Unit 1 introduction to computer Definition: Definition: Computer is an advanced electronic device that takes raw data as input from the user and processes these data under the control of set of instructions (called program) and gives the result (output) and saves output for the future use. It can process both numerical and non-numerical (arithmetic and logical) calculations. Electronic machine operating under the control of instructions stored in its own memory. Thus computer performs following operation. 1. It receives data & instructions from the input device. 2. Processes the data as per instructions. 3. Provides the result (output) in a desired form. Data: Data: It is the collection of raw facts, figures & symbols. Ex : Names of students and their marks in different subjects listed in random random order. Information: Information: It is the data that is processed processed & presented in an organized organized manner. manner. Ex: When the names of students are arranged in alphabetical order, total and average marks are calculated & presented in a tabular form, it is information. Program : Set of instructions that enables enables a computer to perform perform a given task. Advantages of computers/ computers/ Basic Basic characteristic characteristic of computer We see computer everywhere: at home, in school, in the hospital, in the bank, in bookstores and department stores, at recreation centers and in man other places. Computers are the foundation of business, travel, and leisure life today. It is becoming a child's learning tool. It performs logical operations (like adding and subtracting, multiplying and dividing ) and complex functions like algebra through a series of instructions called an algorithm. It is an efficient tool in analyzing and solving problems which involve decisions. 1. High speed: It can solve a complex calculation which takes a long time to complete manually at a few second. It can solve certain classes of arithmetic problems millions of times faster than a skilled mathematician. They can perform millions of calculations in seconds. 2. Accuracy: 2. Accuracy: A computer is faster and helps us complete our work without any mistakes/ errors. 3. Storage: Computers can store large amount of information. Any item of data or any a ny instruction stored in the memory can be retrieved by the computer at lightning speeds. 4. Automation: 4. Automation: Computers can be instructed to perform complex tasks automatically ( which increases the productivity). 5. Diligence: it is capable of doing the repetitive operations thousands of times task repeatedly & with the same accuracy without becoming bored, tired or even e ven careless. 6. Versatility: Computers are flexible to perform both simple and complex tasks. 7. Cost effectiveness: Computers reduce the amount of paper work and human effort, thereby reducing costs. Limitations of computers: No IQ: Computers need clear & complete instructions to perform a task accurately. If the instructions are not clear & complete, the computer will not produce the required result. Computers cannot learn by experience. No Feeling: - It does not have feelings or emotion, taste, knowledge and experience. A computer cannot generate information on its own. A computer cannot correct wrong instruction. If a computer is fed with incorrect instructions or data, whether intentionally will produce wrong information. A computer cannot replace a human brain. It cannot think on its own and works only on stored procedures. You cannot depend on the computer every time. It is subject to occasional breakdown. Like any machines, a computer malfunctions due to power fluctuations or worn out sto rage devices and other components.
Classification of Computers Computers are classified according to the storage capacity, speed and the purpose for which they are developed. These can be classified classified into three types: 1. Analog Computes 2. Digital Computers 3. Hybrid Computers 1. Analog computers: They operate by measuring instead of counting. The name (derived from Greek word analog) denotes that the computer functions by establishing similarities between the two quantities. They are powerful tools for solving differential differential equations. 2. Digital Computers: Computers: These computers operate by counting. All quantities are expressed as discrete digits or numbers. numbers. These are useful for evaluating arithmetic expressions and manipulations of data. 3. Hybrid Computers: Computers which combine the features of analog and digital computers are known as Hybrid computers. A majority of the computers computers that are in use are digital. digital. These computers were essentially developed for computations. Later, the developments in the computers led to the use of digital computers in variety of applications. Depending on the use of applications, the digital computers are classified into 1) Special Purpose Computers and 2) General Purpose Computers 1. Special Purpose Computers: These are developed with with a specific purpose. Some of the areas where these computers are being used are – soil testing, drip irrigation, medical scanning, traffic signals, spacecraft, rocket technology etc., 2. General Purpose Computers: Computers : These are developed to meet the requirements of several areas such as simulation, solving mathematical equations, payroll and personnel database. These computers are available in different sizes and capabilities.
Depending on the size the computers are classified into following groups a) Super Computers b) Mainframe Computers c) Mini Computers d) Micro Computers a) Super a) Super Computers: Computers: These have extremely large storage capacities and computing speeds which are at least 10 times faster than other computers. computers. These are used for large scale numerical problems in scientific and engineering engineering disciplines such as electronics, electronics, weather forecasting etc.,. The first super computer was developed in U.S.A. by CRAY computers. In India the indigenous super computer computer was developed under under the name Param. b) Mainframe Computers: Computers: They also have large storage and high computing speed (but relatively lower than the super computers). They are used in applications like weather forecasting, space applications etc., they support a large number of terminals for use by a variety of users simultaneously, but are expensive c) Mini Computers: Computers: It is a medium sized computer with moderate cost, available indigenously and used for large volume applications. applications. It can serve multi-users multi-users simultaneously d) Micro Computers: Computers: A microcomputer is is the smallest general purpose processing processing system. Micro computers are also referred as ―personal computers‖ (PC). These are self contained units and usually developed for use by one person at a time but can be linked to very large systems. They are cheap, easy to use even at homes and can be read for variety of applications from small to medium range. These are available available in three models: 1. PC : Personal Computer Computer 2. PC-XT : PC with Extended Technology 3. PC-AT : PC with Advanced Technology
PERSONAL COMPUTERS Personal Computer: A personal computer is a computer small and low cost, which is intended for personal use (or for use by a small group of individuals). The term "personal computer" is used to describe desktop computers (desktops). – Desktop Computer: a personal or micro-mini computer sufficient to fit on a desk. Laptop Computer: a portable computer complete with an integrated screen and keyboard. It – is generally smaller in size than a desktop computer and larger than a notebook computer. Palmtop Computer/Digital Diary /Notebook /PDAs: a hand-sized computer. Palmtops – have no keyboard but the screen serves both as an input and output device A personal computer has a Monitor (VDU), a keyboard , Disk Drive (s), printer and CPU. The CPU of PC has a mother board with several chips mounted on a circuit board. The major components of the circuit board are : Microprocessor, RAM and ROM chips and other supporting circuits. Microprocessor: The Microprocessor chip is like a brain of human being which contains circuits and registers to perform arithmetic, logic and control functions. i.e it contains ALU & CU. These chips will be able to retrieve data from the input output devices, store, manipulate and process a byte of data at a time. There is an address bus which is built into these chips to determine the storage locations (of RAM) of the data and the instructions of the program. Over the years, different microprocessors were developed and the first in the series is INTEL 8080. The other processor are 8088, 80286, 80386, 80486, Pentium I, II, III and Pentium 4. The Pentium 4 can execute any piece of code that ran on the original 8088, but it does it about 5000 times faster. Clock Speed: The speed with which the instruction is executed or number of pulses per second is called the clock speed. It is measured in terms of million pulses per second (MHZs). The following table gives the differences among the different processors tha t intel has introduced over the years : S.No.
Microprocessor
Date
Transistors 600
Clock speed
Data width
2MHZ
8 bits
5 MHZ 6 MHZ
16 bits 8-bit bus 16 bits
1
808
1974
2
1979
3
808 8 8028
1982
29,00 0 134,000
4
8038
1985
275,000
16 MHZ
32 bits
5
8048
1989
1,200,000
25 MHZ
32 bits
6
Pentium I
1993
3,100,000
60 MHZ
7
Pentium II
1997
7,500,000
233 MHZ
8
Pentium III
1999
9,500,000
450 MHZ
9
Pentium 4
2000
42,000,000
1.5 GHZ
10
Pentium 4 ―Prescott
2004
125,000,000
3.6 GHZ
32 bits 32 bits 32 bits 32 bits 32 bits
Peripherals: The input, output and secondary storage units like floppy drives, keyboard, mouse, etc., are called peripherals. Classification of PCs: PCs are mainly classified on the basis of primary memory (RAM), Microprocessor, clock speed and peripherals. The classification is presented in the following table:
Generations of computers: Generation First Generation (1940-1956 )
Component used Vacuum tubes
Second Generation (1955-1963)
Transistors
Third Generation (1964-1971 )
Integrated Circuits (IC)
Fourth Generation ( 1971-present)
Very Large Scale Integrated Circuits (VLSI) microprocessor
Fifth Generation (present to beyond )
Ultra Scale Integrated Circuits (ULSI) Micro Processor (SILICON CHIP) artificial intelligence
First generation • The first computers used vacuum tubes for circuitry and magnetic drums for memory. • Very expensive, Large sized taking up entire rooms. • Using a great deal of electricity, generated a lot of heat, which was often the cause of malfunctions. • The lowest-level programming language understood by computers. • The processing speed was measured in terms of the millisecond. • The UNIVAC, EDVAC and ENIAC computers are examples of first-generation computing devices. • The UNIVAC was the first commercial computer delivered to a business client, the U.S. Census Bureau in 1951. • Note:- Vacuum tube was developed by the Lee Deforest in 1908. Second generation • Transistors replaced vacuum tubes in the second generation of computers • Transistors were developed by the John Bardeen and his co-worker. • Transistor make the computer smaller, faster, cheaper, more energy-efficient than their firstgeneration predecessors. • Processing speed were measured in terms of microsecond. • punched cards and printouts. • Early versions of COBOL and FORTRAN late version IBM 1401 HP 150II Third generation • The development of the integrated circuit(IC) Robert Noyce and his friends. • Smaller, less heat producing, consume less power. • Speed measured in nano-second • generation computers through keyboards and monitors and interfaced with an operating system, which allowed the device to run many different applications at one time with a central program. • Magnetic disk were used as secondary storage devices. • UNIVAC, and HP2100. Fourth generation • The Microprocessor brought the fourth generation of computers, as thousands of integrated circuits were built onto a single silicon chip. LSI (Large scale IC) a nd VLSIC used
The use of parallel processing and superconductors is helping to make artificial intelligence a reality Initiated in japan Use of Ultra large scale integrated circuits No of CPU are added for better performances Prolog (program logic) and mercury will be used. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization. History of the computer With the need of counting Prehistoric man uses Pebbles, and bones of dead animals. Later on it was replaced by sticks and then by fingers then attempts to develop machines to do fast calculation. Brief summery • Chinese abacus • Napier’s bones 1617 • Slide rule 1620 • Blaise Pascal (approx. 1650) • J.M. Jacquard (early 1800’s) • Charles Babbage difference Engine 1822 and Analytical engine 1833 AD • Lady Augusta Ada • Herman Hollerith(1890 census) • Early Electronic Computers ABC Computer in 1937 Mark –I computer 1937-1944 ENIAC-1946 EDVAC-1946 EDSAC-1949 UNIVAC-1946 Chinese abacus • First machines • Made of Wooden frame with rod having beads. • There is cross bars that separated the beads in each of the wires. • Upper parts heaven ( each beads have numeric value 5 ) lower 5 beads with the value 1 it is called earth • The beads are counted by the moving them up or down towards the crossbars.
Napier’s bones • Napier's bones is an abacus created by John Napier for calculation of multiplication, division, root square etc • A set consists of 10 rods corresponding to digits 0 to 9.
Slide rule 1620
• •
In 1671, Gottfried von Leibnitz, a German mathematician designed this It can do addition, subtraction, multiplication, division and even fine square root.
J.M. Jacquard (early 1800’s) • Developed loom that used punched cards (the equivalent of stored programs) Punched cards • Information coded on cards (forerunner of • Modern storage devices) • Cards could be linked in a series(forerunner of programs) • Such programs can automate human tasks Charles Babbage • British scientist and inventor • known as ‘the Father of the Computer’ • His machine is called difference Engine 1822 AD • Could compute and print tables but never got out of the 'working prototype' stage because of technological limits Babbage’s purposed an analytical engine in 1833 AD • Steam powered calculating machine using programs on punched cards. • The analytical engine was never completed in his lifetime due to financial problems Analytical Engine • Contained all the elements of Modern computers including • 'mill' (for calculating) • 'store' (for holding instructions) • 'operator' (for carrying out instructions) • reading and writing device
• • • • •
Lady Augusta Ada Lord Byron’s daughter Mathematician Devised way to use punched cards to give instructions to Babbage’s machines The ‘first computer programmer’ She is considered as the first computer programmer for devising suitable binary number systems for writing programs.
Herman Hollerith(1890 census) • American census statistician • Invented a tabulating machine using punched cards (same size as ours today). • Founded forerunner of IBM ( international Business Machines Corporation) Early Electronic Computers • ABC Computer in 1937 Dr. John V. Atanasof and Clifford Berry It is considered to be first electrical digital computer. Use electronic vacuum tubes • Mark I Electromechanical computer
Micro processor
ANATOMY OF COMPUTERS/ COMPUTER ARCHITECTURE The computer system consists of three units:
CENTRAL PROCESSING UNIT
INPUT DEVICE
OUT PUT DEVICE Monitor, Printer, Speaker
Keyboard Mouse Scanner MICR, Web camera Microphone
The various functions of these units can be summarized as:
Unit 1. Input device
Function : Reads information from input media and enters to the computer in a coded form
2.CPU (a) Memory unit (b) Arithmetic Logic unit (c) Control Unit 3. Output device user
: Stores program and data : Performs arithmetic and logical functions : Interprets program instructions and controls the input and output devices : decodes information and presents it to the
Central Processing Unit : It is the part of the computer that carries out the instructions of a computer program. It is the unit that reads and executes program instructions. Hence it is known as the brain of the computer. The CPU consists of storage or memory unit, Arithmetic Logic Unit (ALU) and control unit. (a). Memory Unit: It is also known as the primary storage or main memory. It stores data, program instructions, internal results and final output temporarily before it is sent to an appropriate output device. It consists of thousands of cells called ―storage locations‖. These cells activate with ―off-on‖ or binary digits(0,1) mechanism. Thus a character either a letter or numerical digit is stored as a string of (0,1) Binary digits ( BITS). These bits are used to store instructions and data by their combinations.
(c).Control Unit : It acts as a central nervous system and ensures that the information is stored correctly and the program instructions are followed in proper sequence as well as the data are selected from the memory as necessary. It also coordinates all the input and output devices of a system. Input Devices Devices used to provide data and instructions to the computer are called Input devices. Some important input devices are Key board, Mouse, Scanner, MICR, Web camera, Microphone etc. 1. Keyboard : The Key board is used for typing text into the computer. A computer keyboard is similar to that of a type writer with additional keys. The most commonly available computer keyboard has 104 keys. There are different types of keys on the keyboard. The keys are categorized as: Alphanumeric keys, including letters & numbers. o o Punctuation keys, such as colon (:), semicolon (;) Question mark (?), Single & double Quotes (“”) o Special keys such as arrow keys, control keys, function keys (F1 to F12), HOME, END etc. 2. Mouse: It is a device that controls the movement of the cursor on a monitor. A mouse will have 2 buttons on its top. The left button is the most frequently used button. There will be a wheel between the left and right buttons. This wheel enables us to smoothly scroll through screens of information. As we move the mouse, the pointer on the monitor moves in the same direction. Optical mouse is another advanced pointing device that uses a light emitting component instead of the mouse ball. Mouse cannot be used for entering the data. It is only useful to select the options on the screen. 3. Scanner: : It is an input device that can read text or illustrations printed on paper and translate into digital form. The main advantage of these scanners is that the data need not be entered separately resulting in saving lot of time.
Scanners are of two types: i) optical scanners
ii) MICR
i) Optical scanners: a. Optical character Recognition (OCR): OCR is an input device used to read a printed text. OCR scans text optically character by character, converts them into a machine readable code and stores the text on the system memory. b. Optical mark recognition(OMR): OMR is a special type of optical scanner used to recognize the type of mark made by pen or pencil. It is used where one out of a few alternatives is to be selected and marked. It is specially used for checking the answer sheets of examinations having multiple choice questions C. Optical barcode recognition(OBCR): Barcode readers are photoelectric scanners that read the bar codes or vertical zebra striped marks printed on product containers. This is used in super markets, book shops etc.
A light pen can work with any CRT-based display, but not with LCD screens (though Toshiba and Hitachi displayed a similar idea at the "Display 2006" show in Japan [1]), projectors and other display devices. 6. Joystick A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. 7. Track ball Essentially, the trackball is an upside-down mouse that rotates in place within a socket. The user rolls the ball to direct the cursor to the desired place on the screen and can click one of two buttons (identical to mouse buttons) near the trackball to select desktop objects or position the cursor for text entry.
8. Touch screen A touchscreen is an electronic visual display that the user can control through simple or multi-touch gestures by touching the screen with one or more fingers. 9. Voice recognition In computer science, speech recognition (SR) is the translation of spoken words into text. 10. Digital camera A digital camera (or digi cam) is a camera that encodes digital images and videos digitally and stores them for later reproduction. 11. Digitizing tablets Digitizer is an input device, which converts analog information into a digital form. Digitizer can convert a signal from the television camera into a series of numbers that could be stored in a computer. They can be used by the computer to create a picture of whatever the camera had been pointed at. Digitizer is also known as Tablet or Graphics Tablet because it converts graphics and pictorial data into binary inputs. A graphic tablet as digitizer is used for to hand-draw images and graphics, similar to the way a person draws images with a pencil.
Output devices
Any device that is capable of representing information on a computer is calle d an Output device. Output devices receive information from the CPU and present it to the user in the desired form. Some important Output devices are : Monitor, Printer
1 .Terminal/Monitor: • Monitors are used to view your data on a computer. It is also referred as Visual Display Unit(VDU). • It is similar to TV screen- either a monochrome (black & white) or colour – and it displays the output. • Information on a display device sometimes is called soft copy. Characteristic of the monitor
C) Dot Pitch: It is a measurement that indicates the vertical distance between each pixel on a display screen. It is measured in millimeter. The dot pitch is one of the principle characteristics that determine the quality of display monitors.
Type of monitor A) Analog and digital analog technologies record waveforms as they are, while digital technologies convert analog waveforms into sets of numbers, recording the numbers instead. B) CRT monitor Large sealed, glass screen. Screen coated with tiny dots of phosphor material. D) LCD monitor Type of flat-panel display Uses liquid crystals between two sheets of material to present information on screen. Electric current passes through crystals, which creates images on the screen. Where are some features of LCD screens? • Lightweight and compact • Consumes less than one-third of the power than does a CRT monitor • Ideal for notebook and handheld computers
E) Gas plasma monitor Flat-panel display uses layer of gas plasma between two sheets of material Larger screen sizes and higher display quality than LCD, but much more expensive. Pixel ( picture element)
• • • •
Screen of CRT monitor is coated with tiny dots of the phosphor material. Three dots (red, blue, and green) combine to make up each pixel. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels One mega pixel is equals to 1 million pixels.
C) Dot pitch • Measure of the distance between pixels Sometimes called pixel pitch • Smaller the distance between the pixels, the sharper the image D) Refresh rate • The refresh rate determines how many times per seconds the screen is to be red drawn. The refresh rate of a monitor is measured in Hertz. The faster the refresher is, the less the monitor flickers. • High-quality monitor will provide refresh rate of at least 75 hertz. • Image on the screen redraws itself 75 times per second. E) Band width The amount of data that can be transmitted in a fixed amount of time for digital devices, the band width is usually expressed in bits or bytes per second (bps). For analog devices it is expressed in cycle per second or Hertz (Hz).
2. Printer: A printer is used to transfer data from a computer onto paper. The paper copy obtained from a printer is often referred as follows: S. No.
Type
Print out.
The different printers and their speeds are as
Mode of Printing
Speed
Dot – Matrix
Prints the character in dotted pattern 200/300 to 700
Printer
through printer ribbon using either 24 pin or 9 pin
CPS
2
Ink Jet printer
Work by spraying ionized ink
Slow, 90 CPS
3
Laser printer
Also called page printer. Uses laser beam to produce an image.
6 to 12 PPM
4
Line printer
Prints lines at a time instead of single 300 to 600 LPM characters.
5
Plotter
Produces drawings or graphs through pens which are filled with different colors.
1
( CPS: Characters Per Second; PPM: Pages Per Minutes; LPM : Lines Per Minute)
Laser printer
MEMORY OF THE COMPUTER
•
A memory is just like a human brain. It is used to store data and instruction. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. • The memory is divided into large number of small parts. Each part is called cell. Each location or cell has a unique address which varies from zero to memory size minus one. • For example if computer has 64k words, then this memory unit has 64 * 1024=65536 memory location. Any storage unit of a computer system is classified on the basis of the following criteria: 1. Access time: This is the time required to locate and retrieve stored data from the storage unit in response to program instructions. 2. Storage capacity: It is the amount of data that can be stored in the storage unit. 3. Cost per bit of storage. Units of memory: The computer stores a character in the storage cells with binary (0,1) mechanism. Thus the basic unit of memory is a bit (binary digit – 0,1). To store a character, a computer requires 8 bits or 1 byte. This is called the ― word length‖ of the storage unit. Hence the storage capacity of the computer is measured in the number of words it can store and is expressed in terms of bytes. The different units of measurement are 8 Bits
=
1 Byte
210 (or) 1024 Bytes = 1 Kilo Byte (KB) 210 (or) 1024 KB 210 (or)1024 MB
= 1 Mega Byte (MB)
= 1 Gega Byte (GB) Conversion :
ASCII – American Standard Code for Information interchange.
This code has given alphabets like some numbers which can be converted to Binary form. A- 65 …….Z – 90 and a – 97 ………. z – 121 By using these codes the alphabets can be converted to digital & hence to Binary form.
Types of Memory : A computer memory is of two types 1. Primary Memory ( Internal storage) Cache memory
2. Secondary Memory (External storage) 3.
Primary Memory : Primary memory is also called internal memory and is an important part of a computer. It is the main area in a computer where the data is stored. The stored data can be recalled instantly and correctly whenever desired. This memory can be quickly accessed by the CPU for reading or storing information. This is attached to the motherboard already by the manufacturer.
Primary memory is further classified into two types: Random Access Memory (RAM) and Read- Only Memory (ROM ) RAM: RAM is also known as read/write memory as information can be read from and written onto it. RAM is a place in a computer that holds instructions for the computer, its programs and the data. The CPU can directly access the data from RAM almost immediately. However, the storage of data and instructions in RAM is temporary, till the time the computer is running. It disappears from RAM as soon as the power to the computer is switched off. i.e it is volatile memory.
ROM: It is called Read-only memory as information can only be read from and not written or changed onto ROM. ROM is the built in memory of a computer. It stores some basic input – output instructions put by the manufacturer to operate the computer. The storage of data and instructions in ROM is permanent. It does not depend on the power supply. i.e it is non-volatile memory. Type of ROM 1. PROM PROM is read-only memory that can be modified only once by a user. The user buys a blank PROM and enters the desired contents using a PROM programmer. Inside the PROM chip there are small fuses which are burnt open during programming. It can be programmed only once and is not erasable.
2. Firmware Firmware can be thought of as "semi-permanent" since it remains the same unless it is updated by a firmware updater. ROM chips manufactured with permanently written data, instructions, or information 3 EPROM: (Erasable Programmable Read Only memory) . Enable to remove information or data from EPROM Chips and also reprogrammed to store new information. ( they are erased by using ultraviolet rays or the electricity. Advantages of ROM • Non-volatile in nature • These cannot be accidentally changed • Cheaper than RAMs • Easy to test • More Reliable than RAMs • These are static and do not require refreshing • Its contents are always known and can be verified
Secondary memory: This type of memory is also known as external memory or non-volatile. The primary memory which is faster (and hence expensive) is generally not sufficient for large storage of data. As a result, additional memory, called the ―auxiliary or ―secondary memory is used. It is also referred as ―backup storage as it is used to store large volume of data on a permanent basis which can be transferred to the primary memory whenever required for processing. Data are stored in secondary storage in the same binary codes as in the main (primary memory) storage. Some of the devices of secondary storages are Floppy Disk, Hard Disk, CD-ROM, DVD and Flash drive. 1. Floppy Disk : (Winchester Disk) It is also referred as Diskette: and is made of flexible Vinyl material. It has a small hole on one side called ―Right protect notch, Which protects accidental writing/deleting the information from the disk. There is a hole in the Centre through which the spindle of drive unit rotates the disk. The disks are available in two sizes of 5.25 and 3.5 inches and these could be either low- density or high-density floppies. Storage capacity of floppies are measured in kilobytes (KB) and megabytes (MB). The details about the storage capacities of the floppies are presented below: Floppy Disk Low Density High Density High Density Extended
2. Hard Disk :
Storage Capacity 360 KB 1.2 MB 1.44 MB 2.8 MB
Size (Diameter) 5.25 inches 5.25 inches 3.5 inches 3.5 inches
The hard disk can hold more information than the floppy
disk and the retrieval of information from hard disk is faster when compared to floppies or tapes. A hard disk is fixed inside the CPU and its capacity ranges from 20 MB onwards. The hard disk is made up of a collection of discs (one below the other) known as platters on which the data is recorded. These platters are coated with magnetic material. It is less sensitive to external environmental disorders and hence the storage in hard disk is safe. A small hard disk might be as much as 25 times larger than a floppy disk. Storage Capacity of hard disks varies from 20 MB to several Gega bytes like 80GB, 160GB. 3. CD-ROM: CD-ROM stands for Compact Disk –Read Only Memory. It is used to store a wide variety of information. Its main advantage is that it is portable and can hold a large amount of data.. The storage capacity of most CD-ROMs is approximately 650 MB or 700 MB. CD-ROMs have the following variations: (i) CD-R (Compact disc Recordable): Data can be written onto it just once. The stored data can be read. Data once written onto it cannot be erased. (ii) CD-RW (Compact disc Rewritable): It is also called erasable CD. Data once written onto it can be erased to write or record new information many times. To use a CD-ROM, a device called CD drive is needed.
4. DVD: DVD stands for Digital Versatile Disc. It is similar to a CD-ROM, except that it can store larger amounts of data. The storage capacity of a DVD is at least 4.7MB. DVDs that can store up to 17GBs are also available. Because of their capacity, DVDs are generally used to store a very large multimedia presentations and movies that combine high quality sound and graphics. 5. Flash Drive: It is a small, portable device that can be used to store, access and transfer data. Due to its small size, it is commonly called Pen drive. It is also called USB drive. We can read, write, copy, delete, and move data from computer to pen drive or pen drive to computer. It comes in various storage capacities of 2GB, 4GB, 8GB etc. It is popular because it is easy to use and small enough to be carried in a pocket. This device is plugged into the USB port of the computer and the computer automatically detects this device.
Cache memory • The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. Cache memory is a very high speed semiconductor memory which can speed up CPU. It acts as a buffer between the CPU and main memory. It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them. Short for Level 1 cache, a memory cache built into the microprocessor. i.e. SRAM Short for Level 2 cache, cache memory that is external to the microprocessor DRAM ADVANTAGE • Cache memory is faster than main memory. • It consumes less access time as compared to main memory. • It stores the program that can be executed within a short period of time. • It stores data for temporary use. • The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer, CPU direct communicate with cache. DISADVANTAGE: • Cache memory has limited capacity. • It is very expensive
Computer interfaces What is a Port?
Ports are slots on the motherboard into which a cable of external device like mouse, keyboard, monitor, microphone, speakers, etc. is plugged in.
It connects the external devices into the system unit.
Following are few important types of ports:
Serial Port
Transmits one bit of data at a time. Used to connect slow speed devices, such as mouse, keyboard, modem Two versions: 9 pin, 25 pin models. Data travels at 115 kilobits per second.
Parallel Port
Connects devices that can transfer more than one bit at a time, such as a printer and scanner 25 pin model. Also known as IEEE 1284-compliant Centronics port.
PS/2 Port Used for old computer keyboard and mouse
Also called mouse port.
Most of the old computers provide two PS/2 ports, each for mouse and keyboard.
Also known as IEEE 1284-compliant Centronics port.
Universal Serial Bus (or USB) Port
Can connect all kinds of external USB devices such as external hard disk, printer, scanner, mouse, keyboard, etc. Introduced in 1997.
Most of the computers provide two USB ports as minimum.
Data travels at 12 megabits per second.
USB compliant devices can get power from a USB port.
VGA Port
Connects monitor to a computer's video ca rd.
Has 15 holes.
Similar to serial port connector but serial port connector has pins, it has holes.
Power Connector
Three-pronged plug
Connects to the computer's power cable that plugs into a power bar or wall socket. Fire wire Port
Transfer large amounts of data at very fast speed.
Connects camcorders and video equipments to the computer
Data travels at 400 to 800 megabits per second.
Invented by Apple
Three variants: 4-Pin FireWire 400 connector, 6-Pin FireWire 400 connector and 9-Pin FireWire 800 connector Modem Connects a PC's modem to the telephone network. Ethernet Port
Connects to a network and high speed Internet.
Connects network cable to a computer.
This port resides on an Ethernet Card.
Data travels at 10 megabits to 1000 megabits per second depending upon the network bandwidth. Game Port Connect a PC to a joystick. Now replaced by USB. Digital Video Interface, DVI port Connects a Flat panel LCD monitor to the computer's high-end video graphic cards. Very popular among video card manufacturers. Sockets Connect microphone, speakers to sound card of the computer
Buses of computer Bus is a communication system that transfers data between components inside a computer , or between computers. This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocol.
It may be parallel or serial Parallel data buses carry data on many wires simultaneously. Each wire, or path, as they are sometimes called, carries one bit of data. The most common parallel buses found in computers today are the ATA, which stands for Advanced Technology Attachment; the PC card, which stands for personal computer and is used in laptops, and the SCSI, or Small Computer System Interface A serial data bus has one wire or path, and carries all the bits, one after the other. The most common serial data buses include the USB, also known as the Universal Serial Bus; FireWire; Serial ATA; and Serial Attached SCSI. Classification of buses
System bus (internal bus) The bus that connects the CPU to main memory on the motherboard. ( RAM or ROM) The system bus is also called the front-side bus, memory bus, local bus, or host bus.
Expansion bus (external buses)
connecting various peripheral devices to the CPU These are connected to the system bus via a ‘bridge’ implemented in the processors chipset. They are: 1. Address buses: these buses carry address given by the CPU from one unit to another in the computer. 2. Data buses: These buses carry data from one unit to other, it is a bi-directional bus i.e the data can be carried in both directions. 3. Control buses: These buses carry control signal from ALU to memory and from memory to alu and then to the output unit.
Unit 2 Computer hardware and software Hardware : Hardware represents the physical and tangible components of the computer, i.e., the components that can be seen and touched. examples of Hardware are following:
Input devices -- keyboard, mouse, etc. Output devices -- printer, monitor, etc. Secondary storage devices -- Hard disk, CD, DVD, etc. Internal components -- CPU, motherboard, RAM, etc.
Software : Software is a program or set of instructions that causes the Hardware to function in a desired way. There are five categories of software. They are: 1. Operating System 2. Translators 3. Utility programs 4. Application programs 5. General purpose programs
Operating system Set of programs that coordinate all activities among compute r hardware resources.Operating system resides on hard disk in most cases. But after opening computer it is loaded in the RAM. Function of operating system The computer understanding language and human understanding language are different hence the operating system acts as interface between the hardware and the user programs and facilitates the execution of programs i.e. it is a bridge between the user and the Hardware. Start up the computer Administer security Control a network access the Web Monitor performance( error detecting ) and provide housekeeping services Schedule jobs and configure devices Manage processor, memory, programs, input/out put devices, file, provide user interface Establishment and enforcement of a priority system : It determines and maintai ns the order in which jobs are to be executed in the computer system
Type of the operating systems Multitasking Allows single user to work on two or more applications that reside in memory at same time. Multiuser Operating system enables two or more users to run a program simultaneously
Multiprocessing Operating system can support two or more processors running programs at same time The User interface provided by the OS can be character based or graphical. CUI: (Character user Interface):- It is operated with keyboard only. Ex: MS-DOS, UNIX GUI: (Graphical user Interface):- The system can be operated with mouse and keyboard. Ex: Windows 95, Windows XP etc. Disk Operating System (DOS): Dos is a single user and single task operating system it was developed as early as 1980 by Bill Gates at the age of 19. It is suited for personal computers. WINDOWS operating systems : It works with DOS and it supports single user and multitask system. It requires a powerful PC with a minimum RAM of 8 MB. UNIX AND XENIX: It is suited for multi-user and multi-task system
