Computer Systems Notes

Introduction to Computer Systems

  • Evolution of Computers
  • Computer Memory: Needed to store data and instructions for processing.

Memory Types

  • Main or Primary Memory: Commonly referred to as 'memory.' It is an essential component where programs and data are loaded before processing. The CPU interacts directly with primary memory. Types include:
    • RAM (Random Access Memory): Volatile; data is retained as long as power is supplied.
    • ROM (Read Only Memory): Non-volatile; contents are not lost when power is off; used for startup programs (boot loader).
    • Cache Memory: A very high-speed memory placed between the CPU and primary memory. Stores copies of frequently accessed data from primary memory.
  • Secondary Memory (Storage Device): Auxiliary memory for permanently storing data or instructions. Non-volatile with larger storage capacity than primary memory but slower and cheaper than main memory. Examples include HDD, CD/DVD, Memory Card, SSD, Pen Drives.

Units of Memory

  • Computer systems use binary numbers to store data.
  • Binary digits (0 and 1) are called bits.
    • 4 bits = Nibble (e.g., 1001)
    • 8 bits (two nibbles) = Byte (e.g., 01000110)
  • Units of memory:
    • KB (Kilobyte) = 10241024 Bytes
    • MB (Megabyte) = 10241024 KB
    • GB (Gigabyte) = 10241024 MB
    • TB (Terabyte) = 10241024 GB
    • PB (Petabyte) = 10241024 TB
    • EB (Exabyte) = 10241024 PB
    • ZB (Zettabyte) = 10241024 EB
    • YB (Yottabyte) = 10241024 ZB

Data Transfer

  • Data Transfer Between Memory and CPU: Data is transferred between CPU and primary memory and between primary and secondary memory.
  • Bus: Data transfer uses physical wires called a bus.
    • Data bus: Transfers data between components (bidirectional).
    • Address bus: Transfers addresses between CPU and main memory (unidirectional).
    • Control bus: Communicates control signals between components (unidirectional).
    • System bus: Collectively, these buses make up the system bus.
  • The CPU places the address of the memory location on the address bus to read or write data.
  • The CPU specifies read or write control signals through the control bus.
  • Memory Controller: A memory controller manages the flow of data into and out of the computer's main memory.

Microprocessors

  • A processor (CPU) implemented on a single microchip.
  • Microprocessors carry out data processing, arithmetic, and logical operations.
  • Built over integrated circuits with millions of components like resistors, transistors, and diodes.
  • Evolution: increased processing capability, decreased physical size, reduced cost.
  • Capable of processing millions of instructions per millisecond.
  • Microprocessor Specifications:
    • Word Size: The maximum number of bits a microprocessor can process at a time.
    • Memory Size: The size of RAM varies depending on the word size.
    • Clock Speed: The number of pulses generated per second (measured in GHz).
    • Cores: Basic computation units within the CPU (dual-core, quad-core, octa-core).

Microcontrollers

  • A small computing device with a CPU, RAM, ROM, and other peripherals embedded on a single chip.
  • Examples: Keyboard, mouse, washing machine, digital camera, pendrive, remote controller, microwave.
  • Designed for specific tasks, reducing size and cost.
  • Embedded in devices or systems to perform specific functionality.
  • Enable automation of repetitive tasks without human intervention.

Data and Information

  • Data: Raw, unorganized facts that are processed to get meaningful information. A computer considers everything as data.
  • Data and Its Types: Data can be input in various forms, internally stored in binary form (0 and 1).
    • Structured Data: follows a strict record structure, organized in row/column format, easily understandable (e.g., monthly attendance records).
    • Unstructured Data: Not organized in a pre-defined format (e.g., audio and video files, text documents).
    • Semi-structured Data: No well-defined structure but maintains internal tags (e.g., email, HTML page).

Data Capturing, Storage, and Retrieval

  • Data Capturing: Gathering data from different sources in a digital form (e.g., keyboard, barcode readers, social media posts).
  • Data Storage: Storing captured data for later processing (e.g., digital storage devices).
  • Data Retrieval: Fetching data from storage devices for processing.

Data Deletion and Recovery

  • Deleted data can be recovered if not overwritten.
  • Concerns: unauthorized deletion and unwanted recovery.
  • Mitigation: Limit access, use passwords, encrypt files, and use proper tools to delete or shred data.

Software

  • A set of instructions that operates the hardware. Without it the hardware components cannot function.
  • Need of Software: Makes computer hardware useful and operational. Acts as an interface between users and hardware.
  • System Software: Provides basic functionality to operate a computer (e.g., operating systems, system utilities, device drivers).
    • Operating System: Manages computer operations, resources, access, and security (e.g., Windows, Linux, Android, iOS).
    • System Utilities: Used for maintenance and configuration (e.g., disk defragmentation tool, anti-virus software).
    • Device Drivers: Ensures proper functioning of a particular device; acts as an interface between the device and the operating system.
  • Programming Tools: Used for writing instructions (code) for the computer. Includes programming languages and language translators.
  • Application Software: Meets specific user requirements (e.g., word processing, video playback).
    • General Purpose Software: Developed for generic applications (e.g., LibreOffice, Adobe Photoshop).
    • Customized Software: Tailor-made for specific organizations or individuals (e.g., websites, school management software).

Proprietary or Free and Open Source Software

  • Free and Open Source Software (FOSS): Source code and software are freely available (e.g., Ubuntu, Python).
  • Freeware: Software is freely available, but the source code may not be available (e.g., Skype, Adobe Reader).
  • Proprietary Software: Software purchased from a vendor with copyright (e.g., Microsoft Windows, Tally, Quickheal).

Operating System

  • A resource manager managing hardware resources, application software, and device drivers.
  • Objectives: provides services for building and running applications and provides the user interface.

OS User Interface

  • Command-based Interface: Requires entering commands (e.g., MS-DOS, Unix).
  • Graphical User Interface (GUI): Uses icons, menus, and visual options (e.g., Microsoft Windows, Ubuntu, Macintosh).
  • Touch-based Interface: Uses touch input (e.g., Android, iOS, Windows 8.1 and 10).
  • Voice-based Interface: Uses voice commands (e.g., iOS (Siri), Android (Google Now), Windows 10 (Cortana)).
  • Gesture-based Interface: Uses gestures like waving, tilting, and eye motion (smartphones and laptops).

Functions of Operating System

  • Process Management: Manages and allocates CPU resources to processes.
  • Memory Management: Allocates and frees memory to running processes.
  • File Management: Creates, updates, deletes, and protects files in the secondary memory.
  • Device Management: Manages I/O devices and hardware connected to the computer system.