Notes on Computer Organization and Architecture (CST 202)

Introduction

• Computer: A device that accepts input, processes data, stores data, and outputs results based on stored instructions.
• Software: Programs that instruct the computer on tasks.
• Hardware: Physical components and devices that process data.
• Peripheral Devices: Enhance input, output, and storage capabilities.
• Network: Connected computers/devices for data sharing.

Computer Types

• Classified by speed, cost, power, and application type.

Computer Organization vs. Architecture

• Organization: How hardware components operate and connect to form a system.
• Architecture: Structure and behavior of the computer system as seen by the user.

Functional Units

• Input Unit: Devices like keyboards/mice for data entry.
• Output Unit: Devices like screens/printers for displaying results.
• Memory Unit:
  • Primary Storage: RAM, used for immediate access data.
  • Secondary Storage: External devices like HDDs.
• ALU: Executes arithmetic and logic operations.
• Control Unit: Directs operations within the computer.
• CPU: Comprises ALU, Control Unit, and Memory Unit.

Basic Operational Concepts

• Instructions stored in memory are executed by fetching them into the processor.
• Instruction Components:
  • IR (Instruction Register): Current instruction.
  • PC (Program Counter): Next instruction's address.

Bus Structures

• A communication pathway for transferring data.
• Memory-Mapped I/O: I/O devices using the same address space as memory.

Memory Locations and Addresses

• Memory: Organized in words, typically 16 to 64 bits long.
• Byte-Addressable Memory: Each byte has a unique address.
• Endianness:
  • Big-Endian: Higher addresses for significant bytes.
  • Little-Endian: Higher addresses for less significant bytes.

Instructions and Instruction Sequencing

• Types:
  • Data transfers.
  • Arithmetic and logic operations.
  • Program sequencing and control.
  • I/O transfers.
• Execution Cycle:
  1. Fetch instruction to IR.
  2. Decode and execute instructions.
  3. PC incremented to the next instruction.
• Branch Instructions: Modify execution sequence based on conditions.

Addressing Modes

• Register Mode: Operands in processor registers.
• Immediate Mode: Constant value in the instruction.
• Indirect Mode: Operand address in a register.
• Index Mode: Operand address from register and constant.
• Relative Mode: Address relative to PC.

Execution of Instructions

• Single Bus Organization: ALU and registers connected by a single bus.
• Multiple Bus Organization: More pathways for faster operations.
• Steps:
  1. Transfer data.
  2. Perform ALU operations.
  3. Fetch from memory.
  4. Store to memory.

Summary

• Instruction execution involves fetching, decoding, executing, and storing results.
• Understanding of architecture and organization is crucial for optimizing computer performance.