Computer Networks

1. Computer Networks EEC 484 Instructor: Sanchita Mal-Sarkar

2. Computer • An electronic machine that accepts input, processes data, stores data, and produces output. • Data can be numbers, text, images, graphics, and sound, etc. • Computer program is a set of instructions. Without it computer is useless. • Programming languages allow us to write these instructions (e.g. C, C++, Java, etc).

3. Computer system • A computer system consists of a computer, peripheraldevices, and software. • The computer itself can take care of the processing function, but it needs additional components, called peripherals, to accomplish its input, output and storage functions. • Example of an internal peripheral device is hard disk drive.

4. Computer Hardware • Hardware is the physical component of a computer. • Hardware is the equipment used to perform the necessary computations. • Examples: • Main memory (RAM, ROM), secondary memory (hard disk drive, floppy disk drive), CPU, input devices (keyboard and mouse), and output devices (monitor and printer).

5. Hardware Components of a Computer System • Central Processing Unit (CPU) • Arithmetic-Logic Unit • Control Unit Input Devices Secondary Storage • Keyboard • Computer mouse • Touch screen • Source data automation • Magnetic disk • Optical disk • Magnetic tape Buses Output Devices • Printers • Video display terminals • Plotters • Audio output Communications Devices Primary Storage

6. Central Processing Unit (CPU) • Coordinates all computer operations. • Performs arithmetic and logical operations on data. • To process a program stored in main memory, • - CPU retrieves each instruction in sequence. • - Interprets the instruction to determine what should be done. • - Retrieves any data needed to carry out that instruction • - Then CPU performs the actual manipulation. • CPU’s current instruction and data values are stored temporarily inside the CPU in special high-speed memory locations called registers.

7. Central Processing Unit (CPU) • The CPU consists of a control unit and an arithmetic-logic unit. • Three kind of buses link the CPU, primary storage, and other devices in the computer systems. • The data bus moves data to and from primary storage. • The address bus transmits signals for locating a given address in primary storage. • The control bus transmits signals specifying whether to read or write data to or from a given primary storage address, input device, or output device.

8. Primary Storage 1 8 # T U Data Bus, Address Bus, and Control Bus Central Processing Unit (CPU) Arithmetic-Logic Unit 24 + 12 = 36 12 < 24 Control Unit Data Bus Address Bus Control Bus Output Devices Secondary Storage Input Devices

9. Computer Software • Software consists of the computer programs that allow us to solve problems by providing sets of instructions. • Examples: • DOS, Windows, Mac. Office family, Lotus, Netscape, Internet Explorer, Virus scans, tax programs, computer games, GUI - Graphical User Interface.

10. Computer Software • Computer hardware is useless without software. • Software is the set of instructions and associated data that direct the computer to do a task. • Software can be divided into two categories: -- System software and application software. • System software helps the computer to carry out its basic operating tasks. • Application software helps the user carry out a variety of tasks.

11. The major types of software System Software Operating Systems Schedules computer events Allocates computer resources Monitor events Application software System software Hardware Language translators Interpreters Compilers Users Application Software Programming languages Assembly language FORTRAN, BASIC, PL/1 PASCAL, C “4th generation “ languages Utility programs Routine operations (e.g. sort, list, print) Manage data (e.g. create files, merge files

12. System Software • Manages the fundamental operations of the computer, such as • loading programs and data into memory, • executing programs, • saving data to disks, • displaying information on the monitor, • and transmitting data through a port to a peripheral device. • Types of system software: operating systems, utilities, language translators.

13. Operating System • Collection of computer programs that control the interaction of the user and the computer hardware. • Responsible for directing all computer operations and managing all computer resources. • Controls basic input and output, allocates system resources, manages storage space, maintains security, and detects equipment failure. • A part of the operating system code is stored in a ROM and the rest of it resides on a disk. • Loading the operating system into memory is called booting the computer.

14. Responsibilities of an Operating System • Communicates with user, receives and executes commands, shows error messages. • Manages allocation of memory, processor time and other resources. • Collects input from keyboard, mouse, and provides data to running programs. • Conveys program output to screen, printer, or other output device. • Accesses data from secondary storage. • Writes data to secondary storage.

15. Application software • Developed for a specific task , such as word processing( MS Word/ WordPerfect), accounting (Lotus 1-2-3/ Excel), or database management (Access/ dBASE). • Most applications are purchased on diskette or CD-ROM. • They are installed by copying the programs from the diskettes/CD-ROM to the hard disk.

16. Data Communications • The transmission of text, numeric, voice, or video data from one machine to another is called data communications. • For example, Send an electronic mail to your friends around the globe. • The four essential components of data communications are a sender, a receiver, a channel, and a protocol. • Sender => The computer that originates the message is called the sender. • Receiver => The computer at the message’s destination is called the receiver.

17. Data Communications • Channel => The message needs some kind of medium to be transmitted. This medium is called channel. For example, telephone or coaxial cable, microwave signal, or optical fibers • Protocol => The rules that establish an orderly transfer of data between the sender and the receiver are called protocols. • Computer software and hardware establish these protocols at the beginning of the transmission, and both computers have to follow the protocols to ensure accurate transfer of data.

18. Networks • One of the most important types of data communications in the business world is a network connection. • A network connects one computer to another computers and peripheral devices to share data and resources. • There is a number of network configurations. local area network (LAN) => computers and peripheral devices are located relatively close to each other, generally in the same building. • Client/server networks =>Some networks have file servers (one or more computers) that act as the central storage location for programs and that provide mass storage for most of the data used on the network. A network with a file server is called a client/server networks.

19. Networks • Peer-to-peer networks => When a network does not have a file server, all the computers essentially are equal, and programs and data are distributed among them. This is called a peer-to-peer network. • Each computer that is part of the network must have a network interface card installed. This device creates a communication channel between the computer and the network. • Network software is also essential to establish the communications protocols. • Standalone computer => A microcomputer that is not connected to a network is called a standalone computer.

20. Telecommunications • Allows us to send and receive data over telephone lines. • A modem connects a computer to a telephone jack. • At the sending site, modem converts the digital signal from a computer into analog (continuous wave) signals (sound waves) that can traverse ordinary phone lines (modulation). • At the receiving site, a second modem converts the analog signals back into digital signals (demodulation).

21. Telecommunications

22. Internet • The internet was originally developed for the government to connect the researchers around the world to share data. • Today, the internet is the largest network in the world that connects millions of people in almost 200 countries. • The use of internet: • electronic mail => This is the capability to send a message from one user’s computer to another user’s computer where it is stored until the receiver opens it. Message passes through electronic links called gateways. • World Wide Web (Web) => Web is a huge database of information that is stored on the network servers in places that allow public access. The information is stored as text files called web pages.

23. Internet • Hyperlinks => a place on a computer screen that is programmed to connect to a particular file on the same network server, or on a network server on the other side of the globe. • Web browser => communication software that help us navigate the WWW is called web browsing software or web browser.