COMPUTER

 COMPUTER

TABLE OF CONTENT

• What is a computer?

• System of components

• Types of computer

• Input data

• Output data

• Central processing unit

• Ram 

• Rom

• organization of computer system

• Input device

• Types of input device

• devices  used  in  this  category  are:-

• (a)Video  digitiser

• (b)Digital  camera

• (c)Scanning  devices

• (d)Voice  input

• (e)Remote  control

• (f)Magnetic  stripe  reader

• (g)Sound sensor–microphone

• (h)MIDI  instrument.

• Memory or storage device

• Types of memory

• RAM

• ROM

• Types of RAM

• Types of ROM

• Output device

• printer

A computer  is  basically  a  device that  can  respond  to  a  specific  set of instructions  in  a  well defined manner,  execute  a  pre recorded list of instructions (a program)and quickly store and retrieve  large amounts  of  data. Since Computer  is  understood  more  by  its functions  than  its  appearance,  let  us  see  what  functions  each  of the  components  performs

The electronic  computer  has  been  around  for over  half  a  century,  but  its  ancestors  have  been around  for  2000  years.  However,  only  in  the  last 40  years  has  it  changed  society.  From  the  first wooden   abacus   to  the latest high-speed microprocessor,  the  computer  has  changed  nearly every  aspect  of  our  lives  for  the  better.

Computer  indeed  derives its  name  from  its  essential function,namely, to compute.In  a  rudimentary  sense  any Computation requires primary  data  and  operations performed  between  them.  This  would  mean  receiving  data,  processing them,  keeping  in  memory  the  data  at  different  stages  of  operation,having  some  set  of  data  that  is  fundamental  to  all  operations  and giving  outcomes  of  operations.

Hence,  essentially  a computer means  a system  of  components :- 

(i)  to  input  data  and  display  output  i.e.  Inputand  Output  devices; 

(ii)  processing  unit  called  the  Central  Processing Unit (CPU) and

 (iii) the Memory space which can be Read Only Memory(ROM)  or  Random  Access  Memory  (RAM). 

 One  should  realise  that  it  is not  the  external  appearance  by  which  a  computer  is  understood as much  as  its  functionalities. In fact, the memory in terms of capacity (space) and speed, and the processing  capacity  of  the  CPU  (speed  with  which  it  processes) characterize computers and distinguish them. Also the manner in which data  is  presented  determines  a  classification  of  computers,  namely, analogue  or  digital computers.

Computers can be classified into two major types based on their way of

handling  data.  These  are  as  follows:-

1.Analogue Computers: They work on continuous variables like waves of  the  signal,  their  amplitude,  etc.

2.Digital Computers:They work on the principle of binary digits i.e.0 and 1. 

Any value or symbol is represented through a binary value.

Digital computers  can  also  be  classified  according  to  their  physical structure (size) and the purpose of their use. Based on capacity, speed and  reliability  they  are  classified  into  three  categories:-

I. Microcomputer: The  term  “Microcomputer”  was  introduced  with

the  advent  of  single  chip  large  scale  integrated  circuit  (LSIC)  computer processors.  It  is  the  smallest  single  user  computer  and  its  CPU  is a microprocessor.  It  can perform  the  same  operations  and  can  use  the same  type  of  instructions  as  other  computers.  These  are  the  most frequently  used  computers,  better  known  by  the  name "personal computer".

in our  everyday  use,  the  term  “computer”  refers  to digital  computers,  a  typical  example  being  the common  personal  computer  (PC).  These  can  be classified  mainly  as  Desktop  Computers,  Laptop Computers,  Palmtop  Computers,  Personal  Digital Assistant  (PDA),  Tablet  PC,  etc.

Desktop  Computers

           

Desktop computers are larger and not meant to be portable. They usually sit in one place on a desk or table  and  are  plugged  into  a  wall  outlet  for  power.

The  case  (chasis)  of  the  computer  holds  the  CPU.When  this  case  lies  flat  on  the  desk  then  it  is generally  referred  to  as  a Desktop  Model  else  when    it  stands  vertically  on  the desk  in  the  form  of  a  tower,  it  is referred  to  as  a Tower  Model.  The  computer  usually has  a  separate  monitor.  A  separate  keyboard  and

the mouse allows the user to input data and commands.The  main  advantage  of  tower  models  is  that  there are  fewer  space  constraints,  which  makes installation  of  additional  storage devices earlier.

Laptop

This  is  a  small,  portable  computer,

small  enough  that  it  can  sit  on  the  lap.  Nowadays laptop  computers  are  also Called notebook computers.

       

Hand-held  Computers/Palmtop

This  computer  is  smaller  than  a  laptop.  It  is  so small that it literally fits in a palm, hence, referred to  as  palmtop. Because  of  their  small size,  most  palmtop  computers  do  not  Include disc drive. Compared  to  full-size  computers,  palmtops are  severely  limited,  but  they  are  practical  for certain  functions  such  as  phone books  and calendars.  Sometimes  these  are  also  called  pocket computers.

Personal  Digital Computers/Assistants

Palmtops  that  use  a  pen  rather  than  a  keyboard for input are often called PDAs. This isa  hand–held  device  that  combines  computing, telephone  fax  and  networking  features.  PDA  can function  as  a  cellular  phone,  fax  sender  and personal  organizer.  PDA  was  pioneered  by  Apple,which introduced the Newton Message Pad in 1993.

Tablet  PC

It  is  a  notebook  slate-shaped  mobile  computer which  is  equipped  with  a  touch screen or  graphics  table  which  allows  the  user  to  operate the  computer  with  a  digital  pen  or  stylus  or fingertip.  A  wireless  keyboard  can  be  connected to     this     forextensive  textinput.  Other  models  of  tablet  PCsare  convertible  model  (screen  can rotate over the keyboard) and hybrid model  where  the  screen  is  fixed  on the  keyboard.

Workstation

A  powerful,  single  user  computer,  a

workstation  is  like  a personal computer,  but  it  has  a  more powerful  microprocessor  and  in  general, a higher  quality  monitor  used  in  computer  aided  design  and  other applications  requiring  a  high  end,  usually  expensive,  machine  with considerable  calculating  or  graphics capability.

II.  Mini  Computer: It  is  a  multiuser  computer  capable  of  supporting up to hundreds of users simultaneously. They are usually more powerful compared  to microcomputers.  Minicomputers  are  also  known  as  midrange  computers  as  their  cost  and  computing  powers  lie  in  the  middle range  between  micro  and  mainframe  computers.  Mini Computers are used  for  multi users  and  interactive  applications.

III. Mainframe  Computer: A  powerful  multi user  computer,  the mainframe  computer,  is  capable  of  supporting  many  hundreds  or thousands of users simultaneously. They are capable of faster processing and  greater  storage  area.  They  are  used  in  research  organizations,large industries, large businesses and government organizations, banksand  airline  reservations  where  a  large database is required.

ORGANIZATION OF THE COMPUTER SYSTEM

A computer  system  is  usually  defined  as  a  combination  of hardware  and  software.  Computer  hardware  is  the  physical  equipment.

Software  is  the  collection  of  programs  that  make  the  hardware  do  its  job. Each  of  the  hardware  and  software  components  has  undergone refinements and modifications depending upon the limitations encountered by  the  users  and  the  endeavors  to  overcome  these  limitations  to  meet new  requirements  and  challenges.  Let  us  therefore  understand  the computer  from  two  perspectives,  namely,  the  general  functions  of  its components  and  the  evolution  these  components 

have undergone.

HARDWARE

In order to accomplish a particular task the computer performs a series of jobs, namely, Input, Storage, Processing and Output, which it handles in  a  very  special  way  as follows:-

It  accepts  the  data  (input)  from  the  user.

• The  computer  has  memory  chips,  which  are  designed  to  hold  data until  it  is  needed.

•  It processes this data into information. The computer has an electronic brain  called  the  Central  Processing  Unit,  which  is  responsible  for processing  all  data into  information according  to  the  instructions given  to  the  computer.

• It  then  returns  the  processed  information  (output)  to  the  user.

For  performing  each  of  the  jobs  listed  above,  every  computer  has

special  parts/components,  for  Input  Device,  Storage  Device,  Central

Processing  Unit  and  Output device.

INPUT DEVICES

General FunctionsIt  provides  a  means  for  the  machine  to  communicate  with  its  external environment  by  accepting  (or  reading)  data  and  the  program.

1.It converts the data based on the program into computer acceptable

form  through  an  input  interface.

2.It  supplies  the  converted  instructions  and  data  to  the  computer system  for  further  processing.

The  very  scope  of  computers  is  enough  to  understand  that  there  is

no limit to the form and type of data that serves as an input.

Sometimes the  input  is  in  the  form  of  text  in  normal  language,  sometimes  it  is  a picture,  sometimes  it  is  a  voice  input  like  a  song.  Selection  of  an appropriate  input  devices  will  improve  efficiency  and  keep  human interaction minimal.

Types of Input Devices

On-line  or  Direct  Data  Entry  Devices:- These  devices  are  under  the control  of  the  CPU  and  communicate  directly  with  the  CPU,  that  is, these  are  connected  via  cable  to  the  CPU.  This  process  of  data  entry may be time consuming and may have errors but by using these devices, we can avoid having to capture data from paper.

These are also known as Interactive  Input  Devices and  are  classified  as:-

(a)Keyboard

(b)Locator  devices

(c)Interface  or  pick  devices.

   Keyboard

The  most  common  input  device  is  the  keyboard. The Modern  keyboard  generally  contains  104  keys  and  is called  the QWERTY  keyboard  because  of  the  sequence  of  keys  in  the  top  row,which are  similar  to  those  of  a  standard  typewriter.  A keyboard  is used for a wide range of tasks but is well known for its capability to enter data, which is copied from the original paper documents (such as name and address details on a form). Keyboards are also used for typing letters,memos,  reports  and  other  documents  using  word processing  software.

(b)    Locator  devices

Locator  devices  are  used  to  control  the  location or  position  of  the  cursor  on  the  screen  and they allow  us  to  provide the necessary  input.  Generally,  locator  devices  are  good  for gross movement  but  not  for  precision  work.  

Interface/Pick  Devices

Pick devices are used to select an object on the screen. The object may be  text  or  graphic.  Examples  of  pick  devices  are  light  pens  and  touchscreens.

Light  Pens

The  light  pen  is  a  pen-like  light-sensitive  device  that  feeds  a  narrow electrical  pulse  generated  by    a  pointing  device  directed  towards  the screen. It is connected by a wire to the computer terminal that detects the  signals  from  the  screen.  Light  pens  may  be  used  in  place  of  amouse  or  a  keyboard,  particularly  for  menu  based  applications  where an option may be selected by pointing on it. They are used for Computer Aided Designing  (CAD) and drawing purposes. Moreover, with the help of a light  pen,  engineers,  architects  or  fashion  designers  can  draw  and edit  the  designs  directly  on  the  screen,  though  for  editing  a  drawing keyboard  may  be  used  to  select  colours,  lines  with  varying  thickness,cropping  or  enlarging  the  drawings.  It  is  also  used  to  read  bar  codes from  products  that  are  available  in  big  departmental  stores.

Touch Screens

Touch  screens  are  monitors  on  which  the  user  makes  selections  by touching  the  screen,  rather  than  moving  a  cursor  to  the  location  with external  locator  devices.

Touch  screens  are  often  used  in  situations  where  users  are  likely to have a low level of competence in using computer keyboards. Touch screens  are  sometimes  used  in  restaurants,  building  societies  and

travel  information system.

Data Entry Devices:- We have observed that in  grocery stores, the clerks merely wave the product over a laser scanner/barcode reader, whichautomatically enters the product code and retrieves the corresponding price of  the  product  automatically.  The  earlier  practice  was  to  enter  the  code/product  name  by  using  a  keyboard  (a  time  consuming  process).  The  laser scanner/barcode reader comes under Source Data Entry Devices category,which increases the efficiency of a user. These devices help us in entering the  data  directly  from  the  source,  without any human intervention.

devices  used  in  this  category  are:-

(a)Video  digitiser

(b)Digital  camera

(c)Scanning  devices

(d)Voice  input

(e)Remote  control

(f)Magnetic  stripe  reader

(g)Sound  sensor– microphone

(h)MIDI  instrument.

Source Data Entry Devices

Video  Digitiser

A  video  digitiser  captures  television  pictures  from  devices  such  as  a TV set, video camera or video recorder and converts them into a digital format  that  a  computer  can  use  for display,  storage  or  general manipulation.  A  video  digitiser  is  an  ideal  tool  for  capturing  images from  real-life  scenes  to  incorporate  into  computer  work.  It  is  used  to convert  still  or  moving  images  into  a  digital  format  required  for computerised  presentation.  Taking  video  pictures  or  frames  from  video files  is  known  as  ‘frame  grabbing’.

A video digitiser may be required for video conferencing. (If a digital video camera is used there will be no need for a video digitiser.)  It can also  be  used  to  make  television  advertisements  and pop videos etc.

Advantages

• Video  digitisers  allow  us  to  capture  real-life  images  which  are  often more  appropriate  than  drawings.

• Captured  images  can  then  be  transferred  to  paper.

Disadvantages

• A  fast  computer  with  a  large  memory  capacity  is  required  to  cope with  the  large  amount  of  data  involved.

  Digital  Camera

A digital camera stores  images  (digital  pictures)  in  the memory  and  does  not  use celluloid films  as  in  the  case  of  ordinary cameras.  Each  digital  picture  is  made  up  of  thousands  of  tiny  dots,called pixels (picture  elements),  and  the  camera stores  data  about  the  colour  of  each  dot.  Thepicture  quality  is  determined  by  the  number  ofdots  representing  a  specific  picture. Theresolution  of  the  image is  expressed  in  Dots  PerInch  (DPI) defines.  Higher  the  DPI,  better  there solution. Most cameras allow the user to choosethe  resolution  needed  for  a  picture.  Once  thephotograph  is  stored  in  the camera  it  can  be transferred to a computer where it can be edited, printed  or  more  permanently  stored.  Somecameras store images on a floppy disk or memorycard  so  that  they  can  be  easily  transferred.  Other  cameras  areconnected  to  the  computer  with  a  lead  (cable)  and  special  software

is  used  to  transfer  the image.

Advantages

• There  is  no  developing  cost,  no  film  is  needed  and  we  can  insert

images  directly  into  a  document  on  the  computer.

• You  can  edit,  enlarge  or  enhance  the  images.

• An image can besaved with multiple shots and the best one can be saved.  That  is,  there  is  no  wastage  like  a  miss-shot  in  ordinary cameras.

Disadvantages

• Digital cameras are generally more expensive than ordinary cameras.

• When  the  memory  is  full  they  can  be  connected  to  a  computer  to

download  the  stored  images  (or  the  images  can  be  deleted  from

memory)  before  they  are  used  again.  This  is  not  as  convenient  as

simply  changing  a  film.

Scanning  Devices

• Scanner

A scanner is a device which can capture still images or  even  text,  to  be  stored  and  used  on  a  computer.

The  scanner  throws  a  light  beam  onto  the  paper and measures the amount of light reflected back by each  part  of  the  page.  Like  a  digital  camera,  the page  is  split  into  tiny  pixels  (dots)  and  a  number representing  the  colour  of  each  dot  is  sent  to  the computer. Scanner software usually allows the user to  choose  between  high  and  low  resolution.  Very High  quality  images  take  up  a  lot  of memory.

Most  scanners  need  to  place  the  paper  on  a glass  plate  inside  them  for  scanning  similar  to    a photocopier  machine.  These  are  called  flatbed scanners and  typically  use  a  charge–coupled  device  (CCD)  as  a  image  senser.  Thisusually come in A4 size or larger (such as A3), but there  are  also  some  small  hand-held  ones often used to read text such as bar codes.

Another  type  of  scanners  used  to  capture  the highest  resolution  from  an  image  are  called  drum scanners.  These  scanners  spin  the film around on a drum while a fixed laser or other beam of light looks at the art as it spins. The beam is then picked up by a very sensitive vacuum tubecalled a photomultiplier tube (PMT). This big single,fixed  tube  is  much  more  sensitive  to  light  than any  of  the  tiny  pixels  on  CCD  and  therefore  can see  a  broader  range  of  light  from  white  to  black.At  also  sees  it  without  the  noise  of  a  CCD.  Drum  scanners  are  good because  the  image  is  picked  up  by  a  much  more  sensitive  PMT.

Advantages

• Any  image  can  be  converted  from  paper  into  digital  format  and

later  enhanced  and  used  in  other  computer  documents.

Disadvantages

• Images  take  up  a  lot  of  memory  space,  but  it  is  possible  to  reduce

the  size  of  the  data  file  by  reducing  the  resolution  (number  of  dotsper inch) or by using different ways of storing the data i.e.,different file  formats.Whether  to  go  for  a  flatbed  or  a  drum  scanner  depends  upon  the objectives  of  our  scanning.  

• Optical Mark Readers (OMR)

Optical Mark Readers are able to detect marks on paper. A pre-printed document  is  prepared  for  users  to  select  certain  areas  to  put  a  line  ora  mark.  A  document  like  this  is  scanned  using  reflected  light  to  detect dark  shadows.Universities  and  educational  institutes  often  use  pre–printed enrolment  forms  where  students  have  to  enter  a  mark  with  a  medium or soft pencil. Multiple choice questions in entrance examination papers often  require  a  candidate  to  make  a  mark  to  indicate  the  answer.  Thestudent  will  pencil  a  line  through  the  option  of  their  choice.Questionnaires  and  surveys  may  also  use  this  technique.

Advantages

• Simply  selecting  and  marking  a  choice  in  the  right  location  on  an OMR  form  is  easier  than  typing and writing  in  data.

• Documents  can  be  checked and evaluated  very  quickly  by  scanning them  with  only  a  few  chances  of  error  (only  2–3%  with  modern OMR  machines).

Disadvantages

• Careful  handling  of  forms  is  needed.  Badly  damaged,  creased  or

folded  forms  may  be  rejected.

• They can only be used when the data to be input can be selected bymarking  with  lines.  Because  every  option  must  be  catered  for,  theforms are sometimes not very easy for the user to understand. This may  introduce  error.

• Optical  Character  Readers  (OCR)

Optical  Character  Readers  (OCR)  are  devices  that  can  detect  patterns

of  marks  which  are  in  character  format  (numbers,  letters,  punctuation and  some  special  characters  like ‘–,@’,  etc.).  Only  printed  characters can  be  recognised  because  it  is  not  easy  to  cater  for  different  styles  of handwriting.  The  characters  are  converted  by  a  scanner  from  picture format  into  coded  characters  that  the  computer  can  work  with.  This  is

normally  in  ASCII  format  (American  Standard  Code  for  Information Interchange).  OCR  software  can  be  purchased  separately  for  use  witha  standard  A4  scanner.  OCR  is  often  used  to  scan  text  for  use  in  aword  processor.

Advantages

• When a computerised document has not been saved and only printed text  is  available,  it  is  possible  to  use  OCR  to  scan  in  the  text  for later  editing  and  re-arrangement.

Disadvantages

• Some  characters  cannot  easily  be  interpreted  and  errors  occurduring  conversion.  This  is  especially  true  if  there  are  a  lot  of diagrams  and  characters  laid  out  in  a  way  the  software  cannotinterpret.

 Magnetic  Ink  Character  Recognition  (MICR)

Characters which have been printed using magnetised ink can be recognisedusing  a  Magnetic  Ink  Character  Reader  device.  This  type  of  data  collectionhas  limited  use  and  it  is  mainly  restricted  to  banking  systems  because  ofthe  expensive  equipment  involved.  Cheques  are  pre-printed  with  some code  and  account  number.  When  a  cheque  has  been  written  the  data input  clerk also has  to  mark  the  cheque  amount  in  magnetic  ink. MICR  is  used  for  Bank  cheque  processing.

Advantages

• Fast  processing  of  large  volumes  of  data.

• It  is  a  fairly  secure  method  of  data  collection  as  the  shape  of  the

characters  cannot  be  changed  without  expensive  equipment.

• This  method  of  input  is  very  reliable  as  the  number  of  errors

generated  during  the  reading  of  documents  is  negligible.

Disadvantages

• MICR  is  expensive  to  use  because  special  equipment  is  needed  to

create  the  characters  as  well  as  to  read them.

Bar–Code  Readers

Bar-  codes are  a  series  of  thick  and  thin  vertical  linesgrouped together. Bar-codereaders are the device used toinput  data  from such sets  of  Bar  codes.  Thereader  uses  a  laser  beam  to  read  the  series  ofthick and thin lines which represent the barcode number.  Almost  every  product  we  see  onsupermarket shelves has a barcode. The barcodeis  13  digits  long  and  there  are  four  maindivisions. The first part of the barcode (two digits)represents  the  country,  the  second  partrepresents  the  manufacturer’s  code  (five  digits),

the  third  part  represents  the  produce  code  (fivedigits) and there is a final digit, which representsthe  check  digit.  This  last  digit  is  a  calculated digit  to  ensure  that  the  barcode  is  read  properly.If there is an error, the reader usually beeps andthe  operator  must  key  in  all  the  digits  manually.

When  the  barcode  is  read,  it  locates  the  correctproduct  on  the inventory  file,  stored  on  thecomputer’s  disc.  The  price  is  read from  the  fileand  a  sale  is  registered,  producing  a  record  on the  customer’s  receipt.  The  number  filed  in theinventory  file  is  reduced  by  one.Bar  codes  are  used  on  library  tickets,  airportbaggage  labels,  books,  supermarket  products,clothes  and  on  many  other  retail  items.  Barcode  readers  are  used  inmost  situations  where  there  is  an  Electronic  Point  of  Sale  terminal (EPOS  terminal),  for  example:  department  stores,  supermarkets.

Advantages

• Fast  and  accurate  data  entry.

• It is possible to store all the details about the country of origin andmanufacturer as well as the product code itself. These are recorded in  a  standard  format  within  the  barcode.

Disadvantages

• If  the  barcode  is  damaged  the  barcode  reader  cannot  read  it.  It  is then time consuming to enter all the separate digits using a keypad.

Voice  input

We can now input data by simply talking into a microphone and usingspecial  software  to  recognise  the  voice.  Users  should  be  trained  inthe  software  regarding  correct  pronunciation  of  the  words  before  thespeech  can  be  interpreted  and  transferred  to  the  computer. 

Some computer systems can respond to voice commands and can carry outtasks  because  the  spoken  word  is  interpreted  by the software  and converted  to  instructions.  These  can  be  used  for  inputting  text  toword  processing  software,  controlling  devices  such  as  electronically controlled  doors  and  machines

Advantages

• Voice  input  is  extremely  useful  for  those  users  unable  to  usekeyboards  or  mouse.

Disadvantages

• The system must be able to recognise the voice of each user. ‘Teaching’the  software  can  be  tedious  and  time  consuming.

• Speech  recognition  software  is  still  not  very  accurate.

  Remote  Control

Remote  control  devices  are  used  for  transmitting  data  when  the  useris at some distance from the processor.Devices such as video recor derscan  accept  data  which  is  programmed  into  the  system  from  a  remotehandset.  Special  keys  for  certain  tasks  or  selections  are  usually  foundon  the  handset.  An  infrared  sensor  on  the  main  processing  unit  picksup  the  signals  when  keys  are  pressed.  It  is  used  to  enter  data  from  adistance.

Advantages

• The  device  provides  the  user  with  the  convenience  of  inputting  and

working,  away  from  the  processing  unit.

Disadvantages

• Small  remote  devices  can  easily  be  misplaced.

• The unit and remote need to be quite near to each other and should have  no  other  objects  between  them  which  may  interfere  with  the

signals  sent.

  Magnetic  Stripe  Reader

Magnetic  stripes  are  the  dark-looking  stripe  that  may  be  seen  onthe back of many plastic cards, for example, bankcards. The magneticstripe  holds  data  about  the  owner  of  the  card,  a  bankcard  will contain  details  such  as  the  bank  account  number  (the  card  owner’s individual  account  number)  and  sort  code  (the  code  that  identifiesthe branch of the bank where the account is held).The  device reads  the  data  on  themagnetic  stripe  and  money  can  be  taken  fromthe  correct  account  to  pay  the  bill. The  money  istaken  from  the  bank  account,  not from the  card.Data  on  a  magnetic  stripe  does  not  change  andthere  is  no  balance  recorded  on  the  card.  It  maybe noted that the card does not contain details ofthe credit limit. Magnetic stripe readers are oftenseen at supermarkets and in many different typesof shops, in fact anywhere wherethere is a ‘pointof  sale’  (somewhere  we  pay  for  our  purchases). When the data is read electronically, the point of sale is called EPOS(Electronic  Point  of  Sale).

Advantages

• The  card  can  be  read  many  times  without  damaging  the  stripe.

• The  data  is  not  visible  to  people  because  a  machine  is  needed  toread  the  data  (although  with  debit  cards  the  bank  details  areactually  displayed  on  the  card  as  well).

• Putting  magnetic  stripes  onto  cards  is  not  expensive  so  the  cardsare  quite  cheap  to  produce.

• The data from the stripe is read very quickly and more conveniently.

Disadvantages

• Magnetic  stripes  may  get  damaged  or  the  magnetic  stripe  reader could  break  down.

• The  biggest  disadvantage  of  magnetic  stripes  is  that  ordinary

equipment  can  read  but  not  change  the  data.  That  is  why  SmartCards  are  gaining  more  popularity.  These  cards  contain  a  small  chip(or  tiny  processor  with  some  memory)  instead  of  a  magnetic  stripe. The data on the chip may then be changed as the smart card is used.

Sound  SensorMicrophone

A  sound  sensor,  which  is  a  microphone, is  a  device  thatdetects sound and inputs it to the computer, and thenthe  sound  which  is  analogue  in  nature  is  converted into  digital  format.The  person  using  the  computer  speaks  into  themicrophone.  Speech  recognition  software  on  thecomputer  converts  what  the  person  has  said  intotext. The text is displayed on the screen and can besaved  as  a  word-processed  file.  Speech  recognitionis  getting  more  reliable  though  it  is  necessary  tospend  some  time  ‘teaching’  the  system  to  recognisethe  user  speech.  Remember,  it  still  does  not  alwaysmake  accurate  conversions  to  text. Some  users  record  special  sounds,  both  voiceand  music,  from  any  source.  These  sounds  may  beused  in  computerised  presentations,  for  example,  multimedia  teaching software.

Advantages

• People  with  a  range  of  disabilities  can  be  benefited  from  the  use  of microphones and speech recognition, for example, those who cannotuse  a  keyboard.  They  can  create  word-processed  documents  byspeaking  instead  of  typing.  Moreover,  many  devices  in  the  home can  now  be  controlled  by voice.

• Recording our own sounds means that we can add spoken messagesor  music  to  our  own  presentations  or  even  e-mails.

Disadvantages

• There  should  be  no  background  noise  while  recording,  otherwise sound  may  become  distorted.  Cutting  down  the  background  noise is  sometimes  difficult  and  the  sound  recorded  using  a  microphone is often not very good.

•  Sound  sampling  (converting  the  analogue  sound  to  digital  format using  software)  often  produces  very  large  data  files.

MIDI  (Musical  Instrument  Digital  Interface) 

 InstrumentIt  is  a  serial  interface standard  that  allows connections  of music  synthesisers, musical instruments  and computers.There are  a variety  of  musical  instruments  such  as keyboards,  guitars  and  drums,  which  send and  receive  electronic  messages.  If  a  musical keyboard is connected to a computer using a MIDI  instrument,  the  musical information such as pitch is converted to digital data which can then be stored on the computer. The  music  industry  uses  MIDI  to  input music directly into a computer so that it can be  edited  and  developed,  often  by  mixing  it  with  other  sounds  which are  input  from  a  microphone.  Some  programs  allow  its  user  to  enter  atune  from  a  musical  instrument,  then  convert  this  into  written  music,which  can  even  be  printed  out.

Advantages

• Once  the  tune  has  been  played  on  the  musical  instrument,  all  the

details are held on the computer. These details may then be changed.

It  is  possible  to  speed  up  the  tune,  slow  it  down  or  even  make  it sound  like  a  completely  different  instrument.

• The  data  stored  is  very  compact  and  takes  up  about  1/20th  of  the

space taken up by even the lowest quality recorded sound samples.

Disadvantages

• A  musician  is  required  to  play  the  instrument  to  acquire  the  input,

so  some  musical  knowledge  is  required.

• To  take  advantage  of  the  digitally  recorded  sound,  knowledge  of

software  and  music  is  required  to  edit  recorded  tunes.

MEMORY OR STORAGE DEVICES

Memory  is  required  in  a  computer  to  store  programs  and  the data processesd by programes.

Computer memory is made up of a large number of cells. Each cell is capable of storing one bit of information in the form of binary numbers.

Memory System

Memory in a computer system is required for the storage and subsequent retrieval  of  instruction  and  data.  A  computer  system  uses  a  variety  of devices  for  storing  instructions  and  data  required  for  its  operations.Normally,  the  information  to  be  stored  on  a  computer  is  classified  intwo  basic  categories– data  and  instructions.

Although  a  memory  system  is  a  very  simple  system,  it  exhibits  awide  range  of  technology.  But  unfortunately,  faster  memory  is  more costly.  On  the  other  hand,  memories  with  smaller  cost  have  very  high access  time.  This  is  the  time  taken  by  the  CPU  to  access  a  location  in

memory.  This  results  in  slower  operation  of  the  CPU.  Thus,  the  costversus  access  time  has  led  to  a  hierarchy  of  memory  where  we supplement  fast  memories  with  larger,  cheaper  and  slower  memories.Therefore,  memory  systems  may  have  different  types,  costs,organisations,  technologies  and  performances.  

Types of Memory

A  memory  system  can  be  considered  to  consist  of  three  types  of memories.  These  are  as follows:-

1.Internal  processor  memories

2.Primary  memory  or  main  memory

3.Secondary  or  auxiliary  memory

Any storage unit of a computer may havethefollowing characteristics:

• Storage  capacity is  the  amount  of  information/data  a  storage  unitcan hold. Accessing the data to/from these memories may be fast or slow.

• Thespeedand availability of inexpensive memory has had enormousimpact  on  computer  technology.  The  high  speed  memory  devices  aremore expensive and occupy less space in comparison to the slow speed memory  devices.

Internal  Processor  Memories

These  consist  of  the  small  set  of  high-speed  registers  and  high  speed

buffer  memory  (cache)  which  are  internal  to  a  processor  and  are  usedas  temporary  locations  where  actual  processing  is  done.

Register is  a  small  amount  of  storage  available  on  the  CPU  whoseontents can be accessed more quickly than storage available elsewhere.Processor registers are at the top of the memory hierarchy and provide the  fastest  way  for  a  CPU  to  access data.

Cache  Memory

Cache  memory  is  a  small  high  speed  buffer  memory  used  to  hold instructions  temporarily  during  processing.The  CPU  of  a  computer  system  commonly  uses  cache  memory  where it holds or buffers the contents of the main memory becsusr of the CPU  runs  much  faster  than  the  main  memory.  Thus  toreduce  the  waiting  time  of  the  CPU  the  cache  is  used.  

Cache  memory reduces  traditional  system  bottlenecks  because  system  RAM  is  much slower than CPU. This prevents the processor from having to wait for a program  and  data  from  slower  main  memory. A cache  typically  operates  by  retaining  copies  of  blocks  of  storage,each  containing  recently  used  information.  This  memory  (or  caches)  is usually  transparent  or  invisible  to  the  processor.

Primary memory

It is a large memory which is fast but not as fast as an internal processor register.  The  processor  directly  accesses  this  memory.  It  is  mainly based  on  integrated  circuit.

The primary  memory or  the main  memory is  part  of  the  maincomputer system. The processor or the CPU directly stores and retrievesinformation  from  it.  This  memory  is  accessed  by the CPU,  in a  randomfashion. That means any location of this memory can be accessed by theCPU  to  either  read  information  from  it,  or  store  information  in  it.  Theprimary  memory  itself  is  implemented  by  two  types  of  memorytechnologies. The first is calledRandomAccessMemory(RAM)and the other  is  read  only  memory  (ROM).  A  more  appropriate  name for Ram is RWM  (read  write  memory),  the  CPU  can  write  and  read  informationfrom  any  primary  memory  location  implemented  using  RAM.  The  other part  of  primary  memory  is  implemented  using  ROM  which  stands  for Read  Only  Memory.

There  are  two  types  of  built-in  memory,  permanent  and  temporary,

known  as  ROM  and  RAM,  respectively,  details  of  each  given  below:-

ROM

Read  Only  Memory  (ROM)As  we  know,  in  the  computer  terminology, read means  transferring data instruction from an input source to the computer's main memory (or CPU)  and write is transferring  data/instruction  from the computer's main  memory  to  an  output  device.  Therefore,  read  only  means  data/instruction can be retrieved from the ROM chip but cannot be modified.

Types of ROM

Basically,  there  are  two  types  of  ROM,  namely,  manufacturer

programmed and  user-programmed.

Manufacturer–Programmed  Read Only Memory

Manufacturer-programmed  ROM  is  one  in  which  data  is  stored  in  it permanently by the manufacturer of the ROM.

For example, a computer manufacturer  may  store  the  system  boot  program  permanently  in  the ROM  chip  used  on the motherboard.

User–Programmed  Read  Only  Memory

User-programmed  ROM  is  one  in  which  the  user  can  load  and  store“read-only”  programs  and  data.  Such  a  ROM  is  commonly  known  as PROM(programmable read-only memory), because a user can program it. 

PROM(programmable read-only memory) is  a  memory  chip  on which we can store a program. But once the PROM has been used, we cannot  wipe  it  clean  and  use  it  to  store  something  else.  Like  ROMs,PROMs  are  non-volatile.

Other  kinds  of  user-programmed  ROM  are  EPROM  and  EEPROM. Both  of  these  are  special  types  of  PROM.   

EPROM(erasable programmable  read-only  memory)can  be  erased  by  exposing  it  to ultraviolet  light  while EEPROM(electrically  erasable  programmable read-only memory)can be erased by exposing it to an electric charging.

Random Access Memory (RAM)

RAM  chips  are  meant  for  primary  storage.  They  hold  temporarily

(a) software/program instructions and (b) data before and after processing.

"Rabdom Access”  means  that  any  location  can  be  referenced  in  thesame time and in the same manner, as it is independent of the addressor  location  in  the  memory.  It  is  a  volatile  memory.  It  holds  data  and

instructions,  during  their  execution.  

The  additional  RAM  chip  can  be

plugged  into  the  special  socket  on  the  motherboard  known  as  Single

In-Line  Memory  Module  (SIMM).  Random  Access  Memory  capacity

ranges from 16 MB to 4 GB on personal computers.

Types of RAM

RAM  chips  are  of  two  types,  namely, static  RAM  (SRAM)  and dynamic RAM  (DRAM).

Static  RAM  (SRAM)

The SRAM can store data as long as power is applied, without the need for periodically rewriting the data into memory. Contents (memory cell)of  this  RAM  will  stay  in  a  given  state  (store  a  bit)  indefinitely,  provided

that  power  to  the  memory  circuit  is  not  interrupted. The  main applications of SRAM are in areas where only small amounts of memory are  needed  or  where  high  speed  is  required.

Advantage

SRAM  can  provide  very  high  speeds.

Disadvantage

SRAM  is  costly  and  has  low  power  packing  density.

Dynamic RAM (DRAM)

This memory stores data as charges on capacitors. With Dynamic RAM,

the stored data will gradually disappear because of capacitor discharge,so  that  it  is  necessary  to  periodically  refresh  the  data  (i.e.  recharge the  capacitors).  In  the  process  of  refreshing,  the  information  is  read

from the memory cell and written back in the same position. Typically, each  memory  cell  of  a  DRAM  must  be  refreshed  at  least  every  2  to  10

millisecond  or  its  data  will  be  lost.

Advantage

It  has  high  capacity  and  power  consumption  is  low.

Disadvantage

The  need  for  refreshing  of  dynamic  RAM  because  some  external refreshing  circuits  are required.

Secondary or Auxiliary  Memory

Auxiliary  memory  is  much  larger  in  size  than  main  memory  but  is slower  than  the  latter.  It  normally  stores  system  programs  and  data files.  These  cannot  be  accessed  directly  by  the  processor.

Secondary  or  auxiliary  memory,  also  known  as    secondary  storage,is  the  memory  that  supplements  the  main  storage.  This  is  a  long-term, non-volatile  memory.  The  term  non-volatile  means  it  stores  and  retains the  programs  and  data  even  after  the  computer  is  switched  off.  Unlike RAM  which  looses  the  contents  when  the  computer  is  turned  off  and ROM  to  which  it  is  not  possible  to  add  anything  new,  auxiliary  storage device  allows  a  computer  to  record  information  semi-permanently.  This Is to ensure that this information can be read later by the same computer or  by  another  computer.  Auxiliary  storage  devices  are  also  useful  in transferring  data  or  programs  from  one  computer  to  another.  They  also function  as  backup  devices  which  allows  backup  of  the  valuable information  that  we  are  working  on.  So,  even  if  by  some  accident  our computer  crashes  and  the  data  in  it  is in unrecoverable  mode,  we  can restore it from your backups. The most common types of auxiliary storage devices are floppy disks, hard disks, magnetic tapes and Magnetic disk.

CENTRAL PROCESSING UNIT

       

The central processing unit is one of the two most important components

of  the  microcomputer.    It  is  the  electronic  brain  of  the  computer.  In addition  to  processing  data,  it  controls  the  functions  of  all  the  other components.

The Central Processing Unit (CPU) or the “Central Processor” carries out  a  variety  of  essential  data  manipulation(includingarithmetic/logical  calculations,  comparisons,  sorting,  etc.) and  controlling  tasks in the computer. 

CPU consists of Arithmetic Logic Unit (ALU) and cntre unit (CU).

Every microprocessor  contains  a  system  clock.  The  speed  at  which

the processor executes instructions is known as Clock Speedand it is measured  in  Megahertz  (MHz).

Megahertz  (MHz):- a  measure  of  frequency  equivalent  to  1  million cycles  per  second.

Gigahertz  (GHz):- a  billion  cycles  per  second.

Arithmetic Logic Unit

The  Arithmetic  Logic  Unit  carries  out  as  the  name  suggests  Arithmetic And Logical operations on the data made available to it. Basic Arithmetic Functions  which  an  ALU  can  carry  out  are  addition  and  subtraction.More  powerful CPUs can  support  additional  mathematical  operations like  multiplication  and  division.  The  logical  operation  which  it  can carry out are greater than, equal to, less than and comparison between

two  numbers.  Besides  these  operations  some  processors  also  support operations  which  check  if  particular  bits are on or off.

CONTROL UNIT

The  Control  Unit  can  be  thought  of  as  the  brain  of  the  CPU  itself.  It controls  the  computer  based  on  the  instructions  it  decodes,  how  other

parts of the CPU and in turn, the rest of the computer systems should work  in  order  that  the  instruction  gets  executed  in  a  correct  manner.

Register

The  register  is  a  special,  high-speed  storage  area  within  the  CPU.  All

data  must  be  represented  in  a  register  before  it  can  be  processed.  For Example,  if  two  numbers  are  to  be  multiplied,  both  numbers  must  be in  registers,  and  the  result  is  also  placed  in  a  register.  (The  register can  contain  the  address  of  a  memory  location  where  data  is  stored rather  than  the  actual  data  itself.).

OUTPUT DEVICE

The output  devices  of  the  computer  are  used  to  display  results  in electronic  or  paper  medium.Common  output  devices  which  produce  output  that  is  easily understood  are Printers  and  Monitors.

The  results  generated  by  the  output  devices  may  be  of  two  types:-

Hardcopy Output:- Such outputs are non-electronic version/permanent,and

thus may be used at later date as and when they are required. Theyare  usually  on  paper  and  are  generally  used  to  produce  reports.  Thedevices  which  are  used  to  produce  hardcopy  output  are  printers,  graph

plotters,  computer  output  microfilm,  etc.

Softcopy Output:- Such outputs are electronic, thus they are availableeither on screen or may be stored digitally on some storage device. Thesoftcopy may be directly seen on screen or may be stored on hard disk/CD/  DVD  for  further use.

Printers

A printer is an output device that prints characters, images and symbols on paper. On the basis of the printing technique used, printers may be classified  as impact or non-impact  printers.

Impact printers

Impact printers are like typewriters, as they use some sort of striking/hammering  action  to  press  carbon  or  fabric  ribbon  against  paper  to create  a  character  or  a  pattern.  These  devices  are  noisy  and  are  not capable of producing high resolution graphics. The most common impact printers  are character printers  (e.g.  daisy  wheel,  dot  matrix)  and line printers (e.g.  chain  printers,  drum  printers).  Among  impact printers,  line printers print  one  line  at  a  time,  so these  printers  are  extremely fast.  Impact  printers  are  ideal  to  be  used  for  carbon  copies.

Dot-matrix  Printers

The  print  head  of  Dot-matrix  printers  uses  small  pins,which  strike  on  the  paper  to  create  a  character  or  image.  They  are more  economical  than  most  of  other  types of printers,  with  lowest  running  cost.  These  printers are not used much now-a-days. However, at places where  invoices  and  delivery  notes  are  produced with a copy and the quality is not important, these are  still  used.

Advantages

• The main advantage of dot-matrix printers now is  the  ability  to  produce  carbon  copies.  They Provide  a  cheap,  reliable  method  of  getting multiple  copies  of  a  printout.

• The  other  advantage  is  the  low  cost  of  printouts.  It  has  low maintenance  and  running  costs.

Disadvantages

• Dot-matrix  printers  are  noisy,  slow  and  produce  a  lower  quality

output.

Non-impact  printers

 overcome  the  limitations  of  impact  printers.  Theyform  characters  or  images  without  making  print  heads  strike  the  paper. They use thermal, electrostatic, chemical or inkjet technology to produce printed  output.  They  are  fast  and  quiet  in  operation. The  most  common non-impact  printers  are inkjet  printers and laser  printers.  These printers  can  come  in  two  categories,  one  produces  output  with  only  one colour (i.e. black colour) and the other one produces output in multicolour.

Day–by–day,  with  advancement  in  the  field  of  printing  technology,the  quality  and  speed  of  these  printers  are  going  up  and  prices  arecoming  down.  Colour  printers  are  increasingly  being  used  in  homes and  offices alike.

Inkjet Printers

Inkjet printers use liquid ink  technology.  These  printers are available in comparatively lower prices and are capable of producing reasonably  good  quality  prints.  The  running  cost  of  these  printers  is very  high  and  so  are  not  preferred  by  those  seeking  large  volumes  of prints. These printers are relatively noiseless during printing operation.

Advantages

• Inkjet  printers  are  relatively  inexpensive  to  buy,  especially  if  colour is needed.

• Inkjet  printers  are  also  lighter  in  weight than  other  printers  and  some  are  small enough  to  be  carried  around  in  a portable carry  case.

Disadvantages

• Inkjet  printers  are  slower  than  laser  printers.

• If  left  unused  for  long  periods  of  time  the cartridges  can  easily  dry  out.

•Colour  cartridges  are  expensive  in  comparison.

Laser  Printers  (Non–Impact  Printer)

Laser  printers  produce  high  quality  paper  prints at  a  high  speed  (with  an  average  speed  as  6  to  12 pages  per  minute).  They  are  almost  noiseless  and use  dry  magnetic  ink  technology.

Advantages

• Laser printers are noiseless, high speed and high quality  printers.

• Laser  printers  are  comparatively  economic  for a large  number  of  printouts.

Disadvantage

• Initial  costs  of  laser  printers  are  comparatively high.

• Size  of  laser  printers  is  comparatively  bigger.

• Repair  costs  and  cartridges  of  these  printers  are generally  expensive.

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