handout 2 computer basics

8/8/2019 Handout 2 Computer Basics

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IT in Business Teacher: GUL MUNIR UJJAN

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Chapter One Contd…

Computer Basics

• Bits and Bytes

• Coding techniques: ASCII , ANSI, Unicode, EBCDIC• Basic functions of Computers: Input, Processing, Storage, Data movement,

output

• CPU and CPU Components

Ø CPU and ALU

Ø CPU registers

Ø Decoder

• I/ O Ports

• Storage: Primary Storage

o ROM & its Types

o Ram & its Types

o Cache Memory

• Secondary Storage

o Hard disks§ Formatting

§ De-fragmentation

o Optical disks

• Source Data Entry Devices

o OCRs

o OMRs

o MICRs

o Barcode Readers

o Scanners / Photocopier / Fax Machines




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Secondary storage media

Ø Secondary storage represents hardware devices that personally hold data and information as well as programs.

Ø However most computer operating systems also use secondary storage devices as virtual memory to artificially

increase the apparent amount of main memory in the computer. Secondary storage is also known as "mass

storage".

Ø Secondary or mass storage is typically of much greater capacity than primary storage (main memory).

Ø But it is also very much slower.

Ø In modern computers, hard disks, floppies, USB drives, optical disks etc are usually used for mass storage.

Magnetic disks

Hard disk

Ø Thin but rigid metal platters covered with substance that allows data to be held in the form of magnetized spots.

Ø There can be several platters used within single hard disk containing at least single R/W head per surface.

Ø They are quite sensitive devices.

Ø It is faster than floppy. Unlike CDs and floppies, hard disk platters rotate continuously with approximate speed

of 7200 rpm, independent of access of data.

Formatting

Ø The process of preparing a disk so that it can store data files and program files.

Ø During formatting OS creates concentric circles called tracks. Each track is further divided into wedge-

shaped sections called sectors. A single sector can store data up to 512 bits or it’s multiple.




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Disk de -fragmentation

Ø The data stored on hard disk is normally scattered i.e. it is stored in several fragments and uses

nonadjacent areas of hard disk.Ø The scattering of portions of files about the disk in nonadjacent areas, thus greatly slows down access to

the files.

Ø Disk defragmenter utility program finds all the scattered files on a hard disk and reorganizes them as

contiguous files.

Ø De-fragmented disks provide quicker access; R/W arm needs to move less to access all sectors of a file.

Ø For better performance of computer the user should run de-fragmentation utility periodically.




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Optical disks

There are two basic types of optical disks: CDs (Compact Disks) and DVDs (Digital Video Disks or VersatileDisks)

Compact disks (CDs):

CD ROM

• Data is stored at the time of manufacturing.

• User cannot insert the data.

CD-R

• Data is written by the user.

• Not necessary to be written at the time of manufacturing.

• Once recorded can be read for many times but can’t be written again.

• CD-Rs are recorded with the speed of 8X for first time and then with 4X using CD writer drives. Where

X is equal to 150.

CD-R/W

• Can be written several times.

• Once written can be read several times.

• In CD-R/W drive, you can access CD-ROMs as well as CD-Rs.

DVDs (Digital Versatile/Video Disks)

• Extremely high capacity, able to store 4.7 to 17 GBS.

• More compression of data as compared to CDs.

• DVD Rom drives specially for DVDs but also support CDs.

• DVDs exist in all forms as in CDs with the same recording and reading characteristics i.e. DVD-ROMDVD-R, and DVD -R/W.

Optical disk drives (Working Principle)

The physical surface of optical disks is divided into pits (indentations) and lands (flat surface) where,Ø Pits represent 0.

Ø Lands represent 1.

Ø Sensors or lenses are used to read/write data instead of R/W head.

Ø Laser beams are used to identify pits and lands on CD surface.

Ø High power laser diode is used for writing of the data.

Ø Low power diode is used for reading the data.

Ø If the laser beam after passing through prism, is reflected by striking any spot on CD surface, the sensor

assume 1 at that spot, otherwise 0 in case it scatters




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Source Data Entry Devices:

Source Data Entry devices create machine-readable data on magnetic media or paper or feed it directly into

the computer. There are several types of source data entry devices. Some most common examples are

described below.

Ø Scanners / Photocopier / Fax Machines

Ø OCRsØ OMRs

Ø MICRsØ Barcode Readers

Scanner / Photocopier / Fax Machines

A scanner is a source data input device that uses light-sensing equipment to translate images of text, drawings, photos,and the like into digital form. Why it's important: Scanners simplify the input of complex data. The images can be

processed by a computer, displayed on a monitor, stored on a storage device, or communicated to another computer.

Scanners are similar to photocopier machines except they create electronic files of scanned items instead of pape

copies. The system scans each image – color or black and white – with light and breaks the image into rows and

columns of light and dark dots or color dots, which are then converted to digital code, called a bitmap. In photocopier,

the image or text is first scanned and then it is transferred to hard copy output.




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A fax machine or facsimile transmission machine scans an image and sends it as electronic signals over

telephone lines to a receiving fax machine, which prints out the image on paper. It acts at one end as scanner

and at the other end as printer like photocopier.

OCRs

Optical Character Recognition (OCR) software converts scanned text from images (pictures of the text) to an editable

text format (usually ASCII) that can be imported into a word processing application and manipulated. OCR Software

can deal with nearly all printed characters, but script fonts and handwriting still present problems. In addition, OCR

accuracy varies with the quality of the scanner

OMRs

Optical Mark Recognition (OMR) uses a special scanner that read “bubble” marks and converts them into

computer-usable form. The best known example in the OMR technology used to read students’ answers to the

College Board Scholastic Aptitude Test (SAT) and the Graduate Record Examination (GRE). In these casesthe scanner reads pencil marks that fill in circles, or bubbles, on specially designed documents.

MICRs

Magnetic Ink Character Recognition (MICRs) is a character recognition system that uses magnetizable ink

and special characters. When an MICR document needs to be read, it passes through a special scanner that

magnetizes the special ink and then translates the magnetic information into characters. MICR technology is

used by banks. Numbers and characters found on the bottom of checks (usually containing the check number

sort number, and account number) are printed with a laser printer that accepts MICR toner. MICR provides a

secure, high-speed method of scanning and processing information.

Barcode Readers

Barcodes are the vertical zebra – stripped marks you see on most manufactured retail products. Everything

from candy to cosmetics to comic books – Throughout the world supermarkets, food manufacturers, and

others have agreed to use a bar-code system called the Universal Product Code (UPC), established by the

Uniform Code Council (UCC).

Barcode Readers are photoelectric (optical) scanners that translate the symbol in the bar code into digital

code. There are three types of bar codes used now a days. One dimensional (1D), two dimensional (2D) and

three dimensional (3D) barcodes. They differ from each other with respect to the product physical structure

and the information that is written in barcode.

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