Computer System Notes

Introduction to Computer System

• A computer is an electronic device that accepts data (input), processes it, and generates results (output).
• A computer system includes the computer itself along with additional hardware and software.
• A computer system comprises a central processing unit (CPU), memory, input/output devices, and storage devices.
• These components work together to deliver the desired output.
• Computer systems vary in form and size, from high-end servers to personal desktops, laptops, tablets, and smartphones.

Central Processing Unit (CPU)

• The CPU is the electronic circuitry that carries out processing; it's the "brain" of the computer.
• It's also called a processor and is physically placed on integrated circuits (ICs) made of semiconductor materials.
• The CPU receives instructions and data through programs, fetches them from memory, performs arithmetic and logical operations, and stores the result back in memory.
• While processing, the CPU stores data and instructions in local memory called registers, which are limited in size and number.
• Registers are used for storing data, instructions, or intermediate results.
• The CPU has two main components: the Arithmetic Logic Unit (ALU) and the Control Unit (CU).
  • The ALU performs arithmetic and logic operations.
  • The CU controls sequential instruction execution, interprets instructions, and guides data flow through memory, ALU, and input/output devices.
• CPU is also known as a microprocessor.

Input Devices

• Input devices send control signals to a computer and convert input data into a digital form that the computer can accept.
• Examples include keyboard, mouse, scanner, and touch screen.
• Braille keyboards are available for visually impaired users.
• Data can also be entered through voice, such as with Google voice search.
• Data entered through input devices is temporarily stored in the main memory (RAM).
• For permanent storage, data and instructions are stored in secondary memory.

Output Devices

• Output devices receive data from a computer system for display or physical production and convert digital information into human-understandable form.
• Examples include monitors, projectors, headphones, speakers, and printers.
• Braille display monitors assist visually challenged individuals.
• Commonly used printers include inkjet, laserjet, and dot matrix.
• 3D printers build physical replicas of digital 3D designs and are used in manufacturing and medicine.

Evolution of Computer

• Computing devices have evolved from simple calculators to powerful data processors in a relatively short time.
• The Von Neumann architecture consists of a CPU, memory, input/output devices, and communication channels.
• Electronic Numerical Integrator And Computer (ENIAC) is considered the first binary programmable computer based on Von Neumann architecture.
• Large Scale Integration (LSI) in the 1970s allowed the integration of a complete CPU on a single chip, called a microprocessor.
• Moore’s Law predicted exponential growth in the number of transistors on a microchip.
• In the 1980s, Very Large Scale Integration (VLSI) integrated around 3 million components on a chip.
• Super Large Scale Integration (SLSI) now allows fabrication of high density of transistors (approx $10^6$ components) on a single IC.
• IBM introduced its first personal computer (PC) in 1981, and Apple introduced Macintosh machines in 1984.
• The popularity of PCs surged with the introduction of Graphical User Interfaces (GUI).
• The growth of the World Wide Web (WWW) in the 1990s accelerated computer usage.
• Laptops, smartphones, tablets, and personal digital assistants have further advanced personal computing.
• The next wave includes wearable gadgets and smart appliances as part of the Internet of Things (IoT), leveraging artificial intelligence.

Timeline of Computing Technology:

• Abacus: Invented almost 3000 years ago for simple arithmetic calculations.
• Pascaline: Blaize Pascal's mechanical calculator for addition and subtraction (1642).
• Analytical Engine: Charles Babbage's mechanical computing device for inputting, processing, storing, and displaying output (1834); which formed the basis of modern computers.
• Tabulating Machine: Herman Hollerith's machine for summarizing data stored on punched cards (1890).
• Turing Machine: A general-purpose programmable machine capable of solving any problem by executing programs stored on punched cards (1937).
• EDVAC/ENIAC: Computers developed based on John Von Neumann's concept of stored program (1945).
• Transistor: Replaced vacuum tubes, developed at Bell Labs using semiconductor materials (1947).
• Integrated Circuit (IC): A silicon chip containing an entire electronic circuit in a small area (1970).

Computer Memory

• A computer system needs memory to store data and instructions for processing.
• Primary memory (main memory) is what we usually refer to as "memory."
• Secondary memory (storage device) stores data, instructions, and results permanently for future use.

Units of Memory

• A computer system uses binary numbers (0 and 1) called bits to store and process data.
• Bits are grouped together to form words.
• A 4-bit word is called a Nibble.
• An 8-bit word (two nibbles) is called a byte.
• Bytes are grouped together to make bigger units of memory.

Types of Memory

• Computers have two types of memory: primary and secondary.

Primary Memory

• Essential component where programs and data are loaded before processing.
• The CPU interacts directly with primary memory for read/write operations.
• Two types: Random Access Memory (RAM) and Read Only Memory (ROM).
  • RAM: Volatile; retains data as long as power is supplied; used for temporary storage; main memory; faster than secondary memory.
  • ROM: Non-volatile; retains contents even when power is off; used for permanent storage of rarely changed contents like the boot loader.

Cache Memory

• High-speed memory between the CPU and primary memory to speed up CPU operations.
• Stores copies of frequently accessed primary memory locations.
• When the CPU needs to access memory, it first examines the cache.

Secondary Memory

• Auxiliary memory for permanently storing data or instructions for future use.
• Non-volatile, larger storage capacity than primary memory.
• Slower and cheaper than main memory.
• Cannot be directly accessed by the CPU; contents must be brought into main memory first.
• Examples: Hard Disk Drive (HDD), CD/DVD, Memory Card.
• Solid-State Drives (SSD) support faster data transfer speeds.

Data Capturing, Storage, and Retrieval

Data Capturing

• Gathering data from different sources in digital form.
• Methods: keyboard, bar code readers, remote sensors.
• Heterogeneity among data sources can complicate data capturing.

Data Storage

• Storing captured data for later processing.
• Data is produced at a very high rate, making data storage challenging.
• Decreasing cost of digital storage devices simplifies the task.
• Data servers are deployed in large organizations for vast amounts of data.

Data Retrieval

• Fetching data from storage devices for processing.
• Minimizing data access time is crucial for faster data processing.

Data Deletion and Recovery

• A significant threat is data deletion due to device malfunction, accidental erasure, or malicious attacks.
• Deleting data typically involves marking the address entry as free rather than immediate removal.
• Data recovery retrieves deleted, corrupted, or lost data from secondary storage devices.
• Recovery is possible if the memory space has not been overwritten.
• Security concerns include unauthorized deletion or recovery of data.
• Mitigation strategies: limiting access, using passwords, encrypting files, using proper tools to delete/shred data before disposal of storage devices.

Software

• Software comprises the set of instructions that operate computer hardware.
• It is the non-physical component of a computer system.
• Software and hardware complete tasks together.
• Examples: operating systems, word processing tools, video players, photo editors.
• A document or image stored on a disk is a softcopy; once printed, it's a hardcopy.

Need of Software

• Software makes computer hardware useful and operational.
• It facilitates communication between hardware components and the end user.
• Software acts as an interface between users and hardware.
• Categories: System software, Programming tools, and Application software.

System Software

• Provides basic functionality to operate a computer by interacting directly with hardware.
• Examples: operating systems, system utilities, device drivers.

Operating System

• System software that operates the computer.
• Manages other application programs and provides access and security.
• Examples: Windows, Linux, Macintosh, Ubuntu, Fedora, Android, iOS.

System Utilities

• Software for maintenance and configuration of the computer system.
• Examples: disk defragmentation tool, formatting utility, system restore utility, anti-virus software.

Device Drivers

• Ensures proper functioning of a particular device.
• Acts as an interface between the device and the operating system.

Application Software

• Caters to different requirements of end-users and works on top of system software.
• Categories: general purpose and customized application software.

General Purpose Software

• Developed for generic applications to cater to a broad audience.
• Examples: spreadsheet tools, Adobe Photoshop, GIMP, Mozilla web browser, iTunes.

Customised Software

• Tailor-made software to meet specific requirements of an organization or individual.
• Examples: websites, school management software, accounting software.

Proprietary or Free and Open Source Software

• Free and Open Source Software (FOSS): Software freely available with source code for improvement.
  • Examples: Ubuntu, Python, Libreoffice, Openoffice, Mozilla Firefox.
• Freeware: Software freely available for use but source code may not be available.
  • Examples: Skype, Adobe Reader.
• Proprietary software: Software that must be purchased from the vendor with copyright.
  • Examples: Microsoft Windows, Tally, Quickheal.