The development of electronic computers can be divided into five generations depending upon the technologies used. The following are the five generations of computers.

First Generation of Computers (1942-1955)

Image Courtesy: www.computerhistory.org

The beginning of commercial computer age is from UNIVAC(Universal Automatic Computer). It was developed by two scientists Mauchly and Echert at the Census Department of United States in 1947. The first generation computers were used during 1942-1955. They were based on vacuum tubes. Examples of first generation computers are ENIVAC and UNIVAC-1.

Advantages

• Vacuum tubes were the only electronic component available during those days.
• Vacuum tube technology made possible to make electronic digital computers.
• These computers could calculate data in millisecond.

Disadvantages

• The computers were very large in size.
• They consumed a large amount of energy.
• They heated very soon due to thousands of vacuum tubes.
• They were not very reliable.
• Air conditioning was required.
• Constant maintenance was required.
• Non-portable.
• Costly commercial production.
• Limited commercial use.
• Very slow speed.
• Limited programming capabilities.
• Used machine language only.
• Used magnetic drums which provide very less data storage.
• Used punch cards for input.
• Not versatile and very faulty.

                                Similar Topics:Types of Computers by Purpose  | Types of Printers

Second Generation Computers (1955-1964)

Image Courtesy: www.ibm.com

The second generation computers used transistors. The scientists at Bell laboratories developed transistor in 1947. These scientists include John Barden, William Brattain and William Shockley. The size of the computers was decreased by replacing vacuum tubes with transistors. The examples of second generation computers are IBM 7094 series, IBM 1400 series and CDC 164 etc.

Advantages

• Smaller in size as compared to the first generation computers.
• The 2nd generation Computers were more reliable
• Used less energy and were not heated.
• Wider commercial use
• Better portability as compared to the first generation computers.
• Better speed and could calculate data in microseconds
• Used faster peripherals like tape drives, magnetic disks, printer etc.
• Used Assembly language instead of Machine language.
• Accuracy improved.

Disadvantages

• Cooling system was required
• Constant maintenance was required
• Commercial production was difficult
• Only used for specific purposes
• Costly and not versatile
• Puch cards were used for input.

Third Generation Computers (1964-1975)

Image Courtesy: www.computerhistory.org

The Third generation computers used the integrated circuits (IC). Jack Kilby developed the concept of integrated circuit in 1958. It was an important invention in the computer field. The first IC was invented and used in 1961. The size of an IC is about ¼ square inch. A single IC chip may contain thousands of transistors. The computer became smaller in size, faster, more reliable and less expensive. The examples of third generation computers are IBM 370, IBM System/360, UNIVAC 1108 and UNIVAC AC 9000 etc.

Advantages

• Smaller in size as compared to previous generations.
• More reliable.
• Used less energy
• Produced less heat as compared to the previous two generations of computers.
• Better speed and could calculate data in nanoseconds.
• Used fan for heat discharge to prevent damage.
• Maintenance cost was low because hardware failure is reare.
• Totally general purpose
• Could be used for high-level languages.
• Good storage
• Versatile to an extent
• Less expensive
• Better accuracy
• Commercial production increased.
• Used mouse and keyboard for input.

Disadvantages

• Air conditioning was required.
• Highly sophisticated technology required for the manufacturing of IC chips.

Fourth Generation Computers (1975-Present)

The fourth generation computers started with the invention of Microprocessor. The Microprocessor contains thousands of ICs. Ted Hoff produced the first microprocessor in 1971 for Intel. It was known as Intel 4004. The technology of integrated circuits improved rapidly. The LSI (Large Scale Integration) circuit and VLSI (Very Large Scale Integration) circuit was designed. It greatly reduced the size of computer. The size of modern Microprocessors is usually one square inch. It can contain millions of electronic circuits. The examples of fourth generation computers are Apple Macintosh & IBM PC.

Advantages

• More powerful and reliable than previous generations.
• Small in size
• Fast processing power with less power consumption
• Fan for heat discharging and thus to keep cold.
• No air conditioning required.
• Totally general purpose
• Commercial production
• Less need of repair.
• Cheapest among all generations
• All types of High level languages can be used in this type of computers

Disadvantages

• The latest technology is required for manufacturing of Microprocessors.

Fifth Generation Computers (Present & Beyond)

Scientists are working hard on the 5^th generation computers with quite a few breakthroughs. It is based on the technique of Artificial Intelligence (AI). Computers can understand spoken words & imitate human reasoning. Can respond to its surroundings using different types of sensors. Scientists are constantly working to increase the processing power of computers. They are trying to create a computer with real IQ with the help of advanced programming and technologies. IBM Watson computeris one example that outsmarts Harvard University Students. The advancement in modern technologies will revolutionize the computer in future.

Read The Four Types of Computers where we have discussed SuperComputers, Mainframe,Mini & Micro Computers in detail.

There are three basic kinds of computers. This is based on the hardware structure and the way physical quantities are represented in a computer. The following are the three types.

Analog Computers

Analog computers are used to process analog data. Analog data is of continuous nature and which is not discrete or separate. Such type of data includes temperature, pressure, speed weight, voltage, depth etc. These quantities are continuous and having an infinite variety of values.

It measures continuous changes in some physical quantity e.g. The Speedometer of a car measures speed, the change of temperature

is measured by a Thermometer, the weight is measured by Weights machine. These computers are ideal in situations where data can be accepted directly from measuring instrument without having to convert it into numbers or codes.

Analog computers are the first computers being developed and provided the basis for the development of the modern digital computers. Analog computers are widely used for certain specialized engineering and scientific applications, for calculation and measurement of analog quantities. They are frequently used to control process such as those found in oil refinery where flow and temperature measurements are important. They are used for example in paper making and in chemical industry. Analog computers do not require any storage capability because they measure and compare quantities in a single operation. Output from an analog computer is generally in the form of readings on a series of dial (Speedometer of a car) or a graph on strip chart.

Digital Computers

A Digital Computer, as its name implies, works with digits to represent numerals, letters or other special symbols. Digital Computers operate on inputs which are ON-OFF type and its output is also in the form of ON-OFF signal. Normally, an ON is represented by a 1 and an OFF is represented by a 0. So we can say that digital computers process information which is based on the presence or the absence of an electrical charge or we prefer to say a binary 1 or 0.

A digital computer can be used to process numeric as well as non-numeric data. It can perform arithmetic operations like addition, subtraction, multiplication and division and also logical operations. Most of the computers available today are digital computers. The most common examples of digital computers are accounting machines and calculators.

The results of digital computers are more accurate than the results of analog computers. Analog computers are faster than digital. Analog computers lack memory whereas digital computers store information. We can say that digital computers count and analog computers measures.

Hybrid Computers

A hybrid is a combination of digital and analog computers. It combines the best features of both types of computers, i-e. It has the speed of analog computer and the memory and accuracy of digital computer. Hybrid computers are used mainly in specialized applications where both kinds of data need to be processed. Therefore, they help the user, to process both continuous and discrete data. For example a petrol pump contains a processor that converts fuel flow measurements into quantity and price values. In hospital Intensive Care Unit (ICU), an analog device is used which measures patient's blood pressure and temperature etc, which are then converted and displayed in the form of digits. Hybrid computers for example are used for scientific calculations, in defense and radar systems.

Bit

The smallest unit of data in a computer is called Bit (Binary Digit). A bit has a single binary value, either 0 or 1. In most computer systems, there are eight bits in a byte. The value of a bit is usually stored as either above or below a designated level of electrical charge in a single capacitor within a memory device.

Nibble

Half a byte (four bits) is called a nibble.

Byte

In most computer systems, a byte is a unit of data that is eight binary digits long. A byte is the unit most computers use to represent a character such as a letter, number or typographic symbol (for example, “g”, “5”, or “?”). A byte can also hold a string of bits that need to be used in some larger unit of application purposes (for example, the stream of bits that constitute a visual image for a program that displays images or the string of bits that constitutes the machine code of a computer program).

In some computer systems, four bytes constitute a word, a unit that a computer processor can be designed to handle efficiently as it reads and processes each instruction. Some computer processors can handle two-byte or single-byte instructions.

A byte is abbreviated with a “B”. (A bit is abbreviated with a small “b”). Computer storage is usually measured in byte multiples. For example, an 820 MB hard drive holds a nominal 820 million bytes – or megabytes – of data. Byte multiples are based on powers of 2 and commonly expressed as a “rounded off” decimal number. For example, one megabyte (“one million bytes”) is actually 1,048,576 (decimal) bytes.

Octet

In some systems, the term octet is used for an eight-bit unit instead of byte. In many systems, four eight-bit bytes or octets form a 32-bit word. In such systems, instructions lengths are sometimes expressed as full-word (32 bits in length) or half-word (16 bits in length).

Kilobyte

A Kilobyte (kb or Kbyte) is approximately a thousand bytes (actually, 2 to the 10^th power, or decimal 1,024 bytes).

Megabyte

As a measure of computer processor storage and real and virtual memory, a megabyte (abbreviated MB) is 2 to the 20^th power byte, or 1,048,576 bytes in decimal notation.

Gigabyte

A Gigabyte (pronounced Gig-a-bite with hard G’s) is a measure of computer data storage capacity and is “roughly” a billion bytes. A gigabyte is two to the 30^th power, or 1,073,741,824 in decimal notation.

Terabyte

A Terabyte is a measure of computer storage capacity and is 2 to the 40^th power of 1024 gigabytes.

Petabyte

A Petabyte (PB) is a measure of memory or storage capacity and is 2 to the 50^th power bytes or, in decimal, approximately a thousand terabytes (1024 terabytes).

Exabyte

An Exabyte (EB) is a large unit of computer data storage, two to the sixtieth power bytes. The prefix exa means one billion billion, or on quintillion, which is a decimal term. Two to the sixtieth power is actually 1,152,921,504,606,846,976 bytes in decimal, or somewhat over a quintillion (or ten to the eighteenth power) bytes. It is common to say that an Exabyte is approximately one quintillion bytes. In decimal terms, an Exabyte is a billion gigabytes.

Zettabyte

A Zettabyte (ZB) is equal to one sextillion bytes. It is commonly abbreviated ZB. At this time, no computer has one Zettabyte of storage. It has 1024 Exabytes.

Yottabyte

A Yottabyte is equal to one septillion bytes. It is commonly abbreviated YB. At this time, no computer has one Zettabyte of storage. It has 1024 Zettabytes.

What is File System?

Everything is stored as files in a computer system. The files can be data files or application files. Each operating system has its own way of organizing data internally. The operating system performs this management with the help of a program called file system. The type of file system is used to determine how data and programs are accessed. It also determines the level of accessibility available to users.

The following are the different file systems.

FAT File System

FAT stands for "File Allocation Table". The file allocation table is used by the operating system to locate files on a disk. A file may be divided into many sections and scattered around the disk due to fragmentation. FAT keeps track of all pieces of a file. In DOS systems, FAT is stored after boot sector. The file system has been used since the advent of PC.

Features of FAT File System

Some important features of  the FAT File System are as follows.

Naming convention

• FAT file system used by MS-DOS provides file name of only 8 characters long.
• FAT file system used by Windows 2000 supports long file name. The full path of file including filename can be up to 255 characters long.
• File names can contain any character except “/ \ [] = , ^ ?a “”
• File names should begin with alphanumeric characters.
• File names can contain spaces and multiple periods. The characters after the last period are treated as file extension.

Security

FAT does not support local and folder security. A user logged on a computer locally has full access to the files and folders in FAT partitions of the computer.

Quick Access to files

FAT provides quick access to files. The speed of file access depends on file type, file size, partition size, fragmentation and number of files in a folder.

FAT32 File System

FAT32 is an advanced version of FAT file system. It can be used on drives from 512 MB to 2TB in size. One of the most important features of FAT and FAT32 is that they offer compatibility with operating systems other than Windows 2000 also.

Features of FAT32 File System

FAT32 has the following features.

Partition size

FAT32 increases the number of bits used to address cluster. A cluster is a set of sectors. It reduces the size of each cluster. It supports larger disk (up to 2TB) and better storage efficiency.

Access Speed

FAT32 provides good file access in partition sizes less than 500 MB or greater than 2 GB. It provides better disk space utilization.

NTFS File System

NTFS stands for "New Technology File System".Windows 2000 professional fully supports NTFS. It has the following characteristics.

Features of NTFS File System

The following are some of the main features of NTFS File System.

Naming Conventions

• File names can be up to 255 characters
• File names can contain most characters except “ / \ <> * | :
• File names are not case sensitive

Security

NTFS provides file and folder security. Files and folders are safer than FAT. Security is maintained by assigning NTFS permissions to files and folders. Security is maintained at the local level and the network level. The permissions can be assigned to individual files and folders. Each file or folder in an NTFS partition has an Access Control List. It contains the users and group security identifier (SID) and the privileges granted to them.

Partition Size

The NTFS partition and file sizes are much bigger than FAT partitions and files. The maximum size of an NTFS partition or file can be 16 Exabyte. However, the practical limitation is two Terabytes. The file size can be in the range of 4GB to 64GB.

File compression

NTFS provides file compression of as much as 50%.

High reliability

NTFS is highly reliable. It is recoverable file system. It uses transaction logs to update the file and folders logs automatically. The system also has a great amount of fault tolerance. It means that if transaction fails due to power or system failure, the logged transactions are used to recover the data.

Bad cluster Mapping

NTFS supports bad-cluster mapping. It means that file system detects bad clusters or areas of disk with errors. If there is any data in those clusters, it is retrieved and stored on another area. The bad clusters are marked to prevent data storage in those areas in futre.

Read our article about the difference between FAT and NTFS file system

FAT File system

• It provides no security if the user logs in locally. The file and folder level security permission does not exist.
• It supports only 8 characters long file name.
• It is suitable for a partition disks that is less than 500 MB.
• Partition and file size can be up to 4 GB.
• It supports no file compression.
• Disk can get fragmented thus slowing down the access.
• It is not very reliable since it does not support bad cluster mapping.

NTFS File system

• It provides security for both local and remote users. The security is provided to the level of files and folders.
• It supports 255 characters long file name.
• It is suitable for partition that is greater than 500 MB.
• Partition size can be up to 16 Exabyte.
• It supports file compression.
• It provides lesser possibility of fragmentation.
• It is highly reliable since it supports bad cluster mapping and transaction logging.

Number System

A set of values used to represent different quantities is known as Number System. For example, a number system can be used to represent the number of students in a class or number of viewers watching a certain TV program etc. The digital computer represents all kinds of data and information in binary numbers. It includes audio, graphics, video, text and numbers. The total number of digits used in a number system is called its base or radix. The base is written after the number as subscript such as 512_10.

Some important number systems are as follows.

• Decimal number system
• Binary number system
• Octal number system
• Hexadecimal number system

The decimal number system is used in general. However, the computers use binary number system. The octal and hexadecimal number systems are used in the computer.

Decimal number System

The Decimal Number System consists of ten digits from 0 to 9. These digits can be used to represent any numeric value. The base of decimal number system is 10. It is the most widely used number system. The value represented by individual digit depends on weight and position of the digit.

Each number in this system consists of digits which are located at different positions. The position of first digit towards left side of the decimal point is 0. The position of second digit towards left side of the decimal point is 1. Similarly, the position of first digit towards right side of decimal point is -1. The position of second digit towards right side of decimal point is -2 and so on.

The value of the number is determined by multiplying the digits with the weight of their position and adding the results. This method is known as expansion method. The rightmost digit of number has the lowest weight. This digit is called Least Significant Digit (LSD). The leftmost digit of a number has the highest weight. This digit is called Most Significant Digit (MSD). The digit 7 in the number 724 is most significant digit and 4 is the least significant digit.

 Example:

The weights and positions of each digit of the number 453 are as follows:

 The above table indicates that:

The value of digit 4     =          4x10²   =          400

The value of digit 4     =          5x10    =          50       

The value of digit 3     =          3x10    =          3

The actual number can be found by adding the values obtained by the digits as follows:

400 + 50 + 3    =453₁₀

Example:

The weights and positions of each digit of the number 139.78 are as follows.

The above table indicates that:

The value of digit 1     =          1x10²   =          100

The value of digit 3     =          3x10¹   =          30       

The value of digit 9     =          9x10⁰   =          9

The value of digit 7     =          7x10^-1  =          0.7      

The value of digit 8     =          8x10^-2   =         0.08

The actual number can be found by adding the values obtained by the digits as follows:

100 + 30 + 9 + 0.7 + 0.8          =          139.78

Binary Number System

Digital computer represents all kinds of data and information in the binary system. Binary Number System consists of two digits 0 and 1. Its base is 2. Each digit or bit in binary number system can be 0 or 1. A combination of binary numbers may be used to represent different quantities like 1001. The positional value of each digit in binary number is twice the place value or face value of the digit of its right side. The weight of each position is a power of 2.

The place value of the digits according to position and weight is as follows:

Example: Convert 10111₂ decimal number

 10111₂             =          1 x 2⁴ + 0 x 2³ + 1 x 2² + 1 x 2¹ + 1 x 2⁰

                        =          1 x 16 + 0 + 1 x 4 + 1 x 2 + 1 x 1

                        =          16 + 0 + 4 2 + 1

                        =          23₁₀

Example: Convert 101.101₂

 101.101₂                    =          1 x 2² + 0x2¹ + 1 x 2⁰ + 1x 2^-1 + 0 x 2^-2 + 1 x 2^-3

                                 =          1 x 4 + 0 + 1 x 1 + ½ + 0 + 1/8

                                 =          4 + 0 + 1 + 0.5 + 0.125

                                 =          5.625₁₀

 Octal Number System

Octal Number System consists of eight digits from 0 to 7. The base of octal system is 8. Each digit position in this system represents a power of 8. Any digit in this system is always less than 8. Octal number system is used as a shorthand representation of long binary numbers. The number 641⁸ is not valid in this number system as 8 is not a valid digit.

The place value of each digit according to position and weight is as follows.

Example: convert 45₈ to decimal number

45₈       =          4 x 8¹ + 5 x 8⁰

            =          4 x 8 + 5 x 1

            =          32 + 5

            =          37₁₀     

Hexadecimal number system

The Hexadecimal Number System consists of 16 digits from 0 to 9 and A to F. The alphabets A to F represent decimal numbers from 10 to 15. The base of this number system is 16. Each digit position in hexadecimal system represents a power of 16. The number 764₁₆ is valid hexadecimal number. It is different from 764₁₀ which is seven hundred and sixty four. This number system provides shortcut method to represent long binary numbers.

The place value of each digit according to position and weight is as follows:

Example: Convert 3A₁₆ to decimal number

3A₁₆     =          3 x 16^{1 +} A x 16⁰                                               

            =          3 x 16 + 10 x 1

            =          48 + 10

            =          58₁₀

According to purpose there are two-types of computers.

General-Purpose Computers

Most computers in use today are General-Purpose computers — those built for a great variety of processing jobs. Simply by using a general purpose computer and different software, various tasks can be accomplished, including writing and editing (word processing), manipulating facts in a data base, tracking manufacturing inventory, making scientific calculations, or even controlling organization’s security system, electricity consumption, and building temperature. General purpose computers are designed to perform a wide variety of functions and operations. You will probably use this type of computer reading this article and I am using a general purpose computer typing this article in some software (MS Word). A general purpose computer is able to perform a wide variety of operations because it can store and execute different programs in its internal storage. Unfortunately, having this ability is often achieved at the expense of speed and efficiency. In most situations, however, you will find that having this flexibility makes this compromise a most acceptable one.

                                 Similar Topic: Analog, Digital & Hybrid Computers

Special-Purpose Computers

As the name states, a Special-Purpose Computer are designed to be task specific and most of the times their job is to solve one particular problem. They are also known as dedicated computers, because they are dedicated to perfom a single task over and over again. Such a computer system would be useful in playing graphic intensive Video Games, traffic lights control system, navigational system in an aircraft, weather forecasting, satellite launch / tracking, oil exploration, and in automotive industries, keeping time in a digital watch, or Robot helicopter. While a special purpose computer may have many of the same features found in a general purpose computer, its applicability to a particular problem is a function of its design rather than to a stored program. The instructions that control it are built directly into the computer, which makes for a more efficient and effective operation. They perform only one function and therefore cut down on the amount of memory needed and also the amount of information which can be input into them. As these computers have to perform only one task, therefore, they are fast in processing. A drawback of this specialization, however, is the computer’s lack of versatility. It cannot be used to perform other operations.

Learn about: Super Computers, Mainframe Computers, Mini Computers & Micro Computers

"A printer is an external output device that takes data from a computer and generates output in the form of graphics / text on a paper".

There are two types of printers.

Impact printers

An impact printer makes contact with the paper. It usually forms the print image by pressing an inked ribbon against the paper using a hammer or pins. Following are some examples of impact printers.

 Dot-Matrix Printers

The dot-matrix printer uses print heads containing from 9 to 24 pins. These pins produce patterns of dots on the paper to form the individual characters. The 24 pin dot-matrix printer produces more dots that a 9 pin dot-matrix printer, which results in much better quality and clearer characters. The general rule is: the more pins, the clearer the letters on the paper. The pins strike the ribbon individually as the print mechanism moves across the entire print line in both directions, i-e, from left to right, then right to left, and so on. The user can produce a color output with a dot-matrix printer (the user will change the black ribbon with a ribbon that has color stripes). Dot-matrix printers are inexpensive and typically print at speeds of 100-600 characters per second.

Daisy-wheel printers

In order to get the quality of type found on typewriters, a daisy-wheel impact printer can be used. It is called daisy-wheel printer because the print mechanism looks like a daisy; at the end of each “Petal” is a fully formed character which produces solid-line print. A hammer strikes a “petal” containing a character against the ribbon, and the character prints on the paper. Its speed is slow typically 25-55 characters per second.

Line printers

In business where enormous amount of material are printed, the character-at-a-time printers are too slow; therefore, these users need line-at-a-time printers. Line printers, or line-at-a-time printers, use special mechanism that can print a whole line at once; they can typically print the range of 1,200 to 6,000 lines per minute. Drum, chain, and band printers are line-at-a-time printers.

Drum printer

A drum printer consists of a solid, cylindrical drum that has raised characters in bands on its surface. The number of print positions across the drum equals the number available on the page. This number typically ranges from 80-132 print positions. The drum rotates at a rapid speed. For each possible print position there is a print hammer located behind the paper. These hammers strike the paper, along the ink ribbon, against the proper character on the drum as it passes. One revolution of the drum is required to print each line. This means that all characters on the line are not printed at exactly the same time, but the time required to print the entire line is fast enough to call them line printers. Typical speeds of drum printers are in the range of 300 to 2000 lines per minute.

Chain printers

A chain printer uses a chain of print characters wrapped around two pulleys. Like the drum printer, there is one hammer for each print position. Circuitry inside the printer detects when the correct character appears at the desired print location on the page. The hammer then strikes the page, pressing the paper against a ribbon and the character located at the desired print position. An impression of the character is left on the page. The chain keeps rotating until all the required print positions on the line have filled. Then the page moves up to print the next line. Speeds of chain printers range from 400 to 2500 characters per minute.

Band printers

A band printer operates similar to chain printer except it uses a band instead of a chain and has fewer hammers. Band printer has a steel band divided into five sections of 48 characters each. The hammers on a band printer are mounted on a cartridge that moves across the paper to the appropriate positions. Characters are rotated into place and struck by the hammers. Font styles can easily be changed by replacing a band or chain.

Non-impact printers

Non-impact printers do not use a striking device to produce characters on the paper; and because these printers do not hammer against the paper they are much quieter. Following are some non-impacted printers.

Ink-jet printers

Ink-jet printers work in the same fashion as dot-matrix printers in the form images or characters with little dots. However, the dots are formed by tiny droplets of ink. Ink-jet printers form characters on paper by spraying ink from tiny nozzles through an electrical field that arranges the charged ink particles into characters at the rate of approximately 250 characters per second. The ink is absorbed into the paper and dries instantly. Various colors of ink can also be used.

One or more nozzles in the print head emit a steady stream of ink drops. Droplets of ink are electrically charged after leaving the nozzle. The droplets are then guided to the paper by electrically charged deflecting plates [one plate has positive charge (upper plate) and the other has negative charge (lover plate)]. A nozzle for black ink may be all that’s needed to print text, but full-color printing is also possible with the addition of needed to print text, but full-color printing is also possible with the addition three extra nozzles for the cyan, magenta, and yellow primary colors. If a droplet isn’t needed for the character or image being formed, it is recycled back to its input nozzle.

Several manufacturers produce color ink-jet printer. Some of these printers come with all their color inks in a cartridge; if you want to replace on color, you must replace all the colors. Other color ink-jet printers allow you to replace ink individually. These printers are a better choice if user uses one color more than other colors. These printers produce less noise and print in better quality with greater speed.

Laser printers

A laser printer works like a photocopy machine. Laser printers produce images on paper by directing a laser beam at a mirror which bounces the beam onto a drum. The drum has a special coating on it to which toner (an ink powder) sticks. Using patterns of small dots, a laser beam conveys information from the computer to a positively charged drum to become neutralized. From all those areas of drum which become neutralized, the toner detaches. As the paper rolls by the drum, the toner is transferred to the paper printing the letters or other graphics on the paper. A hot roller bonds the toner to the paper.

Laser printers use buffers that store an entire page at a time. When a whole page is loaded, it will be printed. The speed of laser printers is high and they print quietly without producing much noise. Many home-use laser printers can print eight pages per minute, but faster and print approximately 21,000 lines per minute, or 437 pages per minute if each page contains 48 lines. When high speed laser printers were introduced they were expensive. Developments in the last few years have provided relatively low-cost laser printers for use in small businesses.

Advantages of Laser Printer

• The main advantage of Laser printer is its speed & efficiency at which it prints high-quality quality graphics & text.
• Laser printers produce high-quality output as compared to other printers.
• Laser printers are quite and does not produce disturbing sounds.
• They are also capable to produce color prints.

 Disadvantages of Laser Printer

• The main disadvantage of Laser printer is its cost, they are relatively costly as compared to other printers.
• The maintenance, repair & servicing charges are also high of these printers.
• Laser printers emit small amount of ozone and are hazardous to health and the atmosphere.

What is Input

"Any data or instruction that is used by a computer is called input". This data or instruction can come directly from end user or from other devices. For example, while you prepare word documents or spread sheets, you use the keyboard to enter text & numbers and use command keys to save / print documents. You can also perform operations on computer using voice commands. These are all different methods of providing an input to a computer.

What is Input Device

"Input device translates words, sounds images, and actions that people understand into symbols that the system unit can process".

Input devices include keyboards, Mouse, digital Camera and light pen.

"An input device is a hardware device that is used to provide input (data / instructions) to a computer so that it can be processed".

Besides the widely used input devices like keyboard & Mice there are other different input devices that perform various input operations like a scanner scan images / documents. Webcams capture videos & images.

Keyboard

A keyboard is an essential input device that combines a typewriter keyboard with a numeric keypad. The special purpose keys and the function keys are used to perform a special taks like pressing Control key (CTRL) key in combination with “P” prints a document, or pressing the “F2” function key opens a window with help content about any issue or topic. Nowadays Multimedia keyboards are common as they have task specific keys & buttons. For example, volume control ext. Wireless keyboards are also popular these days, that can be connected to a tablet or a computer via Bluetooth.

Mouse

The mouse is another essential input device that controls the pointer displayed on the monitor. A mouse can have 2 or more buttons. Mostly the Right-Mouse Button and the Left-Mouse button, and a wheel button for scrolling pages.

Mechanical Mouse

A mechanical mouse is considred as the traditional mouse and is now replaced by optical mouse. A mechanical mouse has a ball on the bottom, which is attached to the system unit through a cord. A mechanical mouse requires periodic cleaning.

Optical mouse

Optical Mouse is widely used these days. Like the mechanical mouse, it does not have any moving parts. It emits & senses light to detect mouse movements. Optical mouse can be used on any surface with great precision as compared to Mechanical mouse.

Wireless Mouse

A wireless mouse or cordless mouse uses infrared or radio wares to communicate with the system units. A wireless mouse is battery powered and can be connected to a laptop or tablet computer.

Joystick

A very popular input device that is used for computer games. Different buttons are used for controlling the game. They can be used with gaming consoles like Xbox 360 or Playstation.

Touch Screen

A touch screen is a particular kind of monitor screen covered with a plastic layer. Behind this layer are crisscrossed invisible beams of infrared light. This arrangement enables someone to perform actions by touching the screen with a finger or stylus. With it growing popularity touchscreens are used in smartphones, Automated Teller Machine (ATM) etc.

Optical Scanner

A scanner reads data or information from a source. This source can be a written document, on an image. A scanner, also called optical scanner can copy or reproduce text as well as images.

Bar Code Reader

You must be familiar with a Bar Code Reader from grocery stores & shopping malls. A barcode reader is a photoelectric scanner that reads the bar codes of a product. The bar code reader reads the bar code of a product and displays the information about the product, for example the price of the product.

Since the advent of the first computer different types and sizes of computers are offering different services. Computers can be as big as occupying a large building and as small as a laptop or a microcontroller in mobile & embedded systems.

The four basic types of computers are.

1. Super computer
2. Mainframe Computer
3. Minicomputer
4. Microcomputer

Supercomputer

The most powerful computers in terms of performance and data processing are the supercomputers. These are specialized and task specific computers used by large organizations. These computers are used for research and exploration purposes, like NASA uses supercomputers for launching space shuttles, controlling them and for space exploration purpose.

The supercomputers are very expensive and very large in size. It can be accommodated in large air-conditioned rooms; some super computers can span an entire building.

In 1964, Seymour cray designed the first supercomptuer CDC 6600.

Uses of Supercomputer

In Pakistan and other countries Supercomputers are used by Educational Institutes like NUST (Pakistan) for research purposes. Pakistan Atomic Energy commission & Heavy Industry Taxila uses supercomputers for Research purposes.

Space Exploration

Supercomputers are used to study the origin of the universe, the dark-matters. For these studies scientist use IBM’s powerful supercomputer “Roadrunner” at National Laboratory Los Alamos.

Earthquake studies

Supercomputers are used to study the Earthquakes phenomenon. Besides that supercomputers are used for natural resources exploration, like natural gas, petroleum, coal, etc.

Weather Forecasting

Supercomputers are used for weather forecasting, and to study the nature and extent of Hurricanes, Rainfalls, windstorms, etc.

Nuclear weapons testing

Supercomputers are used to run weapon simulation that can test the Range, accuracy & impact of Nuclear weapons.   

Popular Supercomputers

•  IBM’s Sequoia, in United States
•  Fujitsu’s K Computer in Japan
•  IBM’s Mira in United States
•  IBM’s SuperMUC in Germany
•  NUDT Tianhe-1A in China

Mainframe computer

Although Mainframes are not as powerful as supercomputers, but certainly they are quite expensive nonetheless, and many large firms & government organizations uses Mainframes to run their business operations. The Mainframe computers can be accommodated in large air-conditioned rooms because of its size. Super-computers are the fastest computers with large data storage capacity, Mainframes can also process & store large amount of data. Banks educational institutions & insurance companies use mainframe computers to store data about their customers, students & insurance policy holders.

Popular Mainframe computers

•  Fujitsu’s ICL VME
•  Hitachi’s Z800

Minicomputer

Minicomputers are used by small businesses & firms. Minicomputers are also called as “Midrange Computers”. These are small machines and can be accommodated on a disk with not as processing and data storage capabilities as super-computers & Mainframes. These computers are not designed for a single user. Individual departments of a large company or organizations use Mini-computers for specific purposes. For example, a production department can use Mini-computers for monitoring certain production process.

Popular Minicomputers

•  K-202
•  Texas Instrument TI-990
•  SDS-92
•  IBM Midrange computers

Microcomputer

Desktop computers, laptops, personal digital assistant (PDA), tablets & smartphones are all types of microcomputers. The micro-computers are widely used & the fastest growing computers. These computers are the cheapest among the other three types of computers. The Micro-computers are specially designed for general usage like entertainment, education and work purposes. Well known manufacturers of Micro-computer are Dell, Apple, Samsung, Sony & Toshiba.

Desktop computers, Gaming consoles, Sound & Navigation system of a car, Netbooks, Notebooks, PDA’s, Tablet PC’s, Smartphones, Calculators are all type of Microcomputers.

You might also like reading The Five Generations of Computers

Today, the computer is used in every field and has made our day to day tasks very easy but there are some advantages and disadvantages of computers.

Advantages of Computer

Computer has made a very vital impact on society. It has changed the way of life. The use of computer technology has affected every field of life. People are using computers to perform different tasks quickly and easily. The use of computers makes different task easier. It also saves time and effort and reduces the overall cost to complete a particular task.

Many organizations are using computers for keeping the records of their customers. Banks are using computers for maintaining accounts and managing financial transactions. The banks are also providing the facility of online banking. The customers can check their account balance from using the internet. They can also make financial transaction online. The transactions are handled easily and quickly with computerized systems.

People are using computers for paying their bills, managing their home budgets or simply having some break and watching a movie, listening to songs or playing computer games. Online services like skype or social media websites are used for communication and information sharing purposes.

Computer can be used as a great educational tool. Students can have access to all sort of information on the internet. Some great websites like Wikipedia, Khan’s Academy, Code Academy, Byte-Notes provides free resources for students & professionals.  

Moreover, the computer is being used in every field of life such as medical, business, industry, airline and weather forecasting.

Disadvantages of computer

The use of computer has also created some problems in society which are as follows.

Unemployment

Different tasks are performed automatically by using computers. It reduces the need of people and increases unemployment in society.

Wastage of time and energy

Many people use computers without positive purpose. They play games and chat for a long period of time. It causes wastage of time and energy. Young generation is now spending more time on the social media websites like Facebook, Twitter etc or texting their friends all night through smartphones which is bad for both studies and their health. And it also has adverse effects on the social life.

Data Security

The data stored on a computer can be accessed by unauthorized persons through networks. It has created serious problems for the data security.

Computer Crimes

People use the computer for negative activities. They hack the credit card numbers of the people and misuse them or they can steal important data from big organizations.

Privacy violation

The computers are used to store personal data of the people. The privacy of a person can be violated if the personal and confidential records are not protected properly.

Health risks

The improper and prolonged use of computer can results in injuries or disorders of hands, wrists, elbows, eyes, necks and back. The users can avoid health risks by using the computer in proper position. They must also take regular breaks while using the computer for longer period of time. It is recommended to take a couple of minutes break after 30 minutes of computer usage.

Impact on Environment

The computer manufacturing processes and computer waste are polluting the environment. The wasted parts of computer can release dangerous toxic materials. Green computer is a method to reduce the electricity consumed and environmental waste generated when using a computer. It includes recycling and regulating manufacturing processes. The used computers must be donated or disposed off properly.

Cathode Ray Tube (CRT)

This monitor uses a Cathode Ray Tube (CRT). CRT tube creates an image on the screen using a beam of electrons. CRT consists of one or more guns that fire a beam of electrons inside the screen. The screen is coated with very tiny Phosphor dots from inside. The beam of electrons repeatedly falls on the surface of screen. Every beam fall takes only a fraction of second. CRT in color monitors consists of three guns. These guns generate red, green and blue (RGB) colors. The other colors are generated with a combination of these three colors. Nowadays, most of the CRT monitors are replaced by Flat Panel Monitors.

Flat Panel Monitors

Flat Panel Monitors take less space and are lightweight. These monitors use much less power than CRTs. It does not emit harmful radiations. It is much expensive than CRT. Notebook computers, PDA and cellular phones use flat panel monitors. Flat panel monitors are available in different sizes such as 15”, 17”, 18” & 19” etc.

Flat panel display is made up of two plates of glass. These plates contain a substance between them. The substance is activated in different ways.

There are two types of technologies used in flat panel display screens.

Liquid Crystal Display

Liquid crystal display screen contains a substance called liquid crystal. The molecules of this substance line up in such a way that the light behind the screens blocked or allowed to create an image. LCDs provide a sharper picture than CRTs and emit less radiation. LCD displays requires less power and take up less space than CRT.

Gas plasma Display

Gas plasma display uses gas plasma technology. This technology uses a layer of gas between two glass plates. The gas release ultraviolet light when voltage is applied. The pixels on the screen glow due to this ultraviolet light and form an image. Plasma display is available in the sizes of upto 150 inches wide. It provides richer colors than LCD monitors but are more expensive. That is why, it is not commonly used. It provides higher display quality. This type of monitor can hand directly on a wall.

Touch Screen Monitors

Touch screen monitors are used for input as well as output. A touch screen is a special type of visual display unit. It has a grid of light beams or fine wires on the screen. It lets the user to interact with a computer by the touch of a finger rather than typing on a keyboard or moving a mouse. The user enters data by touching icons or menus identified on the screen.

Most touch screen computers use sensors to detect touch of a finger. Touch screen is well suited for simple applications like ATM. It has also become common in department stores and supermarkets.

Types of touch Screen Monitors

There are different types of touch screen technology. The most common types are Resistive, Surface wave & Capacitive.

Resistive Touch Screen

This monitor usually has a coat of thin electrically conductive and resistive layer of metal. A change in electrical current occurs when it is pressed. The input can be processed by a computer. These monitors are the most popular types of touch screen monitors used today. They are usually not affected by dust or liquids which make them very reliable.

Surface Wave Touch Screens

These monitors use ultrasonic waves to process input from the screen. These waves flow over the touch screen. The wave is absorbed and processed by computer when a person touches the pad.

Capacitive Touch Screen

These screens are coated with indium tin oxide. This material provides continuous current across the screen. The current can be measure by the processor when the pad is touched. It is usually used with a bare finger instead of stylus. These screens have high clarity and are not affected by dust. Nowadays most of the smartphones have Capacitive Touch screens.

Embedded computers (Embedded Systems) are Task-Specific which means they are optimized to perform a specific task. It works as a component in a larger product. These computers are very small in size and have limited hardware.

Computers are used in so many fields in daily life. From Engineers to Doctors, Students, Teachers, Government Organization they all use computers to perform specific tasks, for entertainment or just to finish office work.

Computers have become part of our life. We use computers on daily basis, in our school, at home, at office. Why we are so dependent on computers? Because they have made our lives easier, they provide us entertainment, they can store our valuable data for as long as we want it to keep. The following are some of the characteristics of a computers.

Computer is derived from a Latin word “computare” which means to “to calculate”, “to count”, “to sum up” or “to think together”. So, more precisely the word computer means a "device that performs computation".

Computer Virus is a malicious software program “Malware” that can infect a computer by modifying or deleting data files, boot sector of a hard disk drive or cases a software program to work in an unexpected manner.

Another term called “Internet crime” refers to criminal activities for exploiting the internet. These crimes include and is not limited to identity theft, threatening a nation’s security, copyright infringement and child pornography. These crimes have become a threat to individual privacy, where confidential data, individual’s identity or photos and videos etc. is stolen or intercepted by the attacker.

Many people take the internet and the Web as the same thing, but they are not the same. The Internet is the actual physical network which comprises of wires, cables & Satellites. They connect computers across the globe. The Web on the other hand is a multimedia interface to resources and information that we find over the internet.

Computer is very expensive hardware and it contains vital information and your personal data. It is very important to take good care of your computer to avoid any mishaps. Following steps are essential for Computer Security and to protect your computer and the data against any threats.