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 four main components:

1. Input Unit
2. Central Processing Unit (CPU)
3. Memory Unit
4. Output Unit

The diagram above illustrates these components and their interconnections.

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Explanation of Input Unit

The Input Unit is responsible for receiving data and instructions from the user or external devices and converting them into a form that the computer can process. It consists of input devices such as:

• Keyboard: Used to input text and commands.
• Mouse: Used for pointing and selecting options.
• Scanner: Converts physical documents into digital format.
• Microphone: Captures audio input.
• Webcam: Captures video input.

The input unit sends the collected data to the CPU for 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 processing tasks, including executing instructions and performing calculations. The CPU consists of three main parts:

1. Control Unit (CU)

• Manages and coordinates the activities of all components.
• Reads instructions from memory and decodes them.
• Sends control signals to other units to execute instructions.

2. Arithmetic Logic Unit (ALU)

• Performs arithmetic operations (addition, subtraction, multiplication, division).
• Performs logical operations (AND, OR, NOT, comparison).
• Stores intermediate results in registers.

3. Registers

• Small, high-speed memory units inside the CPU.
• Store temporary data, instructions, and results.
• Examples: Program Counter (PC), Accumulator (ACC), Instruction Register (IR), Memory Address Register (MAR), Memory Data Register (MDR).

The CPU fetches instructions from memory, processes them, and stores results back in memory or sends them to the output unit.

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Detailed Working of the Processing Unit

The CPU follows a fetch-decode-execute cycle to process instructions:

1. Fetch Cycle:

   • The Program Counter (PC) holds the address of the next instruction.
   • The instruction is fetched from memory and stored in the Instruction Register (IR).
   • The PC is incremented to point to the next instruction.

2. Decode Cycle:

   • The Control Unit (CU) decodes the instruction to determine the operation to be performed.
   • The necessary operands are fetched from memory or registers.

3. Execute Cycle:

   • The ALU performs the required arithmetic or logical operation.
   • The result is stored in a register or memory.

4. Store Cycle (if needed):

   • The result is written back to memory or sent to the output unit.

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Summary of Input and Processing Units

The Input Unit provides raw data, while the CPU (Processing Unit) processes it according to instructions, making the computer functional. The processed data is then sent to the Output Unit for display or storage.