Computer Systems

Hardware and Software

Hardware

• It includes the physical components or parts of a computer that you can touch and see.

• Examples:

  • Input Devices: allows users to input data. e.g. Keyboard, mouse, microphone

  • Output Devices: devices that output data from the system. e.g. Monitor, printer, speakers

  • Storage Devices: stores data. e.g. SSD, HDD, USB drive

  • Processing Devices: processes instructions and renders images. e.g. CPU, GPU

Software

• Set of programs or instructions that control the hardware and are used to operate computers and perform tasks.

• Types:

  • System Software: Operating systems, utilities, drivers

  • Application Software: Word processors, web browsers, games

Central Processing Unit (CPU)

Purpose

• It is also known as the center, main processor, or brain of a computer. It executes instructions, processes data, and performs calculations.

Components

• Control Unit (CU): Manages execution of instructions.

• Arithmetic Logic Unit (ALU): Performs calculations and logic.

• Registers: small and fast storage located within the CPU used to store temporary data.

• Cache: a small and very fast memory that stores frequently accessed data.

Buses

• Data Bus: Transfers data between the CPU and memory

• Address Bus: Transfers memory addresses or location of data.

• Control Bus: Sends control signals from CPU to other components.

The Fetch-Decode-Execute Cycle:

• Fetch: Instruction is fetched from memory (RAM) into a register

• Decode: Instruction fetched is interpreted by the Control unit.

• Execute: the CPU carries out Instruction decoded.

Von Neumann Architecture

• A computer design model where the CPU uses a single or shared memory space to store both instructions and data.

• Uses a single bus system for fetching both instructions and data.

• Registers involved:

  • PC (Program Counter): Tracks the next instruction address.

  • MAR (Memory Address Register): Holds address of data to be fetched.

  • MDR (Memory Data Register): stores data being transferred to or from memory.

  • Accumulator: Stores intermediate data results.

Logic gates

• A group of transistors connected together to give one or more outputs, each output based on the input or combination of inputs supplied to it.

• Types:

  • AND gates- output is 1 or TRUE only if both of the inputs are 1.

  • OR gates- The output is 1 only if either or both of the inputs are 1.

  • NOT gates- the output is 1 if the input is 0 (FALSE), and the output is 0 if the input is 1.

  • XOR gates- The XOR gate outputs 1 when any input is 1. But unlike the OR gate, when both input 1 , the OUTPUT is 0.

Memory and Storage

Primary Storage

• RAM (Random Access Memory):

  • Volatile memory – loses its contents when power is off.

  • Stores data and instructions currently in use.

• ROM (Read-Only Memory):

  • Non-volatile memory – keeps its contents when power is off.

  • Used to store the BIOS/firmware

Secondary Storage

• Used for long-term data storage and stores data and programs not currently in use.

• Types:

  • Magnetic storage:

    • Uses spinning magnetic disks.

    • Large capacity, cheaper per GB, but slower and has moving parts

    • Example: Hard drive disks

  • Optical storage:

    • Uses lasers to read/write data.

    • Low cost, but limited storage capacity and slow speed.

    • Example: CDs or DVDs

  • Solid-State storage:

    • Uses flash memory.

    • Fast access times, durable (no moving parts), but more expensive per GB.

    • Example: SSDs and USB flash drives

Tertiary Storage:

• Primarily used for backup, e.g. magnetic tape.

Embedded Systems

• Computers within a larger system, dedicated to perform specific tasks.

• Examples:

  • Washing machines, microwaves,

• Features:

  • Limited functions

  • Low power

  • Real-time performance

  • Reliable and cheap

System Software

Operating System (OS)

• Software that manages computer hardware and software resources.

• Functions:

  • Memory management

  • Processor management

  • File and disk management

  • User interface (GUI/CLI)

  • Security management

  • Multitasking

Utility Software:

• Tools to maintain and optimize system performance

• Examples:

  • Antivirus

  • File compression

  • Backup software

  • Disk defragmentation

Factors Affecting CPU Performance

• Clock Speed: Measured in GHz. Determines how many instructions per second the CPU can process.

• Number of Cores: Each core can execute instructions independently. More cores means more multitasking.

• Cache Size: Bigger cache reduces time the CPU spends accessing data from RAM.

• Processor Architecture: Affects efficiency of instruction handling

The Basic Input Output System

• Firmware stored in ROM. It initializes hardware during the startup process and loads the bootloader that launches the operating system

• Functions:

  • Performs Power-On Self-Test (POST) to check hardware.

  • Loads bootloader to start the operating system.

  • Provides basic hardware control before the OS takes over..

Virtual Memory

• Used when RAM is full.

• Part of the secondary storage is used as extra RAM.

• Slower than actual RAM.

• Can cause disk thrashing if overused.