Computer System Overview

Introduction to Computer Systems

• Computers are machines that have revolutionized the world.

• The way people lived around $25-30\,\text{years}$ ago is significantly different from today due to the ubiquity of computer technology.

• Modern life for a student involves constant interaction with email, the Internet, printouts, music, and smartphones.

• Computers play a direct or indirect role in every aspect of life, accomplishing tasks diligently and efficiently through the combination of hardware and software.

• NOTE: A computer runs on electricity power.

Hardware and Software Definitions

• Hardware: The physical electronic components of a computer are called hardware.

  • Examples include: keyboard, $CPU$, monitor, printer, etc.

• Software: The recorded instructions and programs that govern the working of a computer.

• Program: A set of instructions used to carry out a specific task or achieve a special work goal.

Computer Components and Basic Organization

• A computer system comprises of $5$ basic components (as per Fig. 1.1):

  • (i) Input Unit: Responsible for taking input for the computer. It is made of the input devices attached to the computer system.

  • (ii) Output Unit: Responsible for producing information as output. It is made of the output devices attached to the computer system.

  • (iii) Central Processing Unit ($CPU$): Responsible for processing data and instructions. It comprises two parts: the Arithmetic and Logic Unit ($ALU$) and the Control Unit.

  • (iv) Primary Memory: The internal volatile memory where data and instructions are stored during processing.

  • (v) Secondary Storage Unit: Refers to external storage devices that provide permanent memory to the computer system.

• Computer Organisation Definition: The logical structure of a computer system that defines how components are connected, how they affect one another's functioning, and how they contribute to overall performance.

• IPO Principle: Computers follow the $Input \rightarrow Process \rightarrow Output$ principle where input is processed to generate specific output.

• Interconnections: Functional components like the $CPU$, $ALU$, Registers, Control Unit, and Memory are linked to the Input unit, Output unit, and Storage unit through a system known as the BUS (as shown in Fig. 1.2).

The Input Unit and Common Devices

• The input unit consists of various input devices that take input in different forms and pass them in digital form to the $CPU$.

• Main Task: Taking input and converting it into a computer-understandable form, specifically binary code.

• Content of Input: Consists of both data (on which action is performed) and the instruction (the action to be taken).

• Common Input Devices:

  • Keyboard: A typewriter-like device used to type letters, digits, and commands. Braille keyboards are available for visually challenged people.

  • Mouse: A pointing device with either a roller on its base or a laser mechanism. it controls the movement of the mouse pointer on the screen.

  • Microphone ($Mic$): Used to send sound input. It converts sound into digitized sound or digital audio. A mic requires special hardware known as a sound card to function.

  • Other Devices: Magnetic Ink Character Reader ($MICR$), Optical Mark Reader ($OMR$), Optical Character Reader ($OCR$), and joystick.

The Output Unit and Common Devices

• The output unit converts electronic binary signals from the $CPU$ into human-readable forms such as characters, graphical displays, or audio-visual content.

• Common Output Devices:

  • Monitors: Also known as the screen, it is the most common output device. It displays information similarly to a television. The picture is made of thousands of tiny colored dots called pixels. Braille monitors are available for visually challenged users.

  • Printers: Deliver information by printing characters on paper. Varieties include inkjet, laserjet, and dot-matrix printers. $3D\,\text{printers}$ are currently available to create/print $3D$ models.

  • Speakers: Receive sound in the form of electric current from the sound card and convert it into audible sound.

The Central Processing Unit (CPU) and its Sub-components

• The $CPU$ is the main control center and processing unit, often called the brain of the computer. It guides, directs, controls, and governs the performance of the computer.

• Sub-components of the $CPU$:

  • Arithmetic Logic Unit ($ALU$): Performs four arithmetic operations ($+$, $-$, $\times$, $\div$) and logical operations (<, >, =, \le, \ge, \neq). When numbers are compared or added, they are sent from memory to the $ALU$, and the result is returned to memory. Logical operation results are either $TRUE$ or $FALSE$, providing decision-making capabilities.

  • Control Unit ($CU$): Acts as a supervisor by controlling and guiding all operations. It guides the interpretation, flow, and manipulation of data and information. It sends control signals to ensure the $ALU$ and memory perform correctly. It is also responsible for program execution, fetching instructions from memory, decoding them, and executing them.

  • Registers: Also called processor registers, these are small units of data holding places used to temporarily hold important processing information, such as data parts, memory addresses, or specific instructions, while processing occurs.

Microcontrollers and Embedded CPUs

• Modern smart machines like washing machines and microwave ovens contain embedded $CPUs$.

• Microcontrollers: These consist of embedded $CPUs$ with accompanying memory ($ROM$ and $RAM$) and embedded instructions within internal circuitry.

Functional Workings of Main Memory (Primary Memory)

• Main memory is the internal workspace of the computer where data and instructions are held during processing.

• Each memory location possesses a unique memory address.

• Operation: Once a task is completed, the memory is cleared so the space is available for the next task.

• Volatility: Primary memory is temporary; when power is switched off, everything stored gets erased and cannot be recalled.

Units of Computer Memory Measurement

• Bit (Binary Digit): The elementary unit of memory.

• Nibble: A group of $4\,\text{bits}$.

• Byte: A group of $8\,\text{bits}$. It is the smallest unit that can represent a data item or character.

• Rule of Thumb: Every higher memory unit is equal to $2^{10}$ (which is $1024$) of its lower unit.

• Common Memory Units:

  • $1\,\text{KB}$ (Kilo Byte) = $1024\,\text{Bytes}$

  • $1\,\text{MB}$ (Mega Byte) = $1024\,\text{KB}$

  • $1\,\text{GB}$ (Giga Byte) = $1024\,\text{MB}$

  • $1\,\text{TB}$ (Terra Byte) = $1024\,\text{GB}$

  • $1\,\text{PB}$ (Peta Byte) = $1024\,\text{TB}$

  • $1\,\text{EB}$ (Exa Byte) = $1024\,\text{PB}$

  • $1\,\text{ZB}$ (Zetta Byte) = $1024\,\text{EB}$

  • $1\,\text{YB}$ (Yotta Byte) = $1024\,\text{ZB}$

Primary Memory Types: RAM and ROM

• Random-Access Memory ($RAM$):

  • Allows information transfer from any desired random location.

  • Volatile: Contents are erased when power goes off.

  • Dynamic $RAM$ ($DRAM$): Composed of transistors and capacitors. Access times range from below $20\,\text{to}\,70\,\text{nanoseconds}$.

  • Static $RAM$ ($SRAM$): Composed of flip-flops (binary cells storing one bit). Faster than $DRAM$ ($\approx 10\,\text{nanoseconds}$). Used in specialized applications.

• Memory Access Time: The amount of time taken to produce data required from memory, from the start of access until the availability of data.

• Read Only Memory ($ROM$):

  • Performs read operations only; no write capability.

  • Non-volatile: Information is permanent and cannot be altered.

  • ROM Types:

    • $PROM$ (Programmable $ROM$): Also called $OTP$ (One Time Programmable). Requires special equipment called a $ROM\,\text{burner}$.

    • $EPROM$ (Erasable Programmable $ROM$): Can be erased using $UV\,\text{radiation}$ ($20\,\text{minutes}$) and reprogrammed.

    • $EEPROM$ (Electrically Erasable Programmable $ROM$): Erased electrically, which is faster. Allows selective byte erasure.

    • Flash $EEPROM$: Extremely fast erasure (entire contents in less than $1\,\text{second}$). Erases fully, not selectively.

    • Mask $ROM$: Programmed by the $IC$ manufacturer; not user-programmable.

Understanding Cache Memory

• Definition: A special high-speed storage mechanism, which can be a section of main memory or an independent high-speed device on the $CPU$ chip.

• Function: The $CPU$ looks in the cache first for data. If found, it bypasses main memory access, making the process very fast.

• Cache Hit: When data is successfully found in the cache.

• Hit Rate: The effectiveness measure of a cache. The processor accesses information from the cache $95\% \,\text{of the time}$ it is working.

Secondary Storage Units and Media

• Storage is necessary because primary memory is limited and temporary.

• Magnetic Media:

  • Hard Disks: Store information on spinning circular platters coated with magnetic material. Data is recorded as tiny magnetic spots by magnetic heads. Capacity ranges from $GB$ to $TB$.

• Optical Media:

  • Compact Disks ($CDs$): Capacity up to $700\,\text{Mb}$. Relative cheapness.

  • DVDs: Also called Super Density disk ($SD$). Capacity up to $17\,\text{gigabytes}$ ($4\,\text{hours}$ of movies). Transfers data $20\,\text{times}$ faster and holds $15\,\text{times}$ more information than a $CD$.

  • Blu Ray Disk ($BD$): Uses a blue-violet laser ($405\,\text{nm}$) instead of a red laser ($650\,\text{nm}$). The shorter wavelength allows for higher precision and tighter data packing. Capacity up to $128\,\text{GB}$.

• Flash Memory:

  • Small, ultra-portable storage with no moving parts (solid state). Retains data without power. Sizes range from $256\,\text{Mbytes}$ up to $128\,\text{GB}$ and beyond.

The System Bus and Its Types

• The system bus is an electronic pathway of connecting cables that links major computer components to pass data and instructions.

• Data Bus: The data-carrying part of the system bus.

• Control Bus: The part that carries control instructions.

• Address Bus: The part that carries memory addresses.

• $I/O\,\text{Bus}$: Connects input, output, and other external devices to the system.

Mobile System Organization and Architecture

• Mobile systems are effectively tiny computers. They have less computing power than full versions and run on limited battery power.

• System on a Chip ($SoC$): Major components integrated on a single chip to consume less power.

• Mobile Processor ($Mobile\,CPU$): The brain of a smartphone. Subdivided into:

  • Communications Processing Unit: Responsible for phone calls. Uses a digital signal processor to work with the $RF\,\text{Transceiver}$ and Audio subsystem.

  • Radio Signal Management Unit: Connects the $SIM$ (modem type) to base stations through radio signals ($3G/LTE/4G$ based cellular networks).

  • Applications Processing Unit ($APU$): Governs all operations by running mobile applications ($apps$).

Functional Components of a Mobile System

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

• Camera Subsystem: Features an integrated Image Signal Processor ($ISP$) for instant capture, high resolution, and image stabilization.

• Mobile System Memory:

  • $RAM$ (Random Access Memory): Work memory where apps load to execute. More $RAM$ yields better performance. Volatile.

  • $ROM$ (Read Only Memory): Technically Flash memory or $EEPROM$. Part of internal storage, not writable by users.

• External Storage: Also called expandable storage. Includes $SD$ cards, micro $SD$ cards, and cloud storage.

• Power Management Subsystem: Provides power through a battery unit, charger management system, and battery charger.

Types of Computer Software

• Hardware: Tangible physical components (Input/Output devices, $CPU$, disks, etc.).

• Software: Set of programs that govern operations and make hardware run.

• Hierarchy: Hardware is supervised by the Operating System, which is supported by Language processors and Utilities. Application software (like Spreadsheets and Databases) sits at the top for users.

System Software and Operating Systems

• System Software: Software that controls internal operations (reading data, transmission, component checks, and binary conversion).

• Operating System ($OS$):

  • Primary goal: Make the computer convenient to use.

  • Secondary goal: Use hardware efficiently.

  • Function: Acts as an interface between user and hardware. Loaded into $RAM$ during boot-up.

  • Major Components: Hardware, $OS$, Application program routines (compilers, DBMS, utilities), and Humanware (users).

  • Types: Single user, Multiuser, Time sharing, Real time, Multiprocessing, Distributed, etc.

Language Processors and Translators

• Language Processor: Translates source code into object code (machine code).

  • Source Code: Program code written in high-level programming languages ($HLL$) like C, Java, or C++.

  • Object Code: Machine language or binary code understandable by hardware.

• Three Types of Language Processors:

  • (i) Assembler: Converts assembly language into machine language.

  • (ii) Interpreter: Translates and executes instructions line-by-line.

  • (iii) Compiler: Translates and executes the entire program in one go. Results in faster execution time because no further conversion is needed at runtime.

Application Software, Packages, and Utilities

• Application Software: Programs used to carry out specific tasks (railway reservation, inventory, billing, etc.).

• Packages: General-application software meant for many users. Categories include:

  • Word Processing Software

  • Spreadsheets

  • Database Management Systems ($DBMS$)

  • Desktop Publishing Software ($DTP$)

  • Graphics, multimedia, and presentation apps.

• Utilities (Housekeeping programs):

  • Text Editor: For creating and editing files.

  • Backup Utility: Duplicating information to protect against data loss.

  • Compression Utility: Compressing large files to save storage.

  • Disk Defragmentor: Rearranges fragmented files (stored at different locations) so they are stored in contiguous units, consolidating free space.

  • Antivirus Software: Scans and removes malicious programs (viruses). Some remain in memory to detect viruses as they occur.

Specialized Business Software

• Created specifically according to business requirements.

• Readymade examples: Inventory Management System, Payroll System, Financial Accounting.

• Customised (tailor-made) Software: Specific requirements for a single company; usually cannot be directly installed at another workplace with different needs.

Software Libraries in Programming

• Software Library: A predefined suite of data and programming code (functions, scripts, classes) available for developing new programs.

• Developers import/include these libraries to use complex functionality without rewriting it from scratch.

• Python Software Libraries:

  • 1. $NumPy$ (Numerical Python): Provides features for numeric arrays and matrices.

  • 2. $SciPy$ (Scientific Python): Modules for linear algebra, optimization, integration, and statistics.

  • 3. $Pandas$ Library: For manipulation, aggregation, and visualization of labeled and relational data.