It acts as an interface between the user and the computer system. Common input devices include:

• Keyboard: Used for typing text and commands.
• Mouse: Used for pointing and selecting options.
• Scanner: Converts physical documents into digital format.
• Microphone: Captures audio input for voice recognition or recording.
• Joystick: Used in gaming and specialized applications for controlling movement.

The input unit ensures that data is accurately entered into the system, which is then passed to the CPU for further processing.

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Explanation of Processing Unit (CPU)

The Central Processing Unit (CPU) is the brain of the computer system. It performs all the necessary computations and processing tasks. The CPU consists of two main sub-units:

1. Control Unit (CU)

The Control Unit manages and coordinates the operations of the computer system. Its primary functions include:

• Instruction Fetching: Retrieves instructions from memory.
• Instruction Decoding: Interprets the fetched instructions.
• Instruction Execution: Sends control signals to other components (e.g., ALU, memory) to execute the instructions.
• Synchronization: Ensures that operations are performed in the correct sequence.

The CU acts as a traffic controller, directing data and instructions to the appropriate components for processing.

2. Arithmetic Logic Unit (ALU)

The Arithmetic Logic Unit performs arithmetic and logical operations. Its key functions include:

• Arithmetic Operations: Addition, subtraction, multiplication, and division.
• Logical Operations: AND, OR, NOT, XOR, and comparison operations (e.g., greater than, less than).
• Bitwise Operations: Shifting, rotating, and masking bits.

The ALU works in conjunction with the CU to execute instructions efficiently. For example, when calculating the sum of two numbers, the ALU performs the addition, while the CU ensures that the result is stored correctly in memory.

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How Input and Processing Units Work Together

1. Data Input: The user enters data through an input device (e.g., typing on a keyboard).
2. Data Conversion: The input unit converts the raw data into binary format (0s and 1s), which the computer can understand.
3. Data Transfer to CPU: The binary data is sent to the CPU for processing.
4. Instruction Fetching and Decoding: The CU fetches the instruction from memory and decodes it.
5. Execution by ALU: The ALU performs the required arithmetic or logical operation.
6. Result Storage: The processed result is stored in memory or sent to the output unit for display.

For example, if a user types "2 + 3" on a calculator:

• The keyboard (input unit) sends the numbers and the "+" symbol to the CPU.
• The CU decodes the instruction to perform addition.
• The ALU adds the two numbers (2 + 3 = 5).
• The result (5) is displayed on the screen (output unit).

This seamless interaction between the input and processing units ensures that the computer performs tasks efficiently and accurately.