Cyber Law - Cyberlaws Course Material -
Basics of Computers and Internet
Cyber Smart Home Page
Basics of the world of computers
|
|
What is a computer? A computer is an electronic device that executes the instructions in a program. A computer has four functions: a. accepts data Input b. processes data processing c. produces output Output d. stores results Storage The above is the Information Processing Cycle Basic terminology Hardware the physical parts of the computer. Software the programs (instructions) that tell the computer what to do Data individual facts like first name, price, quantity ordered Information data which has been massaged into a useful form, like a complete mailing address Default the original settings; what will happen if you don't change anything. Distributed or Grid Computing The power needed for some calculations is more than even a single supercomputer can manage. In distributed computing using a PC grid many computers of all sizes can work on parts of the problem and their results are pooled. SETI@Home project looks for signs of intelligent communication in radio signals coming from space. (SETI stands for Search for Extra-Terrestrial Intelligence.) Entropia: Fighting AIDS @Home-modeling evolution of resistance to drugs and designing better AIDS treatments Folding @home-working on how proteins fold, which is important to understanding how they work and reproduce Distributed. Net-cryptography and mathematical problems GOLEM@Home completed: evolving robots (Genetically Organized Lifelike Electro Mechanics) PiHex calculating the value of Pi to certain large places (done!) Server Server The term server actually refers to a computer's function rather than to a specific kind of computer. A server runs a network of computers. It handles the sharing of equipment like printers and the communication between computers on the network. For such tasks a computer would need to be somewhat more capable than a desktop computer. It would need: more power larger memory larger storage capacity high speed communications APPLICATION An application is another word for a program running on the computer. Whether or not it is a good application depends on how well it performs the tasks it is designed to do and how easy it is for the user to use. That involves the user interface- the way the user tells the software what to do and how the computer displays information and options to the user. Text Interfacec:\>pkzip c:\myfiles\newfile.zip c:\docs\report14.doc Text Interface with Menus Graphical Interface Word processing is the most used computer application! Other Applications For professional publications, a desktop publishing program gives the precise control needed and also advanced capacities such as preparing four-color separations for commercial printing A spreadsheet is the application of choice for most documents that organize numbers, like budgets, financial statements, grade sheets, and sales records. A spreadsheet can perform simple or complex calculations on the numbers you enter in rows and columns. Some popular spreadsheets include MS Excel, Lotus 1-2-3, and Quattro Pro. A database is a collection of data that you want to manage, rearrange, and add to later. It is a good program to use to manage lists that are not entirely numbers, such as addresses and phone numbers, inventories, and membership rosters. Some popular databases include MS Access, dBase, FoxPro, Paradox, Approach, and Oracle Communications These programs temporarily connect computers to each other to exchange information. They may use telephone lines or dedicated cables for the connection. A communications program includes one or more of the following actions: sending and receiving files: FTP (File Transfer Protocol) exchanging messages in a group: chat programs private messages: instant messaging voice messages video conferencing phone calls over the Internet FTP (File Transfer Protocol) An FTP program manages the moving of files between computers. When you download a file over the Internet, you are using an FTP program. Programs like word processors and HTML editors that can upload files to web sites include this ability without having to use another program Integrated software combines the functions of several programs into one interface. Such a program is usually designed for the beginning or casual user. Many advanced features are omitted that might be found in stand-alone products. For example, the word processor in an integrated software package would not likely have a way to automatically generate a table of contents and would have fewer options on how to handle footnotes, headers, and footers. Microsoft Works is an example of integrated software. A software suite is a set of applications which can each stand alone. They are packaged together for a lower price than if all were bought separately. There are usually enhancements that help the applications communicate with each other, also. Some popular suites of office software include MS Office, Lotus Smart Suite, and WordPerfect Office Types of characters read with special devices Bar Codes- Retail shops now use printed bar codes on products to track inventory and calculate the sale at the checkout counter. The US Post Office uses bar codes to sort mail, but the bars are different from those used for pricing products. Optical Marks- example - test scoring A special machine "reads" the marks. Woe to the student who takes a test with this kind of score sheet and doesn't get those bubbles colored in correctly! Magnetic Ink- Bank account # is printed in special ink with magnetic qualities which can be read by the right machine. Optical Characters- There are coding systems that use letters or special characters that are especially shaped to be easy for machines to read. OCR software Optical Character Recognition: This software takes a scanned image and converts the characters in the image into computer characters. The document can now be edited with a word processor. This is a very tricky process. Documents must be carefully checked for wrong conversions. If the original print was not very crisp and clean, errors are very likely. Manually checking for proper translation is necessary. These programs are getting really good if they have a clear scan to work with. Digital Data Modern computers are digital, that is, all info is stored as a string of zeros or ones - off or on. All the thinking in the computer is done by manipulating these digits. The concept is simple, but working it all out gets complicated. 1 bit = one on or off position 1 byte = 8 bits So 1 byte can be one of 256 possible combinations of 0 and 1. Numbers written with just 0 and 1, are called binary numbers. Each 1 is a power of 2 so that the digits in the figure represent the number: = 2 raised to power 7 + 0 + 2 raised to power 5 + 0 + 2 raised to power 3 + 2 raised to power 2 + 0 +0 = 128 +0 +32 + 0 + 8 + 4 + 0 + 0 = 172 Every command and every input is converted into digital data, a string of 0's and 1's. CPU The CPU, or Central Processing Unit, is the part of the computer where work gets done. In most computers, there is one processing chip. Main Memory stores the commands that the CPU executes and the results. Control Unit This is the part of the computer that controls the Machine Cycle. It takes numerous cycles to do even a simple addition of two numbers ALU stands for Arithmetic/Logic Unit This is the part that executes the computer's commands. A command must be either a basic arithmetic operation: + - * / or one of the logical comparisons: > < = not =. Everything else has to be broken down into these few operations. Only one operation is done in each Machine Cycle. The ALU can only do one thing at a time but can work very, very fast. Diagrammatic representation-CPU Control Unit This is the part of the computer that controls the Machine Cycle. It takes numerous cycles to do even a simple addition of two numbers. Fetch -get an instruction from Main Memory Decode -translate it into computer commands Execute -actually process the command Store -write the result to Main Memory Operating System This is the instructions that the computer uses to tell itself how it "operates". It's the answer to "Who am I and what can I do?" Some common operating systems are DOS, various versions of Windows, OS/2, UNIX, LINUX, System 7. These all behave in very different ways and have different hardware requirements. So they won't all run on all machines Applications These are the various programs that are currently running on the computer. By taking turns with the Machine Cycle, modern computers can have several different programs running at once. This is called multi-tasking. Each open application has to have some data stored in Main Memory Storage in Memory Input/Output Storage When you enter new data, the keystrokes must be stored until the computer can do something with the new data. When you want data printed out or displayed, it must be stored somewhere handy first Working Storage The numbers and characters that are the intermediate results of computer operations must be stored until the final values are calculated. These values "in progress" are kept in temporary locations. For example, if the computer is adding up the numbers 3, 5, and 6, it would first add 3 to 5 which yields a value of 8. The 8 is stored in working storage. Then the 8 and 6 are added and the new value 14 is stored. The value of 14 is now available to be displayed on the screen or to be printed or to be used in another calculation. Unused Storage One hopes that there is always some storage space that is not in use. If space runs out in Main Memory, the computer will crash, that is, stop working. There are programs that sense when space is getting short and warn the user. The user could then close some of the open applications to free up more space in Main Memory Memory address A memory address holds 1 byte of data where 1 bit =0 or 1, on or off 1 byte = 8 bits 1 kilobyte (K or KB) =1024 bytes 1 megabyte (MB) =1024 kilobytes Processor Speed affected by: System clock rate = rate of an electronic pulse used to synchronize processing (Only one action can take place between pulses.) Measured in megahertz (MHz) where 1 MHz = 1 million cycles per second or gigahertz (GHz) where 1 GHz = 1 billion cycles per second. This is what they are talking about if they say a computer is a 2.4 GHz machine. It's clock rate is 2.4 billion cycles per second. Bigger number = faster processing Bus width = the amount of data the CPU can transmit at a time to main memory and to input and output devices. (Any path bits travel is a bus.) An 8-bit bus moves 8 bits of data at a time. Bus width can be 8, 16, 32, 64, or 128 so far. Word size = a word is the amount of data the CPU can process at one time. An 8-bit processor can manipulate 8 bits at a time. Processors can be 8-, 16-, 32-, or 64-bit so far Processing: Physical Components There are several physical components of a computer that are directly involved in processing. The processor chip itself, the memory devices, and the motherboard are the main ones. Microprocessor- a single silicon chip containing CPU, ALU, and some memory. The ROM (Read Only Memory) cannot be changed by the user and contains the minimum instructions the computer needs to get started, called booting. There may also be another chip dedicated to calculations. The microprocessor chip is located on a large circuit board called the main board or motherboard. Memory Devices: Vacuum tube -oldest type. Didn't hold up long and generated a lot of heat.Core -small metal rings. Magnets tip a ring to left or right, which represents on and off. Relatively slow. Semiconductor - integrated circuit on a chip. This is what modern computers use for memory. The capacity of a memory chip is measured in megabytes. Sizes are measured in megabytes and come in powers of 2: 1, 4, 8, 16, 32, 64, 128, 256, 512 MB etc. on one memory board. Several such boards can be installed in the computer to increase the amount of RAM (Random Access Memory) available as Main Memory. Printers How fast? The speed of a printer is measured in: cps= characters per secondlpm= lines per minute ppm= pages per minute What print quality? Impact Printers-Dot Matrix , Daisy Wheel , Chain and Band Printers, Non-Impact Printers-Ink Jet, Thermal, Page Printer Screen from "computer screen" or "display screen“ Monitor from its use as a way to "monitor" the progress of a program VDT= video display terminal from early network terminals CRT= cathode ray tube from the physical mechanism used for the screen. VDU= visual display unit to cover all the mechanisms from desktop CRTs to LCD flat screens on laptops to LED screen on palmtops Size , Resolution , Refresh Rate , Type , Color , Reverse video , Cursor/ Pointer ,Scrolling Type of Screens Monochrome one color text on single color background, i.e. white letters on blue, or green characters on black Color various colors can be displayed. (This one is easy!) CRT The most common type of monitor, which uses a cathode ray tube. Liquid Crystal Display (LCD)Used in laptops esp. Large flat monitors are becoming affordable, especially if you do not have desk space for a large CRT monitor. Plasma Screens Used for very large screens and some laptops. Flat, good color, but quite expensive Main Memory = Primary Storage Auxiliary Storage = Secondary Storage Auxiliary storage holds what is not currently being processed. This is the stuff that is "filed away", but is ready to be pulled out when needed. It is nonvolatile, meaning that turning the power off does not erase it. Auxiliary Storage is used for: Input - data and programs Output - saving the results of processing Protecting computer data Write protect , Hard disks and devices without a switch: Make files Read-Only and/or Hidden to keep them from being overwritten ,Backup, Anti-virus Use an antivirus program continuously. Computer viruses are sneaky computer programs that can erase your data and even your whole system. Most viruses are merely annoying and are created as practical jokes. But there are a number of very damaging viruses out there. Your computer gets a virus by downloading an infected file from the internet or your office network, or by first using a floppy in an infected computer and then accessing a file on that floppy with your own computer. This makes it difficult to keep a virus from spreading. Magnetic tape uses a method similar to that of VCR tape for storing data. The speed of access can be quite slow, however, when the tape is long and what you want is not near the start. So this method is used primarily for major backups of large amounts of data. Businesses especially might do a backup of the day's transactions every day and a backup of the whole system once a week or so. Keeping sets of backups like this minimizes the amount of data loss when the computer system goes down. Optical Disks An entirely different method of recording data is used for optical disks. These include the various kinds of CD and DVD discs. How optical disks are similar Formed of layers Data in a spiral groove on starting from the center of the disk Digital data (1's and 0's) 1's and 0's are formed by how the disk absorbs or reflects light from a tiny laser. The different types of optical disks use different materials and methods to absorb and reflect the light. Advantages of Optical Disks Physical: An optical disk is much sturdier than tape or a floppy disk. It is physically harder to break or melt or warp. Delicacy: It is not sensitive to being touched, though it can get too dirty or scratched to be read. It can be cleaned! Magnetic: It is entirely unaffected by magnetic fields. Capacity: Optical disks hold much more data than floppy disks. Communications Channel A communications channel, also called a communications line or link, is the path that the data follows as it is transmitted from one computer to another. a communications channel at work. A PC is sending a message to a host computer clear across the country. Notice the variety of transmission methods used: telephone lines, satellite links, microwave relay Data Communications for transmission of data and information over a communications channel Telecommunications for any long-distance communications, especially television Teleprocessing for accessing computer files located elsewhere Transmission media Transmission media just means the physical materials that are used to transmit data between computers. Cable For communications between computers that are linked by cable, there are three choices. Twisted wire(phone line) Coaxial cable(round insulated wire) Fiber optic line(glass fibers) Broadcast For longer distances or when cables are not practical, other transmission media come into play Wireless (infrared, light, radio) Microwave Satellite Three bands of communication channels-Narrow: 40-100 bps like Telegraph lines Voice: 110-9600 bps like telephone lines ,Broad: several mbps like microwave ,fibre optics, satellite communication Modems Signals Two types of signals are used for data transmission: Digital and Analog. A digital signal is a stream of 0's and 1's. So this type is particularly appropriate for computers to use. An analog signal uses variations (modulations) in a signal to convey information. It is particularly useful for wave data like sound waves. Analog signals are what your normal phone line and sound speakers use. Modems Often communications between computers use the telephone system for at least part of the channel. A device is needed to translate between the analog phone line and the digital computer. Such a device is the modem, which comes from Modulate/Demodulate, which is what a modem does. It modulates a digital signal from the computer into an analog one to send data out over the phone line. Then for an incoming signal it demodulates the analog signal into a digital one. Digital The rate of digital transmission is measured in bits per second (bps). Common rates for regular modems are 28.8 Kbps, 33.6 Kbps, and 56 Kbps where the K stands for thousand. Analog The analog side is measured in baud where 1 baud is one change in the signal per second. Most people use bps and baud as though they were the same. Physical types There are three physical types of modems: External which plugs into a serial port on the back of the computer , Internal where the phone line plugs directly into card through the back of the computer Softwares Dialing Dialing software tells the computer how to place a call on the phone line connected to it. It also displays messages about the progress of the call or lack thereof. File Transfer One of the most common uses of computer to computer communications is to transfer files from one to the other. Terminal Emulation Programs running on a network or that connect to a computer bulletin board (BBS), Data encryption softwares A LAN is a Local Area Network. This would include networks where the computers are relatively close together. So LANs would be within the same office, a single building, or several buildings close together. Most popular LAN is the Ethernet. cable length 100m,speed of data transfer 1000mbps A WAN is a Wide Area Network, which would be all networks too large to be LANs. There doesn't seem to be a clear line between the two designations. A WAN would be most useful for large companies with offices or factories in widely separated areas, like Microsoft, IBM, Ford, AT&T, etc. linked by telecommunication or microwave links-high cost involved. Network Configurations Each device in the network, whether it's a computer, printer, scanner, or whatever, is called a node. The star pattern connects everything to one host, which is the computer that handles the network tasks and holds the data. All communications between computers go through the host. This configuration is good for businesses that have large amounts of rapidly changing data, like banks and airline reservation offices. Bus The bus pattern connects the computer to the same communications line. Communications goes both directions along the line. All the computers can communicate with each other without having to go through the server. Advantages:Any one computer or device being down does not affect the others.Disadvantages: Can't connect a large number of computers this way. It's physically difficult to run the one communications line over a whole building Ring The ring pattern connects the computers and other devices one to the other in a circle. There is no central host computer that holds all the data. Communication flows in one direction around the ring. This configuration is good when the processing of data can be done on the local PC. Advantages:Requires less cabling and so is less expensive. Disadvantages:If one node goes down, it takes down the whole network. Connecting Networks Networks can be connected to each other, too A gateway connects networks of different kinds, like connecting a network of PCs to a main frame network A bridge connects networks of the same type. This job is simple. A router connects several networks. A router is smart enough to pick the right path for communications traffic. If there is a partial failure of the network, a router looks for an alternate route. software is a catch-all term for the programs that handle the running of your computer's hardware. The two main categories are: operating systems utility programs Operating Systems Between the hardware and the application software lies the operating system. The operating system is a program that conducts the communication between the various pieces of hardware like the video card, sound card, printer, the motherboard and the applications. All operating systems must handle the same basic tasks. These functions can be divided into three groups: Allocate resources, manage disks and files, monitor activities There are two basic types of operating systems: single program and multitasking. Common Operating Systems -MS-DOS, Microsoft's Disk Operating System , Windows 95 and Windows 98 , Windows Me (Windows Millennium Edition) is an upgrade of Windows 98, release date Sept. 14, 2000 Windows NT (the NT apparently came from New Technology) is an operating system for client-server type networks. The latest version of NT has a user interface that is practically identical to Windows 95. Since Windows NT is designed for the higher demands of networks, it has higher demands itself for disk space and memory. Windows 2000 is an upgrade of Windows NT rather than of Windows 98 Windows CE is for small devices like palmtop and handheld computers The Apple Macintosh is a multitasking operating system that was the first graphical interface to achieve commercial success IBM's 32-bit operating system is OS/2. This is a popular system for businesses with complex computer systems from IBM. It is powerful and has a nice graphical interface. UNIX is an operating system developed by Bell Labs to handle complex scientific applications. University networks are likely to use UNIX, as are Internet Service Providers Linux is an operating system similar to UNIX that is becoming more and more popular. (And it has the cutest logo!) It is a open-source program created by Linus Torvalds at the University of Finland, starting in 1991 Utility Programs perform tasks related to the maintaining of your computer's health - hardware or data. Some are included with the operating system. Programming What is a computer program? Simply put, a computer program is a set of detailed directions telling the computer exactly what to do, one step at a time. A program can be as short as one line of code, or as long as several millions lines of code Language Types Machine Languages The language of the CPU (The central processing unit of the computer, which is the part that does the "thinking"). The lowest level language. Composed of 0's and 1's Assembly Languages Abbreviations for machine language High-Level Languages Use program statements - words and algebra-type expressions. Developed in the 50's and 60's.After a program is written in one of the high-level languages, it must be either compiled or interpreted. A compiler program rewrites the program into machine language that the CPU can understand. This is done all at once and the program is saved in this new form. A compiled program is generally considerably larger than the original. An interpreter program translates the program statements into machine language one line at a time as the program is running. An interpreted program will be smaller than a compiled one but will take longer to execute.4th Generation Languages = 4GL. Very high-level languages. These are results oriented and include database query languages. There are fewer options for programmers, but the programs are much easier to write than in lower level languages. These too must be compiled or interpreted. Development A program goes through the following steps over and over during its development, never just once. Set & Review goals: What is it supposed to do? Design: Create the strategy to achieve goal. Coding: Write the program. Testing: Try it out with real people. Documentation: What you did and why. How to use it. Courtesy : Karnika Seth
|