Introduction to Computer Organization

Introduction to Computer Organization

Computer Organization deals with the structure and behavior of computer systems at the hardware level. It focuses on how the CPU, memory, and I/O devices work together to execute programs.

What is Computer Organization?

Computer Organization refers to the operational units and their interconnections that realize the architectural specifications. It includes:

• Hardware components and their connections
• Instruction execution cycle
• Memory hierarchy
• I/O operations
• Performance optimization

Computer System Components

1. Central Processing Unit (CPU)

• ALU (Arithmetic Logic Unit): Performs arithmetic and logical operations
• Control Unit: Directs operations of the processor
• Registers: Fast storage locations within CPU
• Cache: Small, fast memory close to CPU

2. Memory System

• Primary Memory (RAM): Volatile, fast storage
• Secondary Memory: Non-volatile, slower storage (disk)
• Cache Memory: Very fast, small memory

3. Input/Output System

• I/O Devices: Keyboard, mouse, display, disk
• I/O Controllers: Interface between CPU and devices
• Buses: Communication pathways

Basic Computer Architecture

Von Neumann Architecture

• Single memory for both data and instructions
• Sequential instruction execution
• Stored program concept

Components:

• Memory Unit
• ALU
• Control Unit
• Input/Output

Harvard Architecture

• Separate memories for data and instructions
• Can fetch instruction and data simultaneously
• Used in some embedded systems

Instruction Execution Cycle

Fetch-Decode-Execute Cycle

1. Fetch: Get instruction from memory
2. Decode: Determine what operation to perform
3. Execute: Perform the operation
4. Store: Write results back (if needed)

Steps:

• PC (Program Counter) contains address of next instruction
• Instruction fetched from memory address in PC
• Instruction decoded by control unit
• ALU performs operation
• Results stored in registers or memory
• PC incremented or updated

GATE CS Weightage

Computer Organization typically accounts for:

• 8-12 marks out of 100 in GATE CS
• Medium-high priority subject
• Requires understanding of hardware concepts

Important Topics for GATE CS

1. CPU Design (High Priority)

• Instruction formats
• Addressing modes
• ALU operations

1. Memory Hierarchy (High Priority)

• Cache memory
• Virtual memory
• Memory management

1. Pipelining (High Priority)

• Pipeline stages
• Hazards and solutions

1. I/O Organization (Medium Priority)

• Interrupts
• DMA
• I/O interfaces