What is a computer?

A computer is an electronic machine that accepts information (Data), processes it according to specific instructions, and provides the results as new information.

Monitor

Floppy Disk Drive

System Unit

Keyboard

CD-ROM / DVD-ROM

Drive

Mouse

Chapter:o1Computer overview

=> Computer: A computer is an electronic device that can perform a different types of operations in accordance with set of instructions is called program.

=> Data: Data are raw facts.

=>Information: Information is meaningful data.

=> Input-Process-Output(IPO Cycle) : Certain input is needed to accomplished a task , a process is carried out on the input to obtain the output.ÞFunctional Components of a computer:

In IPO Cycle, First stage is performed in computer by input unit, Second stage is performed by its central processing unit and the Third stage is performed by output unit.The main memory holds the input and intermediate output during the processing.

INPUT UNIT

MAIN MEMORY

CENTRAL PROCESSING UNIT

OUTPUT

=>INPUT UNIT: The input unit is performed by the input devices attached to the computer. Input unit is responsible for taking input and converting it into computer understandable form(the binary code).

EXAMPLES:KEYBOARD,MOUSE MICR, OMR, OCR, JOYSTICK.

=> Central Processing Unit: The CPU is the control Centre for a computer .it guides , directs, governs, its performance. It is brain of computer.

=> The CPU divided into two parts:

(a).Arithmetic Logic UNIT(ALU): The ALU performs all four arithmetical (+, -,*,/) and some logical operations(<, >,<=,>=,<>).

(B) CONTROL UNIT(CU): The CU control and guides the interpretation , flow and manipulation of all data and information. The CU sends control signals until the required operation are done properly by ALU and memory. It also responsible for execute the program. The CU gets program instruction from memory and executes the one after the other. After getting the instructions from memory in CU, the instruction is decoded and interpreted.

=>OUTPUT UNIT: The output unit is performed by the output devices attached to the computer. the output coming from CPU is in the form of electrical binary signals which needs conversion in some form which can be easily understood by human beings i.e. characters, graphical or audio visual.

Examples: Monitor, printer , plotter, speaker.

=> MEMORY: The memory is a device which can store the data and information.

=> MEMORY CELL: It is a device which can store a symbol selected from set of symbols.

bit

cell 0

cell 10 1 0 0 0 1 1 0

=> BYTE OR NIBBLE: A group of 8 bits is called byte and a group of 4 bits is know as nibble.

Unit Short Name Full Name

1 Bit Bit Binary Digit

8 Bits 1 Byte Byte

2 10 i.e. 1024 bytes 1 KB Kilo Byte

2 10 i.e. 1024 KB 1 MB Mega Byte

2 10 i.e. 1024 MB 1GB Giga Byte

2 10 i.e. 1024 GB 1TB Terra Byte

2 10 i.e. 1024 TB 1PB Peta Byte

2 10 i.e. 1024 PB 1EB Exa Byte

2 10 i.e. 1024 EB 1ZB Zetta Byte

2 10 i.e. 1024 ZB 1YB Yotta Byte

2 10 i.e. 1024 YB 1 BRONTO BYTE Bronto Byte

2 10 i.e. 1024 Bronto Bytes

1 GEOP BYTE Geop Byte

=> There are two types of memory

(a). Primary (Main ) Memory: It is also know as temporary Memory. Ram and Rom

(b). Secondary Memory: To store the data and information permanently. CD, Hard disk.

=> Hardware : The physical and tangible parts of the computer. i.e. The components that can seen and touched. Monitor ,mouse etc.

=> peripherals: The peripherals are devices that surround the system unit. Examples: keyboard, mouse, speaker, printer, monitor.

=> Software: The set of program that govern the operation of a computer system.

Types of SoftwareThere are two types of software1.System software2. Application Software System software: The software that controls internal computer operations is called system software system software Divided into two parts Operating system Language system.

Operating system(os): An operating system is a program which acts as an interface between a user and the hardware(i.e. all computer resources)Functions of operating system:

(i).It provide the instructions to prepare user interface.i.e, way to interact with user whether through typed commands or through graphical symbols.

(ii). Loads necessary programs (into the computer memory) which are required for proper compute functioning.

(iii). Coordinates how programs work with the CPU , keyboard, Mouse, Printer, and other Hardware as well as with other software

(iv). Manages way information is stored on and retrieved from disks

A set of software instructions that tells the computer what to do is called a computer program. Major Component of Computer System are:

TYPES OF OS:1.Single Program OS. As the name suggests , this OS is single user operating system , so only one user program can be supported and executed by it at any point.2.MultiProgram OS. It supports multiprogramming.i.e., more than one user can be supported by it, therefore ,more than one user programs are loaded and active in the main store at he same time.3.Time Sharing OS. This OS uses the time sharing technique. Each active user program is given a fair share of CPU time(δ),if the time elapses or an I/O operation is requested, CPU shifts over to the next jobs waiting and the previous program.4.Real Time os: The jobs have fixed deadlines and the jobs have to be completed within their deadlines. the system performance is measured by its ability to complete its jobs within specified deadlines. If a job cannot be complete within its deadline, its situation is called deadline overrun.5. Multiprocessing os: The Multiprocessing os is capable of handling more than one processors as the have to be executed on more than one processor(CPU)

Examples of operating systems are: Unix, Windows NT, Windows XP, MS-DOS, Linux, Solaris, VMS, OS/2 and System =>Language processors: It is a collection of program that convert high level language program into machine level language program.High-level language: A high-level language consists of instructions, or statements, that are closer to English and common mathematical notation. When programming in a high-level language, you do not have to concern yourself with the specific machine language of the CPU.

Assembler: It translates(converts) the assembly language program into an equivalent machine language program.

.

Interpreter: IT Converts a High level Language program into machine language by converting and executing it line by line. if there is any error in any line, it reports it at the same time and program execution cannot resume until the error is rectified.

Once a given instruction has been executed, then it translates and executes the next, and so on.

Compiler: It Translate(convert) the Entire HLL program into machine language program in one go, and reports all errors of the program along with the line numbers.

All instructions are compiled before any are executed by the CPU.

Application Software: It is a set of programs necessary to carry out operations for a specified application.=> Application software Categories into two types:

(a). Customized Application software : This type of software is tailor –made software according to a user’s requirements. The software is developed to meet all the requirements specified by the user.

(b). General Application software : This type of software is developed keeping in mind the general requirements for carrying out specific task

Þ Strength and Weakness of a computer:

=> Computer Strengths:

(i). Speed: Computer are much faster as compared to human beings. A computer can perform a task in a minute that may take day if performed manually.

(ii). High storage Capacity: Computers can store a large amount of information in very small space.

(iii). Accuracy: Computer s can perform all tha calculations and comparisons accurately provided the hardware does not malfunction.

(iv). Reliability: Computers can immune(protect) to tiredness and boredom or fatigue(mental exhaustion) .

(v). Versatility: Computers can perform repetitive jobs efficiently. They even can work in the area where human brain can err.

Þ Computer Weakness:

(i). Lack of Decision Making Power: Computer cannot decide on their own.

(ii). IQ Zero: Computers are dumb machines with zero IQ

=> FIRMWARE: It is prewritten program that is permanently stored in read only memory (ROM). It configures the computer and not easily modifiable by the user. Example: BIOS(BASIC INPUT OUTPUT SERVICE)

=> Liveware: The people associated with and benefited from the computer system.

The current classifications of computers place them into Three categories:

Analog Computer

Digital Computer

Hybrid Computers

Classification of Computers of On the basis of How It Functions

Digital Computers

Analog Computers

Classification of Computers of On the basis of How It Functions

• Operate on continuous data, like measuring temp. changes

• Faster• Accuracy of an analog

computer is restricted to the accuracy with which physical quantities can be sensed and displayed.

• Specific Purpose computers

• Digital computers work on discrete data.

• digital computer can process data with greater accuracy

• We generally use digital computers for business and scientific data processing.

Digital Computers

• Hybrid computers are computers that comprise features of analog computers and digital computers.

• The digital component normally serves as the controller and provides logical operations, while the analog component normally serves as a solver of differential equations.

Hybrid Computers

Þ Digital Computer classified into two typesÞ (i). Purpose –wiseÞ (ii). Size and Performance wiseÞ (i). Purpose –wise digital computer are

classified into two types.Þ (a). Special-purpose computer: It is designed

to performed a specific task. the instructions to carry out the task are permanently stored in the machine.

Þ (b). General-purpose computer: it can work on different types of programs input to it and be used in countless applications. The program are not permanently stored .

The current classifications of computers place them into five categories:

Embedded computer,,Microcomputers (Personal Computers)  Minicomputers, Mainframes, Super Computers,

Size and Speed Based Classification of digital

Computer Systems

=> Embedded computers: These computers are typically preprogrammed for a specific task, such as tuning to a particular television frequency. Examples: television, washing machine.etc.

PERSONAL COMPUTER The term microcomputer, also known as

personal computer (PC), or a computer that depends on a microprocessor. A microcomputer contains a central processing unit (CPU) on a microchip (the microprocessor), a memory system (read-only memory and random access memory), placed on a motherboard. Example:  desktop, notebook, laptop, handheld devices. Charcteristics:

developed in 1980 designed for single user not very powerful or expensive found in homes

Þ Micro computer also divided into three types

Þ PDA(Personal digital assistants)Þ Laptops and desktop personal

computer.Þ Workstations:• Between minicomputer and

microcomputer- in terms of processing power.

• Looks like PC and used by one person.

MINICOMPUTER

Another term rarely used anymore, minicomputers fall in between microcomputers (PCs) and mainframes (enterprise servers).

Minicomputers are normally referred to as mid-range servers now.   Characteristics:

      Smaller than mainframe      Can do several jobs at once      Can be used by many people at one time      Used by small companies

MAINFRAME In the early days of computing, mainframes were huge computers

that could fill an entire room or even a whole floor. As the size of computers has decreased while the power has

increased, the term mainframe has fallen out of use in favor of enterprise server. You'll still hear the term used, particularly in large companies to describe the huge machines processing millions of transactions every day.  

Characteristics:      Expensive     Powerful and fast     Is not limited to one job     Used by business and small government organizations

The main difference between a supercomputer and a mainframe is that a supercomputer channels all its power into executing a few programs as fast as possible, whereas a mainframe uses its power to execute many programs simultaneously.

SUPER COMPUTERThe fastest type of computer. Supercomputers are very expensive and are employed for

specialized applications that require immense amounts of mathematical calculations.

For example, weather forecasting requires a supercomputer.

Other uses of supercomputers include animated graphics, , nuclear energy research, and petroleum exploration.

Characteristics  Powerful

   Expensive   Dedicated to one purpose - weather, satellites, military    Used by large governments or very large companies   Can be used by thousands of people at the same time   Very large - fill rooms

Sixteen racks of IBM's Blue Gene/L supercomputer can perform 70.7

trillion calculations per second, making it the fastest machine known so far.

=>Input Device: A device used to provide data and instruction to the computer are called input device.

Example: keyboard

1.Keyboard: It is used to enter both numerical and characters type data. it is like a mechanical typewriter with alphanumeric and special keys.

=>Types of Keyboard

There are two type of keyboard

1.Serial keyboard

2.Parallel keyboard

=>A serial Keyboard is one which communicates the data to the central processing unit one bit a time. that is the bit pattern that forms a particular character is sent on a single wire.

ÞA parallel Keyboard carries one byte(8bits) at a time to the central processing unit. The bit pattern that forms a character is sent on 8 different wires.

Þ Standard Keyboard Layout :Þ A standard computer keyboard has about

100 keys.Þ Most keyboards use the QWERTY layout,

named for the first six keys in the top row of letters.

• The Keyboard - Standard Keyboard Layout

• Most keyboards have keys arranged in five groups:

• 1. Alphanumeric keys• 2. Numeric keypad• 3. Function keys• 4. Modifier keys• 5. Cursor-movement keys

•

ACADEMIC RECORDS

Password

ENTER Invalid Password

* * * * *

• Ergonomic Keyboards

• Long periods of keyboard use can cause injuries.

• An ergonomically correct keyboard can help you avoid injuries.

• You also can avoid injuries by adopting correct keyboarding practices.

• Mouse: It is small hand held pointing device connected to CPU through a cable.

The Mouse - Mouse Techniques

1.Pointing; Move the mouse to move the on-screen pointer.2.Clicking; Press and release the left mouse button

once.3. Double-clicking; Press and release the left

mousebutton twice.

4. Dragging; Hold down the left mouse button as youmove the pointer.

5. Right-clicking; Press and release the right mouse button.

Using the mouse involves five techniques:

=> Types of Mouse:

There are three types of mouse.

(i). Mechanical mouse: It has a rotating ball at bottom and has two click buttons on the top. As the mouse is moved across a rubber pad or a flat surface, the ball rolls and its movement is converted into electrical signal and communicated to CPU. these movements are interpreted and display on the screen as an arrow.

(ii). Opto- Mechanical mouse: It is same as Mechanical mouse but an opto Mechanical mouse: uses optical sensors to sense the motion of the ball

=> Optical Mouse: optical mouse have an optical sensor in place of a mouse ball. The optical mouse now a day use a laser to detect the mouse’s movement.

=> Wireless Mouse: Wireless or cordless are not physically connected to the computer .it uses either infrared or radio wave to communicate with computer.

Light Pen: It is a pencil shaped device. it is used to select screen coordinates by detecting the light coming from illuminated points on the CRT(cathode RAY Tube) screen. when an activated light pen, comes in contact with an illuminated spot on the screen. it generates an electrical signal which is taken as input to the system. then computer responds to it by displaying more information about the pointed item. it is useful in graphics program

Touch Screens: A type of display screen that has a touch-sensitive transparent panel covering the screen is known as touch screen.

Graphics Tablet: A graphic(digitizing) tablet is input device that enables to enter drawings and sketches into a computer. It consists of an electronic surface and a censor.

Digital Camera: A Camera that stores images digitally rather than recording them on film is called Digital camera. Once a picture has been taken, it can be downloaded to a computer.

Smart Card: The smart card contains a microprocessor that retains certain security and personal data in its memory at all times. The special reader machine that can read information on smart cards are called smart-card readers. It can hold more information, have some processing capability and are almost impossible to duplicate.

Joystick: It consists of a small rod(level or stick) mounted on a rolling ball. this rod is used to control the screen cursor. the movement of rod is converted into electric signals which are then sent to CPU for the subsequent processing. the CPU interprets these signals and displays the movement on the CRT screens.

Þ Microphone(MIC): It is used to record sound. It convert sound waves into audio signals and vice versa.

Þ Magnetic Ink Character Reader(MICR): Human readable characters are printed on documents(such as cheques) using a special magnetic ink. Special font has been set for these characters by American Banking Association. A magnetic ink character reader(MICR) reads these characters by examining their shapes ,using a 7*10 matrix.

Scanner: A Scanner is a device like photocopier, which creates an electronic form of printed image

The scanners can convert any image into electronic form by shining light on to the image and sensing the intensity of the reflection at every point.

Types of scanner Hand-held Scanner:

1.Less Expensive

2.Less wide

3.More passes per scan

4.More handyFlated Scanner:

1.More Expensive 2.Flat Surface

3.Single Pass per Scan 4.Higher Quality ImageDrum Scanner:

1.Medium Sized

2.Drum roles over Image for Scanning

Optical Character Reader(OCR): An optical Character reader is used to read character of special type font (or Fonts) printed on conventional paper with conventional ink. the printed characters are examined by passing them under a strong light and a lens system, which differentiates light (no ink) from inked areas, and a logical system which attempts to determine which of the possible characters is being examine.

Optical Mark Reader(OMR): Special Preprinted forms are designed with boxes which can be marked with a dark pencil or ink each box is distinctly so that the user clearly understands what response he is marking .such a document is read by a document reader,called optical mark reader.

objective 1.question 2.survey 3.time sheet

Bar Code Readers: A Bar Code is a pattern of printed bars on various types of products. It emits a beam of light which reflects off the bar code image. A light sensitive detector in the bar code reader then identifies the bar image by recognizing special bars at the both ends of the image. once the bar code is identified ,the car pattern is converted into numeric code.

Biometric: It is used for identifying a person’s identify, DNA identification, face – shape recognition ,signature verification.

=> Digital camera: A Camera that stores images digitally rather than recording them on film is called digital camera. Once a picture has been taken, it can be downloaded to a computer system, and then manipulated with a graphic program and printed.

=> Web camera: It is connected to a computer either directly or wirelessly. A webcam gathers a series of digital images that can be display remotely on web browsers remotely.

• Output Device: When the data and instructions are fed to the computer and processed, the next step is to get the output. This output may be displayed on the monitor or printed on the paper.

Softcopy output Hardcopy output.

=> Monitor: It is output device that display the information on the screen. The quality of pictures depends on the number of pixels that it can display.

=> Types of Monitors: There are two types of monitor.

1.Cathode Ray tube: The CRT works in the same way as a television. It contains an electron gun at the back of the glass tube.

2. Liquid Crystal Display(TFT):Thin film transistor is the device within each pixel that sets the charge .Printer: A printer is an output device which

is used to transfer output data from a computer onto paper.

Types of Printer There are two types of Printer

1.Impact Printer: There is mechanical contact between the print head and paper.

2.Non-Impact Printer: There is no mechanical contact between the print head and paper.

Impact Printer divided into Two parts.

1.Line Printer

2.Character Printer(Serial Printer)Line Printer prints a complete line at time Types of Line Printer There are two types of Line Printer Drum Printer: a drum printer consists of a

cylindrical drum on which characters are embossed.

Chain printer: A chain printer consists of a steel band on which the characters are embossed. To print a line, the characters in line are transmitted from the memory to printer buffer Character.

printers(Serial Printer): Serial character printer print one character at a time ,with the print head moving across a line

Serial Printer divided into Two Parts.

1.Dot Matrix Printers: The printing head contains a vertical array of pins. As the head moves across the paper, selected pins free against an inked ribbon to form a pattern of dots on the paper.

2. Letter Quality Printers: The letter quality printers print full characters (continuous character not as the character mode of dots)

Non-Impact Printers: The limitations of speed in electromechanical device and cost considerations have led to the development of printers called non-impact printers.

Type of Non-Impact Printers1.Electromagnetic printers: A

magnetic image can be written on a drum surface. then this surface is passed through magnetic powder which adheres to charged areas.

The powder is pressed onto the paper.

2.Thermal Printers: An electric pulse can be converted to heat on selected sections of a printing head or on wires or nibs(heads). When this head is applied to head sensitive paper, a character is printed.

3. Electrostatic printers:4. Inkjet printers: It is a character printers,

which form characters and all kinds of images by spraying

small drops of ink on to the paper. The print head of an inkjet printer contains up to 64 tiny nozzles.

Laser printer: Laser printers are page printers, which print one page at a time. The main components of a laser printer are a laser beam source, a multi-sided mirror, a photoconductive drum and toner.

1.High speed 2.High quality output.1.Cost. 2.maintenance cost is high.

Plotters: It is a output device to produce graphical output .that is used in architects, engineers, city planners etc.

Types of Plotters 1.Drum plotter 2. Flat Bed plotter. Visual Display Unit(VDU): A

monitor(the screen) is a box consisting of a CRT(cathode ray tube) and its power supply.

Speakers: Enhances the value of educational and presentation products. Speakers receive the sound in the form of electric current from sound card and then convert it to sound format.

Bit : A bits is a binary digit either a 0 or 1. Byte: A byte is a basic unit of memory A sequence of 8 bits. Word: A sequence of 16 bits or 2 bytes.

63

Memory• Essential component of computer, stores data, programs and

results.• Three kinds of memory in modern computers:

1.Semiconductor 2.Magnetic 3.Optical memories• Types of memories

1.Main memory 2.Secondary (Auxiliary) memory

ROM Memory

Static Memory

Memory

RAM Memory

Primary (Main) Memory(Immediate access store(IAS))

Masked ROM

Auxiliary (Secondary) Memory

DynamicMemory

PROM EROM EEROM

SemiconductorMemory

Magnetic Optical

RAMROM

HARDDISK

FLOPPYDISK

TAPE

CD-ROM

WORM

Memory: Memory is a device where data and instructions are Stored and retrieve.

Types of Memory

1.Main memory(Immediate access store(IAS))

2.Secondary memoryMain memory: It is the place where the data

and instructions supplied by the input devices are stored.

It is a temporary because the data and instructions stored are eased when power cut off.

Primary memory is divided into a number of memory cells (bits) or bytes.

A bit (binary digit) is the smallest storage unit within a computer. It is a tiny electrical circuit that can be in one of two states:

A voltage high represented by the symbol 1

A voltage low represented by the symbol 0

Any system of symbols can be represented by bit or byte patterns.

Each byte has a unique integer address and it is usually 8 bits.

Types of Main memoryThere are two types of main

memory.1.RAM(random Access Memory)2.ROM(Read Only Memory) RAM: It is the read and write

memory. It is like a page notebook, where write something to or read something from.

Any memory location is accessed randomly for reading and writing.

It is a temporary because the data and instructions stored are eased when power Failure.

It is also known as Volatile Memory. It is Two Types 1.Static 2.DynamicBoth are volatile

RAM• Dynamic RAM made from MOS.

Charge must be continually refreshed in order to maintain data. However, it is cheaper, more compact than Static RAM.

• Dynamic Ram used for most primary memory. Amount of data per chip has increased rapidly.

RAM• Static RAM is expensive, but does not

need to be refreshed, and is faster. Much smaller data capacity on a chip (~256 k).

• Generally made using bipolar technology, although recently have developed MOS static RAM.

• SRAM is often used for cache memory, because of its faster access time

Rom: It is a permanent memory. The data is stored permanently and cannot be altered by the programmer. It is also known as Field Stores or Dead Stores.

Types of ROM1.PROM(Programmable Read-Only Memory): It is

initially empty. Later, the user can store programs ,data or any other information permanently. However, these programs cannot be erased once they are written to it.

2.EPROM(Erasable Programmable Read-Only Memory): The Contents stored in this can be erased by exposing it to ultra violet light source for about 10-20 minutes.

then it is progammed,that is new information can be stored.

3.EEPROM(Electrically Erasable Programmable Read-Only Memory): The contents stored in this can be erased electrically. Later new information is stored in it.

It is also known as Flash Memory.

• DifferencesRAM holds the programs and data that the processor is actively working with.

ROM contains software that is used in Input/Output operations. It also contains software that loads the Operating System in Primary Memory.

The CPU can read and write to RAM but it can only read from ROM.

RAM is volatile while ROM is not.

Primary MemoryUNIT SYMBO

LPOWER OF 2

Number of bytes

Byte 02

1

Kilobyte KB 102

1,024

Megabyte

MB 202

1,048,576

Gigabyte GB 302

1,073,741,824

Terabyte TB 402

1,099,511,627,776

Primary and Secondary Memory Comparison

Primary memory Secondary memory

Fast Expensive Low capacity Connects directly to

the processor

Slow Cheap Large capacity Not connected

directly to the processor

76

Memory• The diagrams shown below represents the memory hierarchies as

per the speed of operation.

CPU

PrimaryMemory

SecondaryMemory

CacheMEM

PrimaryMemory

SecondaryMemory

CPU

Cache Memory: It is a high speed memory and placed between the CPU and the main memory.

=>Users cannot access this memory. it stores data and instructions that are currently to be executed.

=>Cache memory contains a copy of frequently used data/programs from main memory (ie it duplicates some contents). When the CPU attempts to read a word of memory , a cache controller checks to determine if the word is in cache.

=>If present then word delivered to CPU (called a hit); else (a miss) gets block from main memory and loads it into cache, preserving locality of execution.

=>Hit ratio is hits to total requests

Memory hierarchy enhancements• Caching and virtual memory are both used to

improve cost/benefit performance of the memory hierarchy.

• Caching improves memory access speed to both primary and secondary storage by predicting next required instructions/data & storing it in faster memory (higher up hierarchy).

• Virtual memory increases primary memory capacity while decreasing cost by using secondary memory as though it was RAM (further down hierarchy)

Secondary Memory: secondary storage devices are used to store large amount of data permanently for long-term .

Types1.Floppy Disks2.Hard Disks 3.Magnetic tapes 4.Magnetic drum 5.CD-ROM

• Hard Disk: This is a high capacity storage device ranging from 1GB to Tera Bytes .

• Concentric circles on the magnetized surface of the magnetic disks are known as Tracks.

Each track is dived into 8 parts. Each of the 8 parts of a track is called a

Sector.Sectors: The Tracks on the disk surface are

divided into invisible segments known as sectors.

Cylinder: Similar numbered tracks on different platters of a hard disk form a cylinder.

Hard Disk Example

Locating a Block of DataSeek Time Latency Time Transfer Rate

Desiredtrack

Seek

Head

TransferLatency

Note: Access time = seek time + latency

Hard Disk Layout

Platter

Track

Cylinder

Drivemotor

Headmotor

Head, onmoving arm

Block

Sector

Track

Head

Head assembly

Magnetic Disks

• A magnetic substance is coated on a round surface

• The magnetic substance can be polarized in one of two directions with an electromagnet (“writing data”)

• The electromagnet can also sense the direction of magnetic polarization (“reading data”)

• Similar to a read/write head on a tape recorder (except the information is digital rather than analogue)

Floppy Disks

• Also called “flexible disks” or “diskettes”• The platter is “floppy”, or flexible (e.g.,

mylar)• Most floppy disk drives can hold one

diskette (two surfaces)• The diskette is removable• Typical rpm: 300, 360• Capacities: 700 KB to 1.4 MB (& up to 100

MB “zip” disks)

Floppy Disk Example

Writeprotect tab

Spindle

ShutterAccess window

Cutawayshowing disk

Case

Digital Video Disk or Digital Versatile Disk(DVD): DVD is a optical storage device .It store more information and transfer it to the computer very fast as a CD-ROM.

DVDs come in two Formats: 1.DVD-Video Format 2.DVD_ROM Format. Blue Ray Disk(BD): It use a blue –violet

laser(450nm) is that it has a shorter wavelength than a red laser(650 nm) , which makes it possible to focus the laser spot with even greater precision. It storage capacity 25 GB/50GB.

• Communication Bus: In computer architecture, a bus is a system that transfers data between computer components or between computers

• Address Bus (16 lines): This is a system of bus, which is used to specify the address of a memory location. The width of a bus determines the number of memory locations that can be addressed..

• Data Bus (8 lines): It carries data in binary form, between the processor and other external units.

• Control Bus: These have specific functions for coordinating and controlling microprocessor operations.

Ports: It is used to connect external devices to the computer.

• Serial Ports: Through this port the information travels in and out one bit at a time. Serial ports come in the form of 9-pin or 25-pin male.

Parallel Ports. It can receive or send a byte at a time.

USB Ports. AGP Ports. Connect to graphic card.

Infrared Ports. It sends or receive infrared • Signals from other devices.BlueTOOTH. It describes how mobile

phones and PDA can connected through short range wireless connection.

Network Ports. It are used to enabled

Communications Between programs.Phone Ports. It is a port that allows

connecting telephone equipment with the computer sound card.

MEMORY CARDS

A memory card is a small storage medium used to store data

For use on small computing devices.

Smart media cardExtreme media card

Multimedia cardSecure digital card

Compact flash cardsMemory stick

Networks and the InternetThe world’s largest

network is the Internet

Most users connect to the Internet in one of two ways:Internet service

providerOnline service

provider

The World Wide WebOne of the more popular segments of the

Internet is the World Wide Web, also called the Web.

A Web page is a document that contains text, graphics, sound, and/or video and has built-in connections, or hyperlinks to other Web documents

A Web site is a related collection of Web pagesYou access and view Web pages using a

software program called a Web browserA Web page has a unique address, called a

Uniform Resource Locator (URL)A hyperlink is a virtual connection to another

place on the Web

THE END

Hard Disks• The platter is “hard” (e.g., aluminum)• Most hard disk drives contain more than one

platter• On most hard disk drives, the disks are

“fixed” (i.e., not removable)• On some hard disk drives, the disks are in a

removable pack (hence, “disk pack”)• Typical speed of rotation: 3600, 5400, 7200

rpm (rpm = “revolutions per minute”)• Capacities: 500 MB to 1+ TB (terabyte = 240

bytes)

Winchester Disks

– Invented by IBM– A type of hard disk drive– The disk is contained within a sealed unit– No dust particles– When powered off, the head is “parked” at the outer

edge of the platter and rests on the platter surface– When powered on, the aerodynamics of the head and

enclosure create a cushion of air between the head and the disk surface

– The head floats above the surface (very close!) and does not touch the surface

– Thus, “head crash” (the head touches the surface, with damage resulting)

Terminology– Platter

• A round surface – the disk – containing a magnetic coating

– Track• A circle on the disk surface on which data are contained

– Head• A transducer attached to an arm for writing/reading data

to/from the disk surface– Head assembly

• A mechanical unit holding the heads and arms• All the head/arm units move together, via the head

assembly– Cylinder

• A set of tracks simultaneously accessible from the heads on the head assembly

Terminology• Drive motor

– The motor that rotates the platters– Typically a DC motor (DC = direct current)– The disk rotates at a fixed speed (e.g., 3600 rpm,

revolutions per minute)

• Head motion– A mechanism is required to move the head assembly

in/out– Two possibilities:

• A stepper motor (digital, head moves in steps, no feedback)

• A servo motor (analogue, very precision positioning, but requires feedback)

Terminology– Sector

• That portion of a track falling along a predefined pie-shaped portion of the disk surface

• The number of bytes stored in a sector is the same, regardless of where the sector is located; thus, the density of bits is greater for sectors near the centre of the disk

• The rotational speed is constant; i.e., constant angular velocity

• Thus, the transfer rate is the same for inner sectors and outer sectors

– Block• The smallest unit of data that can be written or read

to/from the disk (typically 512 bytes)