My Profile
Active Members
TodayLast 7 Days
more...
Awards & Gifts
Online Exams
Fresher Jobs
Our fresher job section is exclusively for fresh graduates! Find jobs for freshers in major Indian
cities including Bangalore, Chennai, Hyderabad, Pune or Kochi
Resources
Find educational articles, blogs, discussion threads and other resources.
Colleges
Find details about any college in India or search for courses.
|
Introduction to computers:-
Posted Date: 06 Feb 2008 Resource Type: Articles/Knowledge Sharing Category: Computer & Technology
|
Posted By: prakash Member Level: Silver
Rating:  Points: 5
|
|
|
Introduction to computers
INTRODUCTION
A computer is a programmable machine. The two principal characteristics of a computer are:
• It responds to a specific set of instructions in a well-defined manner.
• It can execute a prerecorded list of instructions.
All general-purpose computers require the following hardware components:
• Central processing unit (CPU)
• Memory
• Input devices
• Output devices
• Mass storage device
TYPES OF COMPUTERS
Computers can be classified by their size and power as follows:
Personal computer: A small, single-user computer based on a microprocessor.
Workstation: A powerful, single - user computer, but has a more powerful microprocessor and a high –quality monitor.
Minicomputer: A multi-user computer capable of supporting 10 to 100 of users simultaneously.
Mainframe: A powerful multi-user computer capable of supporting many hundreds of users simultaneously.
Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second.
CHARACTERISTICS OF COMPUTERS
All computers have certain common characteristics irrespective of their type and size. Following are the characteristics of computers.
Word length
A digital computer operates on binary digits 0 and 1. A binary digit is called a bit. A group of 8 bits is called a byte. The number of bits that a computer can process at a time in parallel is called its word length. Commonly used are 8,16,32,64 bits.
Speed
Computers can calculate at very high speeds. A microcomputer for example, can execute millions of instructions per second over and over again. As the power of the computer increases, the speed also increases.
Storage
Computers have their main memory and auxiliary memory systems. A computer can store a large amount of data. With more and more auxiliary storage devices, which are capable of storing huge amounts of data, the storage capacity of a computer is virtually unlimited.
Accuracy
The accuracy of a computer system is very high. Errors in hardware can occur, but error detecting and correcting techniques will prevent false results. In most cases, the errors are due to the human factor rather than the technological flaws.
Versatility
Computers are very versatile machines. They can perform activities ranging from simple calculations to performing complex CAD modeling and simulation to navigating missiles and satellites.
Automation
The level of automation achieved in a computer is phenomenal. They will execute the programs in the correct sequence, they will switch on/off the machines at the appropriate time, they will monitor the operational parameters, they will send warning signals or take corrective actions if the parameters exceed the control level, and so on.
Diligence
Diligence means being constant and earnest in effort and application. After sometime people will become bored and tedium will set in. This will affect the performance. Being a machine, a computer does not have any of these human weaknesses. They will perform the tasks that are given to them, irrespective of whether it is interesting, creative, monotonous or boring.
Five generations of modern computers
FIRST GENERATION (1945-1956)
In 1946 two engineers at the University of Pennsylvania, John Presper Eckert (1919-1995) and John W.Mauchly (1907-1980) built the first digital computer using parts called vacuum tubes. They named their new invention as ENIAC. In the mid-1940’s John Von Neumann initiating concepts in computer design that remained central to computer engineering for the next 40 years. Von designed the Electronic Discrete Variable Automatic Computer (EDVAC) in 1947 with a memory to hold both a stored program as well as data. The key element to Von is the central processing unit, which allowed all computer functions to get coordinated through a single source. In 1951, UNIVAC1 (Universal Automatic Computer) built by Remington Rand, became one of the first commercially available computers to take advantage of these advances. Other distinctive features of first generation computers were the use of vacuum tubes and magnetic drums for data storage.
SECOND GENERATION (1956-1963)
In 1948, the invention of the transistor greatly changed the computer’s development. The transistor replaced the large, cumbersome vacuum tube in televisions, radios and computers. Second generation computers replaced machine language with assembly language, allowing abbreviated programming codes to replace long, difficult binary codes. They also contained all the components we associate with the modern day computer: printers, tape storage, disk storage, memory, operating systems and stored programs. One example was IBM 1401, which was universally accepted throughout the industry, and is considered by many to be the Model T of the computer industry. The stored program concept meant that instructions to run a computer for a specific function were held inside the computer’s memory, and could quickly be replaced by a different set of instructions for a different function. More sophisticated high-level languages such as COBOL, FORTRAN came into common use during the time and has expanded to the current day.
THIRD GENERATION (1964-1971)
Though transistors were clearly an improvement over the vacuum tube, they still generated a great deal of heat, which damaged the computer’s sensitive internal parts.
Jack Kilby, an engineer with Texas instruments developed the integrated circuit in 1958. The IC combined three electronic components onto a small silicon disc, which was made from quartz. Scientists later managed to fit even more components on a single chip, called a semiconductor. As a result computers became ever smaller as more components were squeezed onto the chip. The situation changed in 1964 when IBM announced a third generation of computing hardware its System/360 family of mainframe computers. Each processor in this family had a large set of built-in instructions that it could execute.
FOURTH GENERATION (1971-PRESENT)
Large-scale integration (LSI) could fit hundreds of components onto one chip. By the 1980’s very large scale integration (VLSI) squeezed hundreds of components onto a chip. Ultra-large scale integration (ULSI) increased that number into the millions. In 1981 IBM introduced its personal computer for use in the homes, offices and schools. As opposed to mainframe computers, which was one powerful computer that shared time with many terminals for many applications, networked computers allowed individual computers to form electronic co-ops. Using either local area network or telephone lines these networks could reach enormous proportions. A global web of computer circuitry the Internet, for example, links computers worldwide into a single network of information.
FIFTH GENERATION (PRESENT AND BEYOND)
The most famous example of a fifth generation computer is the fictional HAL9000 from Arthur C.Clarks. Hal performed all of the functions currently envisioned for real-life fifth generation computers. With artificial intelligence HAL could reason well enough to hold conversations with its human operators, use visual input, and learn from its own experiences. The ability to translate a foreign language is also a major goal of fifth generation computers.
Another advance is superconductor technology, which allows the flow of electricity with little or no resistance, greatly improving the speed of information flow. Computers today have some attributes of fifth generation computers. Fifth generation computers aim to be able to solve highly complex problems, ones, which require reasoning, intelligence and expertise when solved by people. As said before they are being designed to contain a large number of processors, grouped into three major subsystems: a knowledge base system, an inference mechanism and an intelligent user interface. There are five major programs under way to develop fifth generation computers:
• The ICOT program in Japan.
• The MCC project in the USA.
• The DARPA project in the USA.
• The Esprit initiative in the EC.
• The Alvey program in Britain.
Classification of digital computer systems
Computer systems are classified as Microcomputers, Minicomputers, Mainframes and Supercomputers.
MICROCOMPUTERS
The most familiar kind of computer is the microcomputer. Microcomputers have been considered to be of two types Personal computers and Workstations.
Personal computers
Recently PCs were desktop or portable machines. These machines ran comparatively easy-to-use applications software such as the word processors, spreadsheets, etc. most important they did not have the processing power that workstations did. Examples of personal computers are Acer’s Aspire, Compaq Presario, etc.
Workstations
Workstations are, again, until recently, expensive, powerful machines used by engineers, scientists, and other professionals who processed a lot of data. People who need to run complex programs and display both work in progress and results graphically also use workstations. Examples are workstations made by Sun, Apollo, Hewlett-Packard, NeXT and IBM.
Portable computers
One type of PC that is rapidly growing in popularity is the portable computer, which can be easily carried around. There are three categories of portable computers:
Laptops or Notebook PCs, Subnotebooks and Personal Digital Assistants.
Laptops or Notebooks: Laptops may be either AC-powered, battery-powered, or both. These computers are ideal for users who have to work away from their offices. An example is IBM ThinkPad.
Subnotebooks: Subnotebooks are for frequent flyers and life-on-the-road professionals. Sub notebook users give up a full display screen and keyboard in exchange for less weight. An example is Toshiba Protégé.
Personal Digital Assistants (PDAs): PDAs are much smaller than the subnotebooks. They combine pen input, writing recognition, personal organization tools, and communication capabilities in a very small package.
MINICOMPUTERS
Minicomputers also known as mid range computers were first developed as special-purpose mainframe computers. They were used, for instance, to control machines in a manufacturing unit. One of the popular minicomputer systems is the VAX made by Digital Equipment Corp. Minicomputers work well in what are known as Distributed Data Processing (DDP).
MAINFRAMES
Mainframe computers can process several million-program instructions per second. Large organizations rely on these room-size systems to handle large programs with lots of data. Mainframes are mainly used by insurance companies, banks, airline and railway reservation systems, etc. An advanced mainframe made by IBM is S/390.
SUPERCOMPUTERS
Supercomputers are the fastest calculating devices ever invented. A desktop microcomputer processes data and instructions in millionths of a second, or microseconds. A supercomputer, by contrast, can operate at speeds measured in nanoseconds and even in Pico seconds – one thousand to one million times as fast as microcomputers. Examples are weather forecasting, oil exploration, weapons research, and large-scale simulation. These supercomputers consist of thousands of integrated microprocessors.
NETWORK COMPUTERS
Network computers are computers with minimal memory, disk storage and processor power designed to connect to a network, especially the Internet. The idea behind network computers is that many users who are connected to a network don’t need all the computer power they get from a typical personal computer. Instead they can rely on the power of the network servers. Oracle Corporation and Sun Microsystems are leading the crusade for network computers and have even created a Network computer reference profile.
Anatomy of a Digital Computer
FUNCTIONS AND COMPONENTS OF A COMPUTER
The computer needs both hardware and software. Hardware consists of the mechanical and electronic devices, which we can see and touch. The software consists of programs, the operating systems and the data that reside in the memory and storage devices. A computer does mainly the following four functions:
• Receive Input
• Process Information
• Produce Output
• Store Information
Computer hardware falls into two categories: processing hardware, which consists of the central processing unit (CPU). The CPU as its name implies is where the data processing is done. Peripheral devices allow people to interact with the CPU.
CENTRAL PROCESSING UNIT (CPU)
The part of the computer that executes program instructions is known as the processor or central processing unit (CPU). The CPU has two parts: the control unit and the arithmetic logic unit (ALU). In a microcomputer both are on the microprocessor chip.
Control unit
The control unit tells the rest of the computer system how to carry out a program’s instructions. It directs the movement of electronic signals between memory - which temporarily holds data, instructions and processes information and the ALU. It also directs these control signals between the CPU and input / output devices.
Arithmetic – Logic Unit (ALU)
Arithmetic – Logic Unit, usually called the ALU, performs two types of operations – arithmetic and logical. Arithmetic operations are the fundamental mathematical operations consisting of addition, subtraction, multiplication and division. Logical operations consist of comparisons.
Memory
Memory also known as the primary storage or main memory - is a part of the microcomputer that holds data for processing, instructions for processing the data (the program) and information (processed data).
Registers
Computers also have several additional storage locations called registers. These appear in the control unit and ALU and make processing more efficient. Registers are a sort of special hi-speed staging areas that hold data and instructions temporarily during processing. They are parts of the control unit and ALU rather than the memory.
Addresses
To locate the characters of data or instructions in the main memory, the computer stores them in locations known as addresses. A unique number designates each address. Addresses can be compared to post office mailboxes. Their numbers stay the same, but contents continuously change.
How the CPU and Memory work
The various steps involved for multiplying two numbers is shown below:
1. The control unit recognizes that the program has been loaded into memory. It begins to execute the first step in the program
2. The program tells the user, “Enter 1st number”.
3. The user types the number 10 on the keyboard. An electronic signal is sent to the CPU.
4. The control unit recognizes this signal and routes the signal to an address in memory – address 7.
5. After completing the above instruction, the next instruction tells user, “ Enter 2nd number”.
6. The user types the number 4 on the keyboard. An electronic signal is sent on the CPU.
7. The control unit recognizes this signal and routes it to memory address 8.
8. The next program instruction is executed – “Multiply 1st and 2nd numbers”.
9. To execute this instruction, the control unit informs the ALU that two numbers are coming and the ALU is to multiply them. The control unit next sends to the ALU a copy of the contents of address 7(10) and address 8(4).
10. ALU performs the multiplication: 10 * 4 = 40.
11. The control Unit sends a copy of the multiplied result (40) back to memory, to address 9.
12. The next program instruction is executed: “Print the Result”.
13. To execute this instruction, the control unit sends the contents of the address 9(4)) to the monitor.
14. Monitor displays the value 40.
15. Final instruction is executed: “end”. The program is complete.
So the actual working of the CPU and memory is much more complicated.
Memory Units
INTRODUCTION
Memory units are the internal storage areas in a computer. The term “memory” identifies the data storage that comes in the form of chips, and the word “storage” is used for memory that exists on tapes or disks. There are several different types of memory. They are:
? RAM (Random–Access Memory)
? ROM (Read-Only Memory)
? PROM (Programmable Read-Only Memory)
? EPROM (Erasable Programmable Read-Only Memory)
? EEPROM (Electrically Erasable Programmable Read-Only Memory)
RAM
A type of computer memory that can be accessed randomly; that is, any byte of memory can be accessed without touching the preceding bytes. RAM is the most common type of memory found in computers and other devices, such as printers. There are two basic types of RAM:
? Dynamic RAM (DRAM)
? Static RAM (SRAM)
Dynamic RAM needs to be refreshed thousands of times per second. Static RAM needs to be refreshed less often, which makes it faster; but it is also more expensive than dynamic RAM. Both types of RAM are volatile, meaning that they lose their contents when the power is turned off. In common usage, the term RAM is synonymous with main memory, the memory available to programs.
ROM
Pronounced ROM, acronym for read-only memory, a computer memory on which data has been prerecorded. Once data has been written onto a ROM chip, it cannot be removed and can only be read. Unlike the main memory (RAM), ROM retains its contents even when the computer is turned off. ROM is referred to as being nonvolatile, whereas RAM is volatile. Most personal computers contain a small amount of ROM that stores critical programs such as the program that boots the computer. In addition, ROMs are used extensively in calculators and peripheral devices such as laser printers, whose fonts are often stored in ROMs.
PROM
A PROM is a memory chip on which data can be written only once. Once a program has been written onto a PROM, it remains there forever. Unlike the main memory, PROMs retain their contents when the computer is turned off. The difference between a PROM and a ROM is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process.
EPROM
EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROMs are used to widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery.
EEPROM
EEPROM retains its contents even when the power is turned off. EEPROM is similar to flash memory. The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks.
FLASH MEMORY
Flash memory is a special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS (Basic Input Output System) stored on a flash memory chip so that it can easily be updated if necessary. Such BIOS is sometimes called flash BIOS.
Input Devices
An input device is any machine that feeds data into a computer. For example, a keyboard is an input device, whereas a display monitor is an output device. Other alternate input devices are: Mice, trackballs, and light pens.
KEYBOARD
Keyboard is an input device consisting of a set of type writer-like keys that enable you to enter data into a computer. The standard layout of letters, numbers and punctuation is known as a QWERTY keyboard because the first six keys on the top row of letters spell QWERTY.
There is no standard computer keyboard, although many manufacturers imitate the keyboards of PCs. There are actually three different PC keyboards:
• The Original PC keyboard with 84 keys
• The AT keyboard with 84 keys
• The Enhanced keyboard with 101 keys
With these basic key sets IBM and Apple Macintosh are having additional special-function keys.
MOUSE
Mouse is a device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object you can roll along a hard, flat surface. As you move the mouse, the pointer on the display screen moves in the same direction. Mice contain at least one button and sometimes as many as three, which have different functions depending on what program is running. Mouse is invented by Douglas Engel Bart of Stanford Research Center in 1963, and pioneered by Xerox in the 1970s. In particular, the mouse is important for graphical user interfaces because you can simply point to options and objects and click a mouse button.
Types of Mice
There are three basic types of mice. They are Mechanical, Optomechanical, and Optical.
Mechanical: Has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
Optomechanical: Same as a mechanical mouse, but uses optical sensors to detect motion of the ball.
Optical: Uses a laser to detect the mouse’s movement. You must move the mouse along a special mat with a grid so that the optical mechanism has a frame of reference. Optical mice have no mechanical moving parts. They respond more quickly and precisely than mechanical and optomechanical mice, but they are also more expensive.
Connections
Mice connect to PCs in one of three ways:
Serial mice connect directly to an RS-232C serial port or a PS/2 port. This is the simplest type of connection.
Bus mice connect to the bus through an interface card. This is somewhat more complicated because you need to configure and install an expansion board.
Cordless mice aren’t physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer.
Mouse pad
Mouse pad is a pad over which you can move a mouse. Mouse pads provide more traction than smooth surfaces such as glass and wood, so they make it easier to move a mouse accurately. For mechanical mice, mouse pads are optional. Optical mice, however, require special mouse pads that have grids drawn on them.
TRACKBALL
Trackball is another pointing device. Essentially, a trackball is a mouse lying on its back. To move the pointer, you rotate the ball with your thumb, your fingers, or the palm of your hand. There are usually one to three buttons next to the ball, which you use just like mouse buttons. The advantage of trackballs over mice is that the trackball is stationary so it does not require much space to use it.
JOYSTICK
A joystick is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse. With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, you must return the joystick to its upright position. Most joysticks include two buttons called triggers.
DIGITIZING TABLET
This is an input device that enables you to enter drawings and sketches into a computer. A digitizing tablet consists of an electronic tablet and a cursor or pen. A cursor or a puck is similar to a mouse, except that it has a window with cross hairs for pinpoint placement, and it can have as many as 16 buttons. A pen or a stylus, which looks like a simple ballpoint pen but uses an electronic head instead of ink. The static nature of digitizing tablets makes them particularly effective for tracking drawings.
SCANNERS
Scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. A scanner works by digitizing an image – dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. To edit text read by an optical scanner, you need an optical character recognition (OCR) system to translate the image into ASCII characters. Scanners differ from one another in the following respects: scanning technology, resolution, bit depth, size and shape.
DIGITAL CAMERA
Images can be input into a computer using a digital camera. These images can then be manipulated in many ways using the various imaging tools available. The digital camera takes a still photograph, stores it, and then sends it as digital input into the computer. The images are than stored as digital files.
MICR
Magnetic Ink Character Recognition (MICR) allows the computer to recognize characters printed using magnetic ink. MICR is a direct-entry method used in banks. This technology is used to automatically read those frustrating-looking numbers on the bottom of the cheque. A special-purpose machine known as a reader/sorter reads characters made of ink containing magnetized particles.
OCR
Optical Character Recognition (OCR) refers to the branch of computer science that involves reading text from paper and translating the images into a form that the computer can manipulate. An OCR system enables you to take a book or a magazine article and feed it directly into an electronic computer file. All OCR systems include an optical scanner for reading text, and sophisticated software for analyzing images. Most OCR systems use a combination of hardware and software to recognize characters, although some inexpensive systems do it entirely through software. Advanced OCR systems can read text in a large variety of fonts, but they still have difficulty with handwritten text.
OMR
Optical Mark Recognition (OMR) also called mark sensing is a technology where an OMR device senses the presence or absence of a mark, such as a pencil mark. OMR is used in tests such as aptitude tests.
BAR CODE READER
Bar code readers are photoelectric scanners that read the bar codes, or vertical zebra striped marks, printed on product containers. Supermarkets use a bar code system called the Universal Product Code (UPC). The bar code identifies the product to the supermarket’s computer, which has a description and the latest price of the product. The computer automatically tells the POS (Point of Sales) terminal what the price is.
SPEECH INPUT DEVICES
Speech or voice input devices convert a person’s speech into digital form. These inputs devices, when combined with appropriate software, from voice recognition systems. These systems enable users to operate microcomputers using voice commands. Some of these systems must be ‘trained’ to the particular user’s voice. There are even systems that will translate from one language to another, such as from English to Japanese. There are two types of voice recognition systems: continuous speech and discrete word.
Continuous Speech
Continuous speech recognition systems are used to control a microcomputer’s operations and to issue commands to special application programs. For example, rather than using the keyword to save a spreadsheets file, the user could simply say “ save the file”. Two popular systems are Apple Computer’s Plain Talk and IBM’s continuous speech series.
Discrete-Word
A common activity in business is preparing memos and other written documents. Discrete-Word recognition systems allow users to dictate directly into a microcomputer using a microphone. IBM Voice Type Simply Speaking is an example.
TOUCH SCREEN
Touch screen is a type of display screen that has a touch-sensitive transparent panel covering the screen. Instead of using a pointing device such as a mouse or light pen, you can use your finger to point directly to objects on the screen. In addition, most users find touch-screens tiring to the arms after long use.
TOUCH PAD
A small, touch-sensitive pad used as a pointing device on some portable computers. By moving a finger or other object along the pad, you can move the pointer on the display screen.
LIGHT PEN
Light pen is an input device that utilizes a light-sensitive detector to select objects on a display screen. A light pen is similar to a mouse, except that with a light pen you can move the pointer and select objects on the display screen by directly pointing to the objects with the pen.
Output Devices
INTRODUCTION
An output device is any machine capable of representing information from a computer. Output devices include display screens, loudspeakers, printers, plotters, etc.
MONITOR
Monitor is another term for the display screen. The term monitor, however, usually refers to the entire box, whereas display screen can mean just the screen.
CLASSIFICATION OF MONITORS – BASED ON COLOR
There are many ways to classify monitors. The most basic is in terms of color capabilities, which separates monitors into three classes:
Monochrome
Monochrome monitors actually display two colors, one for the background and one for the foreground. The colors can be black and white, green and black, or amber and black.
Gray-scale
A gray-scale monitor is a special type of monochrome monitor capable of displaying different shades of gray.
Colour
Colour monitors can display anywhere from 16 to over 1 million different colours. Colour monitors are sometimes called RGB monitors because they accept three separate signals – red, green and blue. An RGB monitor consists of a vacuum tube with three electron guns – one each for red, green and blue at one end and the screen at the other end. The number of bits they use to represent each pixel often classifies colour and gray-scaling monitors. For example, an 8-bit monitor represents each pixel with 8 bits. The more bits per pixel, the more colours and shades of gray the monitor can display.
CLASSIFICATION OF MONITORS - BASED ON SIGNALS
Another common way of classifying monitors is in terms of the type of signal they accept: analog or digital.
Digital monitor
A digital monitor accepts digital signals rather than analog signals. A digital monitor then translates the digital signals into analog signals that control the actual display. Although digital monitors are fast and produce clear images, they cannot display variable colours continuously. Consequently, only low-quality video standards, such as MDA, CGA, and EGA specify digital signals.
Analog monitor
This is the traditional type of colour display screen that has been used for years in televisions. In reality, all monitors based on CRT technology are analog. Some monitors have fixed frequency, which means that they accept input at only one frequency. Another type of monitor, called a multiscanning monitor, automatically adjusts to the frequency of the signals being sent to it. This means that it can accept input from different types of video adapters. Like fixed-frequency monitors, multicasting monitors accept TTL, analog, or both types of input.
CHARACTERISTICS OF A MONITOR
Size
The most important aspect of a monitor is its screen size. Like televisions, screen sizes are measured in diagonal inches, the distance from one corner to the opposite corner diagonally. A typical size for small VGA monitors is 14 inches. Monitors that are 16 or more inches diagonally are often called full-page monitors.
Resolution
The resolution of a monitor indicates how densely the pixels are packed. Pixel is short for Picture Element. A pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands of pixels, arranged in rows and columns. The pixels are so close together that they appear connected.
Bandwidth
The amount of data that can be transmitted in a fixed amount of time is known as bandwidth. For digital devices, the bandwidth is usually expressed in bits or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).
Refresh rate
Display monitors must be refreshed many times per second. The refresh rate determines how many times per second the screen is to be refreshed.
Interlaced or Non-interlaced
Interlacing is a display technique that enables a monitor to provide more resolution inexpensively. With interlacing monitors, the electron guns draw only half the horizontal lines with each pass. Because the interlacing monitor refreshes only half the lines at one time, it can display twice as many lines per refresh cycle, giving it greater resolution.
Dot-Pitch
Dot-pitch is a measurement that indicates the vertical distance between each pixel on a display screen. Measured in millimeters, the dot pitch is one of the principal characteristics that determine the quality of display monitors.
Convergence
Convergence refers to how sharply an individual colour pixel on a monitor appears. Each pixel is composed of three dots – a red, blue, and green one. If the dots are badly misconverged, the pixel will appear blurry. All monitors have some convergence errors, but they differ in degree.
VIDEO STANDARDS
There are a variety of video standards that define resolution and colours for displays. Support for a graphics standard is determined by both the monitor and the video adapter. The monitor must be able to show the resolution and colours defined by the standard, and the video adapter must be capable of transmitting the appropriate signals to the monitor. Listed here, in approximate order of increasing power and sophistication, are the more popular video standards for PCs.
Standard Resolution Simultaneous Colours
VGA 640*480
320*200 16
256
SVGA 800*600
1024*768
1280*1024
1600*1200 16
256
256
256
XGA 640*480
1024*768 65536
256
TI 34010 1024*768 256
Popular video standards for PCs
VGA
VGA stands for Video Graphics Array, a graphics display system for PCs developed by IBM. VGA has become one of the de facto standards for PCs. In text mode, VGA systems provide a resolution of 720 by 400 pixels. In graphics mode, the resolution is either 640 by 480 or 320 by 200. The total palette of colours is 262,144.
SVGA
Short for Super VGA, a set of graphics standards designed to offer greater resolution than VGA. There are several varieties of SVGA, each providing a different resolution:
• 800 by 600 pixels
• 1024 by 768 pixels
• 1280 by 1024 pixels
• 1600 by 1200 pixels
All SVGA standards support a palette of 16 million colours, but the number of colours that can be displayed simultaneously is limited by the amount of video memory installed in a system.
XGA
Short for eXtended Graphics Array, a high-resolution graphics standard introduced by IBM in 1990. XGA was designed to replace the older 8514/A video standard. It provides the same resolutions, but supports more simultaneous colours. In addition, XGA allows monitors to be non-interlaced.
TI 34010
TI 34010 is a video standard from Texas Instruments that supports a resolution of 1024 by 768. TI34010 conforms to TI’s Graphics Architecture (TIGA).
PRINTER
Printer is a device that prints text or illustrations on paper and in many cases on transparencies and other media. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories.
Daisy-Wheel Printer
Daisy-Wheel printers are a type of printer that produces letter-quality type. A daisy-wheel printer works on the same principle as a ball-head typewriter. The daisy wheel is a disk made of plastic or metal on which characters stand out in relief along the outer edge. Daisy-wheel printers cannot print graphics, and in general they are noisy and slow, printing from 10 to about 75 characters per second.
Dot-Matrix Printer
Dot-Matrix printers create characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations. Dot-Matrix printers vary in two different characteristics: Speed and Print Quality. Dot-Matrix printers are inexpensive and relatively fast, but they do not produce high-quality output.
Ink-Jet Printers
Ink-Jet printer’s work by spraying ionized ink at a sheet of paper. Magnetized plates in the ink’s path direct the ink onto the paper in the desired shapes. Ink-jet printers are capable of producing high quality print approaching that produced by laser printers. A typical ink-jet printer provides a resolution of 300 dots per inch, although some newer models offer higher resolutions.
Laser Printer
Laser printer utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits. The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure.
One of the chief characteristics of laser printers is their resolution- how many dots per inch they lay down. In addition to the standard monochrome laser printer, which uses a single toner, there also exist colour laser printers that use four toners to print in full colour. Laser printers produce very high-quality print and are capable of printing an almost unlimited variety of fonts. In addition to text, laser printers are very adept at printing graphics.
LCD & LED Printers
Similar to a laser printer but uses liquid crystals or light-emitting diodes rather than a laser to produce an image on the drum.
Line Printer
Line printers are high-speed printers capable of printing an entire line at one time. A fast line printer can print as many as 3,000 lines per minute. The disadvantages of line printers are that they can print only one font, they cannot print graphics, the print quality is low, and they are very noisy.
Thermal Printer
Thermal printers are printers that produce images by pushing electrically heated pins against special heat-sensitive paper. Thermal printers are inexpensive and are used in most calculators and many fax machines. They produce low-quality print, and the paper tends to curl and fade after a few weeks or months.
PLOTTER
Plotter is a device that draws pictures on paper based on commands from a computer. Plotters differ from printers in that they draw lines using a pen. As a result, they can produce continuous lines, whereas printers can only simulate lines by printing a closely spaced series of dots. In general, plotters are considerably more expensive than printers. They are used in engineering applications where precision is mandatory.
SOUND CARDS & SPEAKERS
Sound cards are necessary for nearly all CD-ROMs and have become commonplace on modern personal computers. Sound cards enable the computer to output sound through speakers connected to the board, to record sound input from a microphone connected to the computer, and manipulate sound stored on a disk. Nearly all sound cards support MIDI, a standard for representing music electronically. Sound cards use two basic methods to translate digital data into analog sounds.
FM (Frequency Modulation) Synthesis mimics different musical instruments according to built-in formulas.
Wavetable Synthesis relies on recordings of actual instruments to produce sound. Wavetable synthesis produces more accurate sound, but is more expensive.
Auxiliary storage Devices
INTRODUCTION
Auxiliary storage also known as auxiliary memory or secondary storage, is the memory that supplements the main storage. This is a long-term, non-volatile memory. The term non-volatile means it stores and retains the programs and data even after the computer is switched off. The most common types of auxiliary storage devices are magnetic tapes, magnetic disks, floppy disks, hard disks, etc. There are two types of auxiliary storage devices. This classification is based on the type of data access:
• Sequential
• Random
Sequential access: In the case of sequential-access media, the data stored in the media can only be read in sequence and to get to a particular point on the media you have to go through all the preceding points. Examples are magnetic tapes.
Random access: In contrast, disks are random-access also called direct-access media because a disk drive can access any point at random without passing through intervening points. Examples are magnetic disks, optical disks, zip disks.
MAGNETIC TAPE
Magnetic tape is a magnetically coated strip of plastic on which data can be encoded. Tapes for computers are similar to the tapes used to store music. Tapes also have large storage capacities, ranging from a few hundred kilobytes to several gigabytes. Accessing data on tapes, however, is much slower than accessing data on disks. Because tapes are so slow, they are generally used only for long-term storage and backup. Data to be used regularly is almost always kept on a disk. Tapes come in a variety of sizes and formats. They are shown below:
Type Capacity
Half-inch 60MB-400MB
Quarter-inch 40MB-5GB
8-mm Helical-scan 1GB-5GB
4-mm DAT 2GB-24GB
Types of tapes
Tapes are sometimes called streamers or streaming tapes.
HARD DISK
Hard disk is a magnetic disk on which you can store computer data. The term hard is used to distinguish it from a soft, or floppy, disk. Hard disks hold more data and are faster than floppy disks. A hard disk, for example, can store anywhere from 10 megabytes to several gigabytes, whereas most floppies have a maximum storage capacity of 1.4 megabytes.
A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each plotter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84 megabyte hard disk for a PC might have two platters and 1053 cylinders. There are two types of removable hard disks: disk packs and removable cartridges.
FLOPPY DISK
Floppy disk is a soft magnetic disk. It is called floppy because it flops if you wave it. Unlike most hard disks, floppy disks are portable, because you can remove them from a disk drive. Disk drives for floppy disks are called floppy drives. Floppy disks are slower to access than hard disks and have less storage capacity, but they are less expensive and are portable. Floppies come in two basic sizes:
51/4 inch:
The common size for PCs made before 1987. This type of floppy is generally capable of storing between 100K and 1.2MB of data. The most common sizes are 360K and 1.2MB.
31/2 inch:
Floppy is something of a misnomer for these disks, as they are encased in a rigid envelope. Despite their small size, microfloppies have a larger storage capacity than their cousins – from 400K to 1.4MB of data. The most common sizes for PCs are 720K and 1.44MB. Macintoshes support disks of 400K, 800K, and 1.2MB.
CD-ROM
Abbreviation for CD-ROM is Compact Disc-Read-only Memory. CD-ROM is a type of optical disk capable of storing large amounts of data – up to 1GB, although the most common size if 630MB. A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages. CD-ROMs are recorded by the vendor, and once recorded, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. Also called a CD-Rom drive, a CD-ROM player is a device that can read information from a CD-ROM.
CD-ROM players can be either internal, in which case they fit in a bay, or external, in which case they generally connect to the computer’s parallel port. Parallel CD-ROM players are easier to install, but they have several disadvantages: they are something more expensive than internal players, they use up the parallel port which means that you can’t use the port for another device such as a printer, and the parallel port itself may not be fast enough to handle all the data pouring through it.
Two more precise measurements are the drives seek time and data transfer rate. The seek time, also called the access time, measures how long, on average, it takes the drive to access a particular piece of information. The data transfer rate measures how much data can be read and sent to the computer in a second.
Almost all CD-ROMs conform to a standard size and format, so it is usually possible to load and type of CD into any ROM player. CD-ROMs are particularly well suited to information that requires large storage capacity.
CD-R DRIVE
CD-R drive, which is short for Compact Disk-Recordable drive, is a type of disk drive that can create CD-ROMs and audio CDs. A feature of many CD-R drives, called multisession recording, and enables you to keep adding data to a CD-ROM over time. This is extremely important if you want to use the CD-R drive to create backup CD-ROMs. To create CD-ROMs and audio CDs, you’ll need not only a CD-R drive, but also a CD-R software package.
CD-RW DISKS
CD-RW disk is short for CD-ReWritable disk and this is a new type of Cd disk that enables you to write onto it in multiple sessions. One of the problems with CD-R disks is that you can only write to them once. With CD-RW drives and disks, you can treat the optical disk just like a floppy or hard disk, writing data onto it multiple times. The first CD-RW drives became available in mid-1997. They can read CD-ROMs and can write onto today’s CD-R disks, but they cannot write on CD-ROMs.
|
Responses
|
No responses found. Be the first to respond and make money from revenue sharing program.
|
|
Watch TV Channels
|