Central Processing Unit | UNIT-3 | Class 1st Year

Short Questions

i. What is the function of ALU in the computer?

• Definition: The ALU (Arithmetic Logic Unit) is a digital circuit that performs arithmetic and logical operations.
• Use: It performs operations like addition, subtraction, multiplication, division, AND, OR, NOT, etc.
• Example: When you add two numbers, such as 5 + 3, the ALU processes the operation and outputs the result (8).
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ii. What is the function of the control unit in the computer?

• Definition: The Control Unit (CU) is a component of the CPU that directs the operations of the processor by controlling the flow of data within the system.
• Use: It manages the execution of instructions by sending control signals to the ALU, registers, and other parts of the computer.
• Example: The CU interprets the instructions fetched from memory and coordinates actions like fetching, decoding, and executing the instruction.
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iii. What is a microprocessor?

• Definition: A microprocessor is a small, integrated circuit (IC) that serves as the central processing unit (CPU) of a computer.
• Use: It performs most of the processing in a computer, executing instructions from programs.
• Example: Intel’s Core i7 or AMD Ryzen 5 are examples of microprocessors used in personal computers.
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iv. Define system bus.

• Definition: The system bus is a collection of pathways used for communication between the CPU, memory, and peripheral devices in a computer.
• Use: It allows data to be transferred between the CPU, memory, and input/output devices.
• Example: The system bus consists of data, address, and control buses, which facilitate communication across various components.

v. Write short note on Memory Buffer Register (MBR).

• Definition: The Memory Buffer Register (MBR) is a register in the CPU used to temporarily store data that is being transferred to or from memory.
• Use: It holds the data read from or written to memory, allowing the processor to manage memory operations.
• Example: When data is fetched from memory, it is stored temporarily in the MBR before being sent to the processor.

vi. What is CPU operation?

• Definition: CPU operation refers to the activities carried out by the central processing unit to execute instructions from a program.
• Use: It involves fetching, decoding, and executing instructions.
• Example: When a program is running, the CPU continuously fetches instructions, decodes them to understand what action to take, and then executes those instructions.

vii. What is meant by an instruction?

• Definition: An instruction is a binary-coded operation in a program that tells the computer what action to perform.
• Use: Instructions are executed by the CPU to perform tasks like arithmetic operations, data transfer, and control actions.
• Example: An instruction like “ADD R1, R2” means adding the values in registers R1 and R2 and storing the result back in R1.

viii. Differentiate between op-code and operand?

• Op-code (Operation Code): The part of an instruction that specifies the operation to be performed (e.g., ADD, SUBTRACT).
• Operand: The part of the instruction that specifies the data or address on which the operation is to be performed (e.g., register or memory location).
• Use: Op-codes define the action, and operands define the data or addresses involved in the operation.
• Example: In the instruction ADD R1, R2, "ADD" is the op-code, and "R1" and "R2" are operands.
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ix. Show computer instruction format with the help of a diagram and label its parts.

A typical computer instruction format consists of the following parts:

• Op-code (Operation Code): Specifies the operation to be performed.
• Operand: Specifies the data or addresses involved in the operation.
• Addressing Mode (optional): Specifies how to interpret the operands.
• Instruction Length (optional): Specifies the length of the instruction in bits.

Instruction Format Example:

Op-code Operand Addressing Mode

6 bits 10 bits 4 bits (if required)

Example instruction: ADD R1, R2

x. Differentiate between CISC and RISC processor architecture.

• CISC (Complex Instruction Set Computer): A processor architecture that allows a wide variety of complex instructions in a single machine cycle.
• RISC (Reduced Instruction Set Computer): A processor architecture that uses a smaller set of simple instructions, executed in one machine cycle.
• Use: CISC aims to reduce the number of instructions per program by using complex instructions, while RISC focuses on fast execution by simplifying the instruction set.
• Examples: CISC: Intel x86 architecture. RISC: ARM architecture.

Key Differences:

• CISC: More complex instructions, slower clock speed.
• RISC: Simpler instructions, faster execution.
  
  

Long Questions

i. What is CPU? Describe basic components of CPU in detail.

Definition: The CPU (Central Processing Unit) is the primary component of a computer that carries out most of the processing inside the system. It is often referred to as the brain of the computer, as it interprets and executes instructions from programs.

Explanation: The CPU performs fundamental operations like arithmetic calculations, logical operations, data transfer, and control operations that allow a computer to perform tasks. The CPU interacts with memory and input/output devices to process data and execute instructions.

Basic Components of the CPU:

• Arithmetic Logic Unit (ALU): Performs arithmetic and logical operations like addition, subtraction, etc.
• Control Unit (CU): Manages execution of instructions by directing operations.
• Registers: High-speed storage areas used to temporarily store data or instructions.
• Cache Memory: Small, high-speed memory for frequently used instructions or data.

ii. What is a register? Explain different types of registers.

Definition: A register is a small, fast storage location within the CPU that holds data or instructions temporarily. Registers enable fast access to data that is needed immediately or frequently during processing.

Explanation: Registers are used for various purposes in the CPU, such as holding operands for arithmetic operations, addresses for memory access, or instructions to be executed. Registers provide high-speed data access, which improves the efficiency of the CPU.

Types of Registers:

• Data Register (DR): Holds the data to be processed by the ALU or transferred to/from memory.
• Program Counter (PC): Holds the address of the next instruction to be executed.
• Instruction Register (IR): Stores the current instruction being executed.
• Accumulator (A): Holds intermediate results of arithmetic and logical operations.
• Memory Address Register (MAR): Holds the address of the memory location to be accessed.
• Memory Buffer Register (MBR): Temporarily stores data being transferred to/from memory.

iii. What is a system bus? Explain different types of buses used in computers.

Definition: A system bus is a collection of wires or pathways used for communication between different components of a computer system, such as the CPU, memory, and I/O devices.

Explanation: The system bus facilitates data transfer between the processor, memory, and peripheral devices. It consists of multiple lines (wires) that carry signals between the components. The system bus is typically composed of three primary types of buses: the data bus, the address bus, and the control bus.

Types of Buses:

• Data Bus: Transfers actual data between the CPU, memory, and peripherals.
• Address Bus: Carries memory addresses for reading or writing operations.
• Control Bus: Transfers control signals that manage CPU and system operations.

iv. Explain different types of CPU instructions. Also give examples.

Definition: CPU instructions are binary-coded operations that tell the CPU what task to perform, such as arithmetic operations, data transfer, or control operations.

Explanation: Instructions in a computer program are executed by the CPU to carry out operations. Instructions typically consist of an op-code (operation code) and operand (data or memory address).

Types of CPU Instructions:

• Data Transfer Instructions: Move data between registers or memory. Example: MOV A, B, LOAD R1, 1000.
• Arithmetic Instructions: Perform arithmetic operations. Example: ADD R1, R2.
• Logical Instructions: Perform logical operations. Example: AND A, B.
• Control Instructions: Manage program execution. Example: JMP LABEL.
• Input/Output Instructions: Handle input and output operations. Example: IN R1, PORT1.