Lecture 2 CompSci

Introduction to Computers

Definition of a Computer

• A computer is defined as a device that:

  • Takes input

  • Processes this input according to stored instructions

  • Produces results as output.

Computer Hardware

Components of Hardware

• Hardware refers to all electronic and mechanical equipment in a computer, including:

  • Storage: Hard disk

  • Memory: RAM

  • Processor: CPU (Central Processor Unit)

  • Input Devices: Keyboard, mouse

  • Output Devices: Monitor

  • Cables

Basic Computer Organization

Structure of a Computer System

• Key components include:

  • CPU/Processor

  • Memory Subsystem

  • I/O Devices

Data Buses

• Address Bus: Carries the address to access data

• Data Bus: Transmits the actual data

• Control Bus: Carries control signals

Central Processing Unit (CPU)

Function of the CPU

• The CPU executes programs by performing four main steps:

  1. Fetch: Retrieve an instruction from program memory.

  2. Decode: Break down the instruction into parts relevant to the CPU.

  3. Execute: Different portions of the CPU perform the required operations.

  4. Write Back: Store the results of execution if necessary.

Organization of the CPU

• Components include:

  • Control Unit: Directs the execution of instructions.

  • Execution Units: Perform specific operations (e.g., arithmetic).

  • Register File: Contains information necessary for current instruction execution.

Memory Subsystem

Types of Memory

• Memory is organized into numbered storage locations:

  • Nonvolatile Memory:

    • Retains data when the system is shut down.

    • Typically has a higher capacity yet slower than volatile memory.

  • Volatile Memory (Primary Memory):

    • Loses data when powered off.

    • Examples include Cache Memory and RAM.

Primary Memory

• Essential for CPU functionality and directly connected to it.

• Types include:

  • Registers: Store data the CPU needs for instructions.

  • Main Memory: Contains currently executed programs and operational data.

  • Cache Memory: A fast, small internal memory enhancing CPU performance.

Input/Output Subsystem

I/O Devices

• Input Devices: Feed data into the computer (e.g., keyboard, mouse).

• Output Devices: Display or transmit information back to the user (e.g., monitors, printers).

• I/O devices communicate with the processor via the I/O bus, commonly using PCI Express in PCs.

Summary of Key Components

• Despite differences in hardware across computing devices, they all share core components:

  • CPU

  • RAM

  • I/O Devices

  • Busses