The central processing unit (CPU) Main memory, also known as random access memory (RAM)

1. The computer is a system in which programs (software) can execute with appropriate input data and produce desired results. • The central processing unit (CPU) • Main memory, also known as random access memory (RAM) • The storage devices • The main input/output (I/O) devices • Communication ports

2. First Generation - 1940-1956: Vacuum Tubes The first computers used vacuum tubes for circuitry and magnetic drums for memory, and were often enormous, taking up entire rooms. First generation computers relied on machine language. The UNIVAC and ENIAC computers are examples of first-generation computing devices.

3. Second Generation - 1956-1963: Transistors Transistors replaced vacuum tubes and ushered in the second generation of computers. These computers were smaller, faster, cheaper, more energy-efficient and more reliable Second-generation computers still relied on punched cards for input and printouts for output. These computers moved from cryptic binary machine language to symbolic, or assembly, languages.

4. Third Generation - 1964-1971: Integrated Circuits The development of the integrated circuit was the hallmark of the third generation of computers. Transistors were miniaturized and placed on siliconchips, called semiconductors. Computer processing speed drastically increased. keyboards and monitors were introduced in this generation. Computers for the first time became accessible to a mass audience because they were smaller and cheaper.

5. Fourth Generation - 1971-Present: Microprocessors thousands of integrated circuits were built onto a single silicon chip. The Intel 4004 chip, located all the components of the computer - from the central processing unit and memory to input/output controls - on a single chip. As these small computers became more powerful, they could be linked together to form networks.

6. Fifth Generation - Present and Beyond: Artificial Intelligence Fifth generation computing devices, based on artificial intelligence As a part of fifth generation feature voice recognition can be taken, that are being used today. Quantum computation and molecular and nanotechnology will radically change the face of computers in years to come. The goal of fifth-generation computing is to develop devices that respond to natural language input and are capable of learning and self-organization.

7. INPUT DEVICE:-Any machine that feeds data into a computer. For example, a keyboard is an input device. Other input devices are Mouse, trackballs etc. OUTPUT DEVICE:- Whereas a display monitor is an output device. Printer is another example of output device.

9. Keyboards: the most frequently used input devices, are used to enter instructions and data via keys. There are many variations on the layout and labeling of keys. Extra numeric keys may be added, as may special-purpose function keys, whose effects can be defined by programs in the computer.

10. Scanners:produce a digital image of a document for input and storage in a computer, using technology similar to that of a photocopier. Small scanners can be passed over the document surface by hand; larger versions have a flat bed, like that of a photocopier, on which the input document is placed and scanned.

11. MOUSE (Manually Operated Utility Service Equipment):A device that controls the movement of the cursor or pointer on a display screen. A mouse is a small object the user can roll along a hard, flat surface. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse's tail, and the fact that one must make it move along a surface. As the user moves the mouse, the pointer on the display screen moves in the same direction.

12. TRACKBALL: A trackball is a pointing device consisting of a ball held by a socket containing sensors to detect a rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor.

13. JOYSTICK: A joystick is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Joysticks are often used to control video games, and usually have one or more push-buttons whose state can also be read by the computer. A popular variation of the joystick used on modern video game consoles is the analog stick.

15. MONITOR: Another term for display screen. The term monitor, however, usually refers to the entire box, whereas display screen can mean just the screen. In addition, the term monitor often implies graphics capabilities 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. Color monitors can display anywhere from 16 to over 1 million different colors. Color monitors are sometimes called RGB monitors because they accept three separate signals -- red, green, and blue.

16. PRINTER: A device that prints text or illustrations on paper. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories: • DAISY WHEEL • DOT MATRIX • INK JET • LASER • LCD LED • LINE PRINTER • THERMAL PRINTER

17. LAPTOP: A laptop is a personal computer designed for mobile use. A laptop integrates most of the typical components of a desktop computer. They usually have a touch screen display and some include handwriting recognition or graphics drawing capability.

18. RAM A type of computer memory that can be accessed randomly. RAM is the most common type of memory found in computers There are two basic types of RAM: dynamic RAM (DRAM) static RAM (SRAM) .

19. ROM is a class of storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified, it is mainly used to distribute firmware. Modern semiconductor ROM chips are not immediately distinguishable from similar chips like RAM modules, except by the part numbers printed on the package.

20. Hard disk: Hard Disk drives (HDDs) for PCs generally have seek times of about 12 milliseconds or less. Many disk drives improve their performance through a technique called caching. it’s a sort of secondary memory where data can be stored permanently.

21. CPU:- central processing unit, is the brains of the computer. Sometimes referred to simply as the processor or central processor, In terms of computing power, the CPU is the most important element of a computer system. Two typical components of a CPU are: The arithmetic logic unit(ALU), which performs arithmetic and logical operations. The control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.

22. USE OF COMPUTER NETWORKS • NETWORKS FOR COMPANIES • RESOURCE SHARING (e-commerce) • HIGH RELIABILITY (backup facility) • SAVING MONEY (sending information, online shopping) • COMMUNICATION MEDIUM (EDI, EFT) • NETWORK FOR PEOPLE • ACCESS TO REMOTE INFORMATION (browsing sites) • INTERACTIVE ELECTRONIC ENTERTAINMENT (online movie) • PERSON TO PERSON COMMUNICATION (e-mail, chatting, video conferencing)

23. CLIENT MACHINE SERVER MACHINE CLIENT PROCESS SERVER PROCESS REQUEST NETWORK REPLY DEFINITION OF COMPUTER NETWORKS Definition:-the merging of computers and communications has had a profound influence on the way computer systems are organized. The concept of the “computer center” as a room with a large computer to which users bring their work for processing is now totally obsolete. The old model of a single computer serving all of the organization’s computational needs has been replaced by one in which a large number of separate but interconnected computers do the job. These systems are called computer networks.

24. BROADCASTING POINT-TO-POINT NETWORK HARDWARE • BROADCAST NETWORK : this has a single communication channel that is shared by all the machines on thenetwork. Short messages called packets in certain contexts, sent by any machines are received by all the others. • POINT-TO-POINT:It consists of many connections between individual pairs of machines. To go from the source to destination, a packet on this type of network may have to visit one or more intermediate machines.

25. NETWORK HARDWARE CLASSIFICATION OF INTERCONNECTED PROCESSORS BY SCALE

26. NETWORKTOPOLOGIES • STAR NETWORK • RING NETWORK • BUS NETWORK

27. Network Topology Star Network Topology Bus Network with Backbone Self-healing Ring Topology Two rings Token Ring Network Topology

28. DIFFERENT TYPES OF NETWORK • LAN • MAN • WAN • WIRELESS NETWORKS • INTERNETWORKS

29. LAN (LOCAL AREA NETWORK) • These are privately-owned networks within a single building or campus of upto a few kilometers in size. • They are widely used to connect personal computers and workstations In company offices and factories to share resources (printer) and exchange information. • Their size is small than other network. • Their transmission technology is developed than other networks. • They differ in the topology from other networks. computer Bus topology cable Ring topology

30. TOKEN RING TRANSMISSION

31. Direction of flow on bus A Bus A computer N 1 2 Head end MAN(METROPOLITAN AREA NETWORK) • It is basically the bigger version of LAN and normally uses similar technology. • It may cover a group of nearby corporate offices or a city. • It might be public or public. • It can support both data and voice. 3 Direction of flow on bus B

32. WAN (WIDE AREA NETWORK) router subnet host LAN • It spans a large geographical area. • It contains a collection of machines intended for running user programs. • The hosts (end systems) are connected by communication subnet. • The job of subnet is to carry messages from host to host. • In WAN we find circuits and switching elements. • The switching computers are generally called routers. RELATION BETWEEN HOSTS AND THE SUBNET

33. WIRELESS NETWORK • Mobile networks, such as notebook computers and personal digital assistants (PDAs) and the fastest-growing segment of the computer industry.

34. INTERNET • Many networks exist in the world, often with different hardware and software. People connected to one network often want to communicate with people attached to a different one. This desire requires connecting together different, and frequently incompatible networks, sometimes by using machines called gateways to make the connections and provide the necessary translation, both in terms of hardware and software. A collection of interconnected networks is called an internetwork or simply internet.

35. Internet

36. NETWORK SOFTWARE • To reduce their design complexity, most networks are organized as a series of Layers or levels, each one built upon the one below it. • The number of layers, the name of each layer, and the function of each layer differ from network to network. • Layer non one machine carries on a conversation with layer n on another machine. • The rules and conventions used in this conversation are collectively known as the layer n protocol. • A protocol is an agreement between the communicating parties on how communication is to proceed. • The entities comprising the corresponding layers on different machines are called peers. • The peers communicate using the protocol. • No data is transferred from layer n on one machine to layer n on another machine. • Instead each layer passes data and control information to the layer immediately below it, until the lowest layer is reached. • Below layer 1 is the physical medium through which actual communication occurs. • Between each pair of adjacent layers there is an interface. • A set of layers and protocols is called a network architecture. • A list of protocols used by a certain system, one protocol per layer is called a protocol stack.

37. NETWORK SOFTWARE Layer 5 protocol Layer 5 Layer 5 Layer 4/5 interface Layer 4 protocol Layer 4 Layer 4 Layer 3/4 interface Layer 3 protocol Layer 3 Layer 3 Layer 2/3 interface Layer 2 protocol Layer 2 Layer 2 Layer 1/2 interface Layer 1 protocol Layer 1 Layer 1 Physical medium Host 1 Host 2

38. PROTOCOL HIERARCHIES • A message M, is produced by an application process running in layer 5 and is given to layer 4 for transmission. • Layer 4 puts a header in front of the message to identify the message and passes this result to layer 3. • Layer 3 breaks up the incoming messages into smaller units, packets, and adds the layer 3 header to each packets. It decides which of the outgoing line to use and passes the packet to layer 2. • Layer 2 adds the header and as well as the trailer and gives the resultant packet to layer1. • Layer 1 passes the message received by layer2 and transmits it to physical medium to send the message to the destination machine. • At the receiving machine the messages moves upwards, and the header and trailers are stripped off as it progresses. • None of the headers for layers below layer n are passed up to layer n.

39. PROTOCOL HIERARCHIES • There is a basic difference between virtual and actual communication. • The peer processes in layer 4 use the layer 4 protocol. • This procedure is called SendToOtherSide and GetFromOtherSide, followed in virtual communication. • But actual communication follows the interface protocol.

40. M M 5 4 3 H4 M H4 M H3 M2 H3 H3 M2 H4 T2 M1 H3 M2 H3 H3 H2 H3 H3 M2 H4 H4 M1 H4 M1 T2 H2 H2 2 H2 T2 M1 T2 1 PROTOCOL HIERARCHY Layer 5 protocol Layer 4 protocol Layer 3 protocol Layer 2 protocol Source machine Destination machine EXAMPLE INFORMATION FLOW SUPPORTING VIRTUAL COMMUNICATION IN LAYER 5