Grade:XI (Computer System)

1.    What is computer system or computer architecture? Explain the major units of computer system.

Ans: Computer architecture is defined as the science of selecting and interconnecting hardware components to create computers that meet functional performance and cost goals.

                     

                                                                                                                                                                  

Main components of computer system are explained below:

1.    Input Device

        Those devices which are used to input data and instructions to the computer generating electrical signal and convert into computer format for the further processing is called input device. E.g. Mouse, scanner, joystick, etc.

2.    Processor (CPU)

        Processor is the main component in computer, that is the heart of the computer system with circuitry to control the interpretation and execution of instructions. The internal components of microprocessor are as follows:

a.    CU (Control Unit)

Control unit controls the sequence of actions by the program and Input/ Output operation. It is nerve center of CPU. It controls the flow of data within the devices and supervises on the data flow.

b.   Arithmetic and logic unit (ALU)

It performs all type of arithmetic calculations such as addition, subtraction, multiplication and division and it also performs the logical and comparative analysis like AND, OR, NOT operator.

c.    Register arrays

It  is a temporary storage built inside a microprocessor to store a data before and after storing data in primary memory. The speed of the microprocessor is evaluated by number of registers in the microprocessor itself.

3.    Primary memory

      The internal memory unit which stores all currently being used data and instructions temporarily. It stores the data that before processing or displaying and it also provide space to the CPU for data processing. It is directly accessed by CPU.  

It has two types which are RAM and ROM.

RAM: It stands for Random Access Memory that stores currently being used data and instruction and provide space to the CPU. It is volatile memory as its contents can be edited and deleted. Its data are erased when the electricity is cut off so called electrically dependent memory.

ROM: It is read only memory. It is permanent built in memory stores firmware and check all the status of computer while booting the computer. It is non volatile type and electrically independent as its contents can not be deleted and altered even doesn’t erased when the electricity is cut off.

4.    Secondary Storage Device

        Secondary memory is where programs and data are kept on a long-term basis. Common secondary storage devices are the hard disk and optical disks. The hard disk has enormous storage capacity compared to main memory. The hard disk is usually contained inside the case of a computer. Some examples are: Optical disk, magnetic disk, flash memory, etc.

5.    Output device

Output devices are those devices which display the required result in simple words to the users. The output device provides the output of data or information. The purpose of the output devices is to translate data and information from electrical impulses to a human-readable format. There are two principal kinds of output. They are described below:

• Soft copy output

It refers to data that is shown on a display screen or sound produced by a speaker. It is present in a digital form on a computer. This kind of output is untouchable. It is temporary in nature. For example, content displayed on a screen.

• Hardcopy output

It refers to printed output printed on the paper or some material that can be touched and carried for being shown to others. It is permanent in nature and can keep in paper files or can be looked later when a person is not using the computer. For example, outputs produced on paper by printer or plotter in the form of text or graphics, etc.

2. What are input device? Explain.
Those devices which are used to input data and instructions generating electrical signals and converted it into computer understandable form for processing is called input device.
Keyboard
Keyboard is the most basic input device. It is used for text input. It contains multiple keys. User can provide input by pressing the key. The different types of key found in keyboard are:
a) Alphanumeric keys
b) Function keys
c) Special function keys
d) Cursor movement keys
e) Punctuation keys
f) Numeric pad
g) Multimedia keys
a. Mouse
Mouse is a most common pointing and selecting device. It is used in graphical user interface. Mouse contains buttons for providing inputs. User can provide inputs by moving the mouse and pressing the button. On the basis of working mechanism and its architecture, mouse can be classified as
a) Mechanical mouse
b) Optical mouse
Mechanical mouse contains a rubber ball and a pair of rotating wheels. When the mouse is moved on the table, the ball rotated which results in rotation of the wheels and generates electronic signal.
Optical mouse operates using reflection of light. It is easier to use but usually less reliable than mechanical mouse.
b. Track ball
Trackball is the modification of mechanical mouse. It contains rubber ball on its top. User can move the cursor by rotating the ball with finger. It also contains two buttons on the either sides similar to mouse. It was used in older laptops.
c. Track pad/Touch pad
Track pad is the modification of optical mouse, and touch pad is further modification making it touch sensitive. It contains a window with two buttons on the either sides. User can also provide left click option by tapping the window with the finger. It is mainly used in portable devices like laptops, notebook, palmtop, etc.
d. Joystick
Joystick is a hand held pointing device which is mainly used for playing games. It is used for controlling objects, their movement, direction and speed of movement. Modern joysticks handle can move in any direction. When the handle is moved, the electronic circuit in the base detects the movement and sends corresponding binary signals to CPU.
e. Light pen
Light pen is used for creating drawings, designs by directly touching the screen. It is mainly used by designers, architects, engineers, etc. it is used in monitor not having touch screen facility. It is a pen shaped structure containing photo sensitive tip which can capture light emitted from the monitor and mark the position on the monitor.
f. Touch screen
Touch screen is none of the common input device at present mainly for portable computers. User can provide inputs by directly touching the screen with the metallic pen (stylus), finger or any pointed object. Touch screen is developed by using either of the following technologies:
a) Pressure sensitive
b) Capacitive
c) Infrared
g. Scanner
Scanner digitizes hard copy or printed images which can be used in digital computers. Scanner copies the image and draws a new digital image in its memory similar to hard copy image.
h. OCR (Optical Character Reader)
OCR digitizes handwritten or printed text.
Printed text will have fewer errors than hand written. It directly converts hand written text into digital text which can be edited. OCR contains predefined format of all the characters. During digitizing process, it creates an image of the character and compares it with stored format to determine the character.
i. MICR
It stands for Magnetic Ink Character Reader. MICR is an OCR that can digitize text written or printed by using magnetic ink like iron oxide or barium ferrite. It is used in security systems and for processing cheque in bank.
j. OMR
It stands for Optical Mark Reader. It is used for answer sheet correction in multiple choice questions. With the use of OMR answer sheet correction will be faster and error free.
k. BCR
It stands for Bar Code Reader. Bar codes are the magnetic lines used for storing the information about the product like manufacturing date, expiry date, company name, etc. BCR is used to read the information stored in bar codes. Bar codes are also used in security system.
l. Microphone
It is an input device for sound. It captures sound wave, converts it into digital format and provides it to the CPU. Common mobile computing devices like PDA, smart phone contains microphone.
m. Digital camera, Web camera
Digital camera captures real time images and video and stores it in a digital format. The image captured by digital camera can be directly used in a digital camera.
Web camera is a digital camera used in internet. It usually captures low quality images so that it could be transmitted at a faster speed.
n. Card reader
It is used to read the information stored in cards like ATM card, Credit card, Smart card, etc.
o. Digitizing tablet
It is used to digitize large map or hardcopy images. It is also used to track the movements of living beings and capture them in digital format.

3. What is computer Memory? Explain its types.
Computer Memory– Memory is storage part in computer. It is store the data, information, programs during processing in computer. It stores data either temporarily or permanent basis. Memory used to play important role in saving and retrieving data.

Types of Memory– Mainly computer have two types memory
1. Primary Memory / Volatile Memory.
2. Secondary Memory / Non Volatile Memory.
1. Primary Memory / Volatile Memory– Primary memory is internal memory of the computer. It is also known as main memory and Temporary memory .Primary Memory holds the data and instruction on which computer is currently working. Primary Memory is nature volatile. It means when power is switched off it lost all data.
Types of Primary Memory– Primary memory is generally of two types.
1. RAM
2. ROM
1. RAM (Random Access Memory) – It stands for Random Access Memory.RAM is known as read /writes memory. It generally refereed as main memory of the computer system. It is a temporary memory. The information stored in this memory is lost as the power supply to the computer is switched off. That’s why RAM is also called “Volatile Memory”
Types of RAM– RAM is also of two types:
a) Static RAM- Static RAM also known as SRAM ,retain stored information as long as the power supply is ON. SRAM are of higher coast and consume more power .They have higher speed than Dynamic RAM
b)Dynamic RAM– Dynamic RAM also known as DRAM, its stored information in a very short time (a few milliseconds) even though the power supply is ON. The Dynamic RAM are cheaper and moderate speed and also they consume less power.
2. ROM (Read Only Memory) – It stands for Read Only Memory.ROM is a Permanent Type memory. Its content are not lost when power supply is switched off. Content of ROM is decided by the computer manufacturer and permanently stored at the time of manufacturing. ROM cannot be overwritten by the computer. It is also called “Non-Volatile Memory”.
Type of ROM: ROM memory is three types names are following-
a. PROM(Programmable Read Only Memory)-PROM chip is programmable ROM.it is PROM chips to write data once and read many.once chip has been programmed ,the recorded information cannot be changed. PROM is also nonvolatile memory.
b. EPROM (Erasable Programmable Read Only Memory)- EPROM chip can be programmed time and again by erasing the information stored earlier in it. Information stored in EPROM exposing the chip for some time ultraviolet light .
c. EEPROM (Electrically Erasable Programmable Read Only Memory)-The EEPROM is programmed and erased by special electrical waves in millisecond. A single byte of a data or the entire contents of device can be erased.
2. Secondary Memory / Non Volatile Memory– Secondary Memory is external memory of the computer. It is also known as Auxiliary memory and permanent memory. It is used to store the different programs and the information permanently. Secondary Memory is nature non volatile. It means data is stored permanently even if power is switched off.
The secondary storage devices are:
1. Floppy Disks
2. Magnetic (Hard) Disk
3. Magnetic Tapes
4. Pen Drive
5. Winchester Disk
6. Optical Disk(CD,DVD)
1. Floppy disk
A floppy disk is a magnetic storage medium forcomputer systems. The floppy disk is composed of a thin, flexible magnetic disk sealed in a square plastic carrier. In order to read and write data from afloppy disk, a computer system must have a floppy disk drive (FDD).
2. Magnetic tapes
A magnetic tape drive is a storage device that makes use of magnetic tape as a medium for storage.
It uses a long strip of narrow plastic film with tapes of thin magnetizable coating. It is essentially a device which records or perhaps plays back video and audio using magnetic tape, examples of which are tape recorders and video tape recorders.
3. Hard disk Drive
A hard disk drive (HDD) is a non-volatile computer storage device containing magnetic disks or platters rotating at high speeds. It is a secondary storage device used to store data permanently, random access memory (RAM) being the primary memory device. Non-volatile means data is retained when the computer is turned off.
A hard disk drive is also known as a hard drive.
4. Winchester Disk
An early removable disk drive from IBM that put the heads and platters (disks) in a sealed unit for greater speed. Before the Winchester architecture, removable disks were like removable disks today, in which the read/write heads remain in the drive and make contact with the platter after the cartridge is inserted.
5. Pen drive
A pen drive, or a USB flash drive, is a portable data-storage device. Pen drives have replaced the floppy drives of old and have become the most popular data-storage devices among consumers. Micro, lightweight and handy, a pen drive can be easily carried from place to place by students, professionals, academicians and independent tech consultants. Currently available pen drives with storage capacities ranging from 8GB and 32GB can be used to store graphics-heavy documents, photos, music files and video clips.
6. Optical Disk (Optical Memory)

Optical memory uses light beam for its operation. It is developed in fourth generation of computer. It is mainly used for storing audio/video, backup as well as for carrying data. It requires optical drive for its operation. Its read/write speed is slower compared to hard disk and flash memories.
Example: CD, DVD, BD

CD
It stands for Compact Disk. It has storage capacity of 700 MB or approximately 90 minutes of standard audio. CD contains hard circular plastic, single side of this plastic is coated by aluminum alloy. This alloy stores data. It is protected by additional thin plastic covering. CD required CD drive for its operation. Types of CD are:
CD-R is a blank CD in which data can be stored once. After storing data it is converted into CD-ROM.
CD-ROM
It cannot be erased or updated
CD-RW
It is an optical disk stands for compact disk re-writeable. it can be erased and used for multiple times.
DVD
It stands for Digital Versatile Disk. It has the storage capacity of 4.7GB to 17GB. Its shape and size is similar to CD but the difference in storage capacity is due to different chemical component and data is compressed before storing. It requires DVD drive for its operation. Read/write speed of DVD is slower than that of CD. Types of DVD are:
DVD-R
DVD-ROM
DVD-RW
DVD can also be classified as:
Single sided single layered DVD (4.7GB)
Single sided dual layered DVD (7-8GB)
Dual sided single layered DVD (9GB)
Dual sided dual layered DVD (17GB)
BD
It stands for Blue ray disk. It has the storage capacity of 25GB-50GB. It requires BD drive for its operation. Its shape and size is similar to CD and DVD. Types of BD are:
BD-R
BD-ROM
BD-RW
Working mechanism of CD
The surface of the CD contains land and pit. Land represents binary 1 and pit represents binary 0. During CD reading process a beam of light is emitted which strikes the surface of CD and gets reflected. The reflection is captured by lens in the CD drive. Difference in reflection from land and pit is identified to determine 1 and 0. Land is actually in a crystalline form and pit is in amorphous form. The size of land and pit is smaller in DVD compared to CD.
External memory devices:
• Zip disk
It is a magnetic memory. It is thee modification of floppy disk. It has the storage capacity of 100MB and 250MB. It requires Zip disk drive for its operation.

• Jaz disk
It is also a magnetic memory. It has the storage capacity of 2GB. It also requires separate Jaz disk drive for its operation.

• Super disk
It is also a magnetic memory. It has the storage capacity of 120MB. It requires Super disk drive for its operation. Both floppy and super disk can be used in super disk drive.

• Pen drive
It is a flash memory. It is a semi-conductor memory. It is mainly used for transferring data. It has faster read/write speed compared to magnetic memory. Pen drive has storage capacity of few MB-GB. A pen drive is a plug and play device. A pen drive can be connected with the computer through USB port.

4. What are output device? Explain in details.

Output Device
Those devices which are used to display result after processing in a human understandable language either in hardcopy form or softcopy form is known as output device. Example: Monitor, Printer, Plotter, Speaker and projector, etc.

Soft copy: The result or information which are not permanent and produce by using monitor, speaker, projector. It can be edited and deleted as required.
Monitor
It is also known as VDU (Visual Display Unit). It is the most basic output device. It is used to display the output. Types of monitor on the basis of color display are:

1. Monochrome monitor
It is a single colored monitor. It can display only text and images of a single color against a contrasting background. The first monitor displayed text and images of light green color against black background.
2. Gray scale monitor
It can display 256 different variations of black and white color. It can also display video. The first television set was gray scale.
3. Color monitor
It can display 16-42 million colors. It uses 3 basic colors Red, Blue and Green. All the other colors are the combination of these colors. Color monitor is also known as RGB monitor.
Types of monitor on the basis of architecture:
4. CRT Monitor
CRT is the large bulky sized monitor. It has high power requirement so it is not appropriate for portable devices. It is cheaper and has better brightness so, it is preferred by graphic designers.
Merits of CRT monitor are:
Ø It has better brightness.
Ø It is cheaper in cost.
Ø It is more durable.
Ø It has better graphics and larger viewing angle (~180)

De-merits of CRT monitor are:

Ø Due to its high brightness human eyes are negatively affected.
Ø It requires high power.
Ø It is large in size so occupies more space.
Ø It is not portable.
5. Flat panel monitor
a. LED
LED contains multiple small bulbs. The contents are displayed by turning the bulbs “on” and “off”. Initially it was used only for simple digital displays like in calculator, digital watch, etc. At present it is also used in television, desktop PC, laptop, etc.
Merits of LED are:
Ø It is light in weight so, it can be used in portable devices.
Ø It requires less power.
Ø It is small in size.
Ø Its viewing angle is larger compared to LCD.

De-merits of LED are:

Ø It has low brightness but is better than LCD and plasma.
Ø It is expensive compared to CRT.
Ø It is difficult to maintain.
b. LCD
LCD contains liquid crystals in between two plates of the screen. The plates are made by either glass or plastic. The front plate is transparent and the back plate is reflective. Liquid crystals are charged electronically to display the content. This monitor is popular for portable devices because of its small size, light weight, low power requirement however it has low brightness and it requires viewing angle of almost 90.
Merits of LCD:

Ø It is small in size.
Ø It is light in weight.
Ø It has low power requirements so, can be used in portable devices.
Ø It is cheaper than LED and plasma display.

De-merits of LCD:

Ø It has low brightness.
Ø It is expensive compared to CRT.
Ø It requires viewing angle of almost 90.

c. Plasma display
It contains neon gas in between the two plates of the screen in place of liquid crystals of LCD. It has larger viewing angle but is expensive than LCD. It is smaller in size, light in weight and it has low power requirement and low brightness.
Merits of plasma display:
Ø It is smaller in size and light in weight.
Ø It has low power requirement so can be used in portable devices.
Ø It has larger viewing angle.

De-merits of plasma display:

Ø It has low brightness.
Ø It is expensive than LCD.
Working mechanism of CRT:
A monochrome CRT contains single electron gun which emits beam of electrons. These electrons are attached towards positive phosphorous screen. When an electron strikes the screen it glows and emits light. A small area in which an electron strikes is known as pixel. To display a screen all the pixel are striked by electrons. Accelerating anode varies the speed of the electron and deflecting system changes the path of the electron.
A color CRT monitor contains three electron guns which emits three electrons at a time. These electrons converge in the same pixel to display a color.
Speaker:
Speaker is a soft copy output device for audio. It generates analog sound wave from stored digital sound by using vibrators. Different types of speakers vary on the loudness of sound generated. Some of the speakers used are:
• Ear phone
• Head phone
• Normal speaker
• Woofer
• Loud speaker
Hard copy output devices: The output device which are permanent and displays by printer and plotter. It can’t be altered and deleted.
• Printer
Printer makes the permanent impression of color on the printing material like paper, plastic, clothes, rubber, metal, etc. A printer can be single or multi-colored. Types of printer are:

Ø Impact printer
It prints by physically touching the printing material. It is noisier, slower for printing, single colored. It produces low quality output. It is usually cheaper and it can produce multiple copies at the same time by using carbon paper. It uses ink ribbon for printing.

Example:
• Dot matrix printer
• Daisy wheel printer
• Line printer
Dot matrix printer
• It is an impact type character printer. It prints character by the combination of dots where each dot is printed when the hammer strikes the printing material. It can print both image and text of different font and size. It is appropriate for low volume printing. It is usually available in three operating modes: fast, medium and slow. Faster speed will have low printing quality.
• Merits:
• It can print both image and text of different font and size.
• Its operating cost is low.
• It can print multiple copies at the same time using carbon paper.
•
• De-merits:
• It is noisy, slower.
• It has low printing quality.
• It can print single color only.
• It is not appropriate for large volume printing.
 Daisy wheel printer
• It is an impact type character printer. It can only print text of fixed size and font. It contains separate hammer for each character so it is also know as letter quality printer. Its printing quality is better than dot matrix printer. It is faster than dot matrix printer. It is rarely used at present.
• Merits:
• Its printing quality is better than dot matrix printer.
• It is faster than dot matrix printer.
• It can print multiple copies at the same time using carbon paper.
•
• De-merits:
• It can print text of fixed size and font.
• It is noisy, slower than non-impact printers.
• It has low printing quality than non-impact printers.
• It can print a single color.
• It is not appropriate for large volume printing.
• It can’t print images.
Non impact printer
it prints without touching the printing material. It sprays liquid or powder ink. It uses electromagnetic or electrostatic mechanism. It is noiseless, faster for printing usually expensive, it has high printing quality, it can be single or multi-colored, it cannot produce multiple copies at the same time.

Example: ink jet printer
It is non impact type character printer. It uses liquid ink for printing. It can be single or multi-colored. Multi-colored ink jet printer can use either RGB colors or CYMK (cyan, yellow, magenta, black). This printer uses dot-matrix approach for printing i.e. a dot is formed by spraying liquid ink. Series of dots are used tp print characters and images. It is cheaper to buy but its operating cost is expensive due to expensive ink. So, it is appropriate only for low volume printing.
Merits:
- It is not noisy and is faster than impact printers.
- It can be both single and multi-colored.
- It is cheaper to buy.
- It can print both text and images.
- Its printing quality is better than impact printers.

De-merits:
- Its operating cost is high.
-It is appropriate for low volume printing only.
- It can’t produce multiple copies at the same time.
-It is not appropriate for continuous printing.

laser printer
It is non-impact type page printer. It uses powder ink (toner) for printing. It is expensive to buy but its operating cost is low. So, it is appropriate for large volume printing. Multi-colored laser printer is larger in size and they are slower and expensive. It can print about 30 pages per minute.
Merits:
- It is not noisy and is faster than impact printer.
- It can be both single and multi-colored.
- Its operating cost is low.
-It can print both text and images.
- Its printing quality is better than impact printer.

De-merits:
v It is expensive to buy.
v It can’t print multiple copies at the same time.
It is not appropriate for continuous printing.

Thermal wax printer.
Printer can also be classified as:
Ø Character printer
Ø Line printer
Ø Page printer

• Plotter:
It is large sized printer. It is used to plot large maps, designs, advertisements, etc. It is multi-colored, slow for printing, expensive and large in size. Paper, plastic (mainly flex) is used as printing material. It uses technology like ink jet technology, color pen technology. Ink jet technology uses liquid ink whereas color pen technology uses multi colored pens controlled by the mechanical arm. Ink jet is cheaper and color pen has better printing quality. Different plotters in use are:
Ø Drum plotter
Ø Flat bed plotter

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