Computer System Overview Notes

Computer System Overview

1.1 Introduction

• Computers have revolutionized the world, impacting various aspects of life.
• Modern life is unimaginable without computers and related technologies like email, internet, and smartphones.
• Computers efficiently deliver results due to the combination of hardware and software.
• Hardware: Physical electronic components (e.g., keyboard, CPU, monitor).
• Software: Recorded instructions and programs that govern the computer's operation. A program is a set of instructions for a specific task.

1.2 Computer Components and Basic Computer Organization

• A computer system has five basic components:
  • Input Unit: Takes input for the computer via input devices.
  • Output Unit: Produces output information via output devices.
  • Central Processing Unit (CPU): Processes data and instructions.
    • Arithmetic and Logic Unit (ALU): Carries out arithmetic (add, subtract, multiply, divide) and logical operations (greater than, less than, equal to).
    • Control Unit: Controls and supervises processing.
  • Primary Memory: Internal volatile memory for storing data and instructions during processing.
  • Secondary Storage Unit: External storage devices for permanent memory.
• The physical structure is made up of computer system components, while the logical structure is defined as Computer Organization.

1.2.1 Computer Organisation

• Computer organization describes how components are connected, how they affect each other, and how they contribute to the computer's overall performance.
• Computers follow the Input → Process → Output (IPO) principle.
• Computer organization involves components for input, processing, and output.

1.2.2 Input Unit

• Formed by input devices (keyboard, mouse, MICR, OMR, OCR, joystick).
• Responsible for taking input and converting it into computer-understandable binary code.
• Input consists of data and instructions.
• Examples of input devices:
  • Keyboard: Types letters, digits, and commands. Braille keyboards are available for visually challenged users.
  • Mouse: A pointing device that controls the movement of the pointer on the screen.
  • Microphone (Mic): Sends sound input to the computer, converting sound into digitized audio. It requires a sound card.

1.2.3 Output Unit

• Formed by the output devices attached to the computer.
• Converts binary output from the CPU into human-readable form (characters, graphical, audio-visual).
• Examples of output devices:
  • Monitors: Display information using pixels. Braille monitors are available for visually challenged individuals.
  • Printers: Deliver information on paper (inkjet, laserjet, dot-matrix printers). 3D printers can create 3D models.
  • Speakers: Convert electrical signals from the sound card into audible sound.

1.2.4 The CPU (Central Processing Unit)

• The main control center and processing unit, also known as the brain of the computer.
• Sub-components:
  • Arithmetic Logic Unit (ALU): Performs arithmetic ($+, -, *,/$) and logical ($<, >,=, <=,>=,!=$) operations. Results are stored back in memory.
  • Control Unit (CU): Controls and guides the interpretation, flow, and manipulation of data and information. It sends control signals and executes program instructions. It fetches instructions from memory, decodes them, and executes them. The control unit also manages data flow between input/output devices and memory.
  • Registers: Small data-holding places used by the CPU to temporarily store processing information, memory addresses, or instructions.
• Modern smart machines often contain embedded CPUs (microcontrollers) with ROM, RAM, and embedded instructions.

1.2.5 The Memory [Main Memory/Primary Memory]

• The internal workspace where data and instructions are held during processing.
• Each memory location has a unique memory address.
• Memory is cleared after a task is performed.
• A bit is the elementary unit of memory. Eight bits form a byte.
• One byte is the smallest unit representing a data item or character.
• Memory units: KB, MB, GB, TB, PB, EB, ZB, YB.
• Every higher memory unit is equal to $2^{10}$ of its lower unit.

Table 1.1 Units of Computer Memory Measurements

• Secondary memory is needed to store data and information permanently.
• Common secondary storage media: Hard disk, pen drive.

1.2.5A Parts of Main Memory/Primary Memory

• RAM (Random Access Memory): Memory cells can be accessed randomly with equal access time.
• Volatile memory: Contents are erased when power is off.
• Types of RAM chips:
  • Dynamic RAM (DRAM): Made of transistors and capacitors. Access times range from below 20 to 70 nanoseconds.
  • Static RAM: Made of flip-flops; faster access times (about 10 nanoseconds). Used in specialized applications.
• Memory Access Time: The time taken to retrieve data from memory.
• ROM (Read-Only Memory): Performs only read operations; information is permanent and cannot be altered.
• Types of ROM:
  • PROM (Programmable ROM): User-programmable memory. Also called OTP (One Time Programmable).
  • EPROM (Erasable Programmable ROM): Can be programmed and erased multiple times (e.g., using UV radiation).
  • EEPROM (Electrically Erasable Programmable ROM): Erased electrically, faster than UV-EPROM; selective byte erasure is possible.
  • Flash EEPROM: Very fast erasure (less than a second), but erases fully, not selectively.
  • Mask ROM: Programmed by the IC manufacturer.

1.2.6 Cache Memory

• High-speed storage mechanism, either a reserved section of main memory, an independent high-speed storage device, or on the CPU chip.
• The CPU first checks the cache for data; if found (cache hit), it avoids accessing slower main memory.
• Effectiveness is judged by its hit rate.

1.2.7 The Storage Unit

• Used to store and retrieve data for processing.
• Secondary storage devices are used to store large amounts of data permanently due to the limited and non-permanent nature of primary memory.
• Types of storage devices: Hard disks, CDs, DVDs, flash drives, Blu-ray Discs.
• Storage capacity is measured in KB, MB, GB, and TB.

Common Storage Devices:

• Hard Disks: Store information on spinning magnetic platters.
• Compact Disks (CDs): Optical media with a storage capacity of up to 700 MB.
• DVDs: Optical storage device holding about 15 times more information than a CD-ROM, storing up to 17 GB.
• Flash Memory: Solid-state memory devices with no moving parts, retaining data when power is off; range from 256 MB to over 128 GB.
• Blu-Ray Disk: Uses a blue-violet laser for reading and writing data, storing up to 128 GB.

1.2.8 The System Bus

• An electronic pathway that connects major computer components.
• Data and instructions are passed through the system bus.
• Components:
  • Data Bus: Carries data.
  • Control Bus: Carries control instructions.
  • Address Bus: Carries memory addresses.
• I/O Bus: Connects input, output, and external devices to the system.

1.3 Mobile System Organization

• Modern mobile systems are small, battery-powered computers.
• They handle diverse applications, including calls, camera, touch screen, and multimedia content.
• Mobile systems often integrate components onto a single chip (System on a Chip - SoC) to reduce power consumption.

Functional Components:

• Mobile Processor (Mobile CPU):

  • The brain of the smartphone. It Receives commands, performs calculations, plays audio/video, stores information, and sends signals.

    • Communications Processing Unit: Responsible for calls, utilizes a digital signal processor to work with RF Transceiver and the Audio subsystem.
      • Radio Signal Management Unit connects SIM to base stations through radio signals (3G/LTE/4G).
    • Applications Processing Unit (APU): Governs all operations, runs mobile applications (apps).

• Display Subsystem: Provides display facilities, touch-sensitive interface, and touch-sensitive keyboards.

• Camera Subsystem: Delivers image and video experiences; it Includes an Image Signal Processor (ISP) for image capture, high-resolution support, and image stabilization.

• Mobile System Memory:

  • RAM (Random Access Memory): Work memory; apps are loaded and executed from RAM. More RAM improves performance. It is volatile.
  • ROM (Read-Only Memory): Internal storage, not user-writable; typically Flash memory or EEPROM.

• Storage: External storage (SD cards, micro SD cards) for storing pictures, music, and videos.

• Power Management Subsystem (Battery): Provides power to the mobile system. Includes a battery management system, charger, and battery unit.

1.4 Types of Software

• A computer system requires hardware and software for functioning.
• Hardware: Physical components (input devices, output devices, CPU, hard disk, printer).
• Software: Programs that govern the operation of a computer and make the hardware run.
• Categories:
  • System Software
  • Application Software

1.4.1 System Software

• System software controls internal computer operations (reading data, transmitting information, checking components, converting data).
  • Operating System
  • Language Processor

1.4.1A Operating System

• Makes the computer system convenient to use and uses hardware efficiently.
• An interface between the user and the hardware.
• Components include Hardware, Operating System, Application program routines, and Humanware (users).
• Roles: Executes programs and manages computer resources.
• Types: Single user OS, Multiuser OS, Time-sharing OS, Real-time OS, Multiprocessing OS, Distributed OS.

1.4.1B Language Processors/Language Translators

• Translates source code into object code or machine code.
  • Source code: Program code written in a high-level language (HLL).
  • Object code: Code in machine language or binary code.
• Types: assembler, interpreter, and compiler.
  • Assembler: Converts assembly language programs into machine language.
  • Interpreter: Translates and executes instructions line by line.
  • Compiler: Translates and executes instructions in one go.
• Translated machine code offers faster execution.

1.4.2 Application Software

• Software designed for a specific application.
• Examples: Word processing, inventory control, accounting, railway reservation, billing.
• Categories:
  • Packages
  • Utilities
  • Customized Software
  • Developer Tools

1.4.2A Packages

• General application software used by individual users.
• Common categories: Word Processing Software, Spreadsheets, Database Management Systems, Desktop Publishing Software, Graphics, multimedia, and presentation applications.

1.4.2B Utilities

• Helpful programs that ensure the smooth functioning of the computer.
• Assist the computer by solving problems and maximizing potential.
• Examples:
  • Text Editor: Creates and edits text files.
  • Backup Utility: Duplicates disk information.
  • Compression Utility: Compresses large files to take less storage space.
  • Disk Defragmentor: Speeds up disk access by rearranging files and free space.
  • Antivirus Software: Scans for and removes viruses.

1.4.2C Business Software

• Specifically created according to a business' requirements.
• Examples: Inventory Management System, Payroll system, Financial Accounting.
  Customized software meets specific requirements

1.4.3 Software Libraries

• A predefined set of code/functions, classes, scripts etc., available for use in software development.
• Combine codes/functions etc. on the basis of common domain.
• Examples in Python: NumPy (Numerical Python), SciPy (Scientific Python), Panda Library.