Wireless Network-Wi-Fi, WI-Max, Bluetooth

Wireless Network

In computer networking, wireless technology is a modern alternative to networks that use cables. A wireless network transmits data by microwave and other radio signals. Wireless network refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes are implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network.

A wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication.

Here's what happens:

1. A computer's wireless adapter translates data into a radio signal and transmits it using an antenna.
2. A wireless router receives the signal and decodes it. The router sends the information to the Internet using a physical, wired Ethernet connection.

The process also works in reverse, with the router receiving information from the Internet, translating it into a radio signal and sending it to the computer's wireless adapter.

Wi-Fi (Wireless Fidelity)

The term Wi-Fi stands Wireless Fidelity Wi-Fi is a trademark of the Wi-Fi Alliance that manufacturers may use to brand certified products that belong to a class of wireless local area network (WLAN) devices based on the IEEE 802.11(Institute for Electrical and Electronic Engineers) standards, which is by far the most widespread WLAN class today. Because of the close relationship with its underlying standard, the term Wi-Fi is often used as a synonym for IEEE 802.11 technology.

The Wi-Fi Alliance, a global association of companies, promotes WLAN technology and certifies products if they conform to certain standards of interoperability. Not every IEEE 802.11-compliant device is submitted for certification to the Wi-Fi Alliance, sometimes because of costs associated with the certification process. The lack of the Wi-Fi logo does not necessarily imply a device is incompatible with Wi-Fi devices.

A Wi-Fi enabled device such as a personal computer, video game console, mobile phone, MP3 player or personal digital assistant(PDA) can connect to the Internet when within range of a wireless network connected to the Internet. The coverage of one or more (interconnected) access points — called hotspots — can comprise an area as small as a few rooms or as large as many square miles.

• They transmit at frequencies of 2.4 GHz or 5 GHz. This frequency is considerably higher than the frequencies used for cell phones, walkie-talkies and televisions. The higher frequency allows the signal to carry more data.
• They use 802.11 networking standards, which come in several flavors:

1. 802.11a transmits at 5 GHz and can move up to 54 megabits of data per second. It also uses orthogonal frequency-division multiplexing (OFDM), a more efficient coding technique that splits that radio signal into several sub-signals before they reach a receiver. This greatly reduces interference.

2. 802.11b is the slowest and least expensive standard. 802.11b transmits in the 2.4 GHz frequency band of the radio spectrum. It can handle up to 11 megabits of data per second, and it uses complementary code keying (CCK) modulation to improve speeds.

3. 802.11g transmits at 2.4 GHz like 802.11b, but it's a lot faster -- it can handle up to 54 megabits of data per second. 802.11g is faster because it uses the same OFDM coding as 802.11a.

4. 802.11n is the newest standard that is widely available. This standard significantly improves speed and range. For instance, although 802.11g theoretically moves 54 megabits of data per second, it only achieves real-world speeds of about 24 megabits of data per second because of network congestion. 802.11n, however, reportedly can achieve speeds as high as 140 megabits per second. The standard is currently in draft form -- the Institute of Electrical and Electronics Engineers (IEEE) plans to formally ratify 802.11n by the end of 2009.

Personal Computer Memory Card International Association (PCMCIA)
DSL (Digital Subscriber Line)

WiMAX (Worldwide Interoperability for Microwave Access)

WiMAX (Worldwide Interoperability for Microwave Access) is a telecommunications protocol that provides fixed and fully mobile internet access. The current WiMAX provides speed up to 40 Mbit/s. The name "WiMAX" was created by the WiMAX Forum, which was formed in June 2001 to promote conformity and interoperability of the standard. The forum describes WiMAX[ as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL".
WiMAX refers to implementations of the IEEE 802.16 wireless-networks standard (ratified by the WiMAX Forum), in similarity with Wi-Fi, which refers to interoperable implementations of the IEEE 802.11 Wireless LAN standard (ratified by the Wi-Fi Alliance). The WiMAX Forum certification allows vendors to sell their equipment as WiMAX (Fixed or Mobile) certified, thus ensuring a level of interoperability with other certified products, as long as they fit the same profile.

The IEEE 802.16 standard forms the basis of 'WiMAX' and is sometimes referred to colloquially as "WiMAX", "Fixed WiMAX", "Mobile WiMAX", "802.16d" and "802.16e."

Clarification of the formal names are as follow:

• 802.16-2004 is also known as 802.16d, which refers to the working party that has developed that standard. It is sometimes referred to as "Fixed WiMAX," since it has no support for mobility.
• 802.16e-2005, often abbreviated to 802.16e, is an amendment to 802.16-2004. It introduced support for mobility, among other things and is therefore also known as "Mobile WiMAX".

A WiMAX system consists of two parts:

• A WiMAX tower, similar in concept to a cell-phone tower - A single WiMAX tower can provide coverage to a very large area -- as big as 3,000 square miles (~8,000 square km).

• A WiMAX receiver - The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.

WiMAX provide two forms of wireless service:

• There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range -- 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions -- they are better able to diffract, or bend, around obstacles.

• There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it's able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth.

Uses of WiMAX

The bandwidth and range of WiMAX make it suitable for the following potential applications:

• Providing portable mobile broadband connectivity across cities and countries through a variety of devices.
• Providing a wireless alternative to cable and DSL for "last mile" broadband access.
• Providing data, telecommunications (VoIP) and IPTV services .
• Providing a source of Internet connectivity .

Comparison with Wi-Fi

Comparisons and confusion between WiMAX and Wi-Fi are frequent because both are related to wireless connectivity and Internet access.

1. WiMAX is a long range system, covering many kilometres, that uses licensed or unlicensed spectrum to deliver connection to a network, in most cases the Internet.

2. Wi-Fi uses unlicensed spectrum to provide access to a local network.
3. Wi-Fi is more popular in end user devices.

4. Wi-Fi runs on the Media Access Control's CSMA/CA protocol, which is connectionless and contention based, whereas WiMAX runs a connection-oriented MAC.

Wi-Fi and WiMAX are complementary. WiMAX network operators typically provide a WiMAX Subscriber Unit which connects to the metropolitan WiMAX network and provides Wi-Fi within the home or business for local devices (e.g., Laptops, Wi-Fi Handsets, smartphones) for connectivity. This enables the user to place the WiMAX Subscriber Unit in the best reception area (such as a window), and still be able to use the WiMAX network from any place within their residence.

Bluetooth

The heart of the Bluetooth brand identity is the name, which refers to the Danish king Harald "Bluetooth" Blatand who unified Denmark and Norway. In the beginning of the Bluetooth wireless technology era, Bluetooth was aimed at unifying the telecom and computing industries.

Bluetooth is an open wireless technology standard for exchanging data over short distances (using short length radio waves) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Created by telecoms vendor Ericsson in 1994, it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization. Today Bluetooth is managed by the Bluetooth Special Interest Group.

Bluetooth is a packet-based protocol with a master-slave structure. One master may communicate with up to 7 slaves in a piconet; all devices share the master's clock. Packet exchange is based on the basic clock, defined by the master, which ticks at 312.5 µs intervals. Two clock ticks make up a slot of 625 µs; two slots make up a slot pair of 1250 µs. In the simple case of single-slot packets the master transmits in even slots and receives in odd slots; the slave, conversely, receives in even slots and transmits in odd slots. Packets may be 1, 3 or 5 slots long but in all cases the master transmit will begin in even slots and the slave transmit in odd slots.

Bluetooth networking transmits data via low-power radio waves. It communicates on a frequency of 2.45 gigahertz (actually between 2.402 GHz and 2.480 GHz, to be exact). This frequency band has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).
Bluetooth can connect up to eight devices simultaneously. With all of those devices in the same 10-meter (32-foot) radius, you might think they'd interfere with one another, but it's unlikely. Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum.

Network Topologies

Network Topologies

In computer networking, topology refers to the layout, shape or structure of connected devices. This shape does not necessarily correspond to the actual physical layout of the devices on the network.

Network topologies are categorized into the following basic types:
1. Bus Topology
2. Ring Topology
3. Star Topology
4. Tree Topology
5. Mesh Topology

Bus Topology

 Uses single cable called Backbone to connect all device
 To communicate the device broadcast the message
 The message is seen by all the device
 The message is accepted by the recipient only

Bus networks use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options many years ago for bus topologies. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

Advantages of a Linear or Bus Topology
• Easy to connect a computer or peripheral to a linear bus.
• Requires less cable length than a star topology.

Disadvantages of a Linear or Bus Topology
• Entire network shuts down if there is a break in the main cable.
• Terminators are required at both ends of the backbone cable.
• Difficult to identify the problem if the entire network shuts down.

Ring Topology

 It is in the shape of ring as name suggest
 Token is used send message
 Message travel in either "clockwise" or "counterclockwise" but not in both direction

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.
To implement a ring network, one typically uses FDDI (Fiber Distributed Data Interface), SONET (Synchronous Optical Network), or Token Ring technology. Ring topologies are found in some office buildings or school campuses.

Star Topology

 It is widely used network topology
 The shape of star topology resemble the shape of star
 Hub is used to connect the device

Many home networks use the star topology. A star network features a central connection point called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Advantages of a Star Topology
• Easy to install and wire.
• No disruptions to the network then connecting or removing devices.
• Easy to detect faults and to remove parts.

Disadvantages of a Star Topology
• Requires more cable length than a linear topology.
• If the hub or concentrator fails, nodes attached are disabled.
• More expensive than linear bus topologies because of the cost of the concentrators.
The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called the star-wired ring.

Tree Topology

 Hub is used as root of the tree
 It follows hierarchical structure
 Only hub connect with each other directly
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus , and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub connection points) alone.

Advantages of a Tree Topology
• Point-to-point wiring for individual segments.
• Supported by several hardware and software venders.

Disadvantages of a Tree Topology
• Overall length of each segment is limited by the type of cabling used.
• If the backbone line breaks, the entire segment goes down.
• More difficult to configure and wire than other topologies.

Mesh Topology

 Most difficult to implement and costly
 Every device is connected with each other
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that even in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, most notably the Internet, employ mesh routing.
A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.

IP Addressing

Correct IP Addresses are Critical

On a TCP/IP based internetwork, the IP address is used to uniquely identify each device operating the TCP/IP protocols.

If the IP address is not correct, or you use an IP address already used somewhere else on the internetwork, your node will not work. It is critical to get the IP address settings correct to ensure you can communicate.

 

IP Address Size and Format

The IP Address Size and Format is as follows:

• 32 bits in size.

• Grouped into 8-bit bytes or octets.

• Decimal digits separated by dots, occurring at the octet boundaries eg. X.X.X.X.

• Divided into two portions - a network portion and a host portion.

 

Network Portion

The network portion of the IP address is used to identify the network segment that the Linux box is connected to. In an Ethernet network, this segment is the complete 10Base2 network, or the group of 10BaseT nodes connected to the same hub(s).

If you have a permanent connection to the Internet, the network portion of the IP address is indirectly allocated to you by the Internet Network Information Center (InterNIC). It is indirectly allocated because your ISP (Internet Service Provider) was given the network number by InterNIC, and your ISP allocated it to you.

Network Classes

The network portion of the IP address is divided up into 5 different classes or catagories.

This network class specifies how many bytes or octets of the IP address is used for the network portion, and how many octets are left for the host portion.

Class Definitions

 

The classes are as follows:

• Class A - The first octet of the IP address is used for the network portion, and the last three octets are used for the host portion.

• Class B - The first two octets of the IP address are used for the network portion, and the last two octets are used for the host portion.

• Class C - The first three octets of the IP address are used for the network portion, and the last octet is used for the host portion.

• Class D - Class D addresses are special addresses used for a special type of IP packet transmitting called Multicasting. You should not use a Class D network number when setting up your network.

• Class E - This class of network address is reserved for experimental purposes by the Internet Engineering Task Force. You should not use a Class E network address - you could be kicked off the Internet.

 

There are two things to notice about the above class definitions:

• Only Classes A, B, and C are valid for use when giving a host an IP address.

• The more octets available for the network portion of the IP address, the more networks exist, and the more octets available for the host portion of the IP address, the more hosts per network exist.

 

Within the total IP address space,

o there are only a small number of Class A networks (1 octet), but each class A network can have a huge number of hosts (3 octets),

o there are more Class B networks (2 octets), but each Class B network has less hosts (2 octets) than a Class A,

o And there are a huge number of Class C networks (3 octets), but each Class C network can only have a small number of hosts (1 octet).

Class Ranges

 

You can tell the Class of network address by looking at the first octet of the IP address.

• Class A - ranges from 1 to 127

• Class B - ranges from 128 to 191

• Class C - ranges from 192 to 223

Host Portion

Once you have your network number specified, you can now allocate the host portion of the IP address.

The host portion of the IP address must be uniquely assigned to each host within the network segment you are configuring. If you allocate the same IP address to two hosts connected to the same network segment, you will suffer from the "Duplicate IP Address" problem, which will cause intermittent communication between the involved hosts.

Under normal circumstances, octets in the host portion of the IP address can range from 0 through to 255, with some exceptions. These special exceptions will be discussed later.

 

IP Address Ranges

Based on the above discussion of the network and host portions of the IP address, the following ranges of IP address are available for Class A, B and C networks:

• Class A - 1.0.0.1 to 127.255.255.254

• Class B - 128.0.0.1 to 191.255.255.254

• Class C - 192.0.0.1 to 223.255.255.254

Computer Network

Computer network




Definition: A computer network, often simply referred to as a network, is a collection of computers and devices connected by communications channels that facilitates communications among users and allows users to share resources with other users. A computer network allows sharing of resources and information among devices connected to the network.

Need of Computer Network

Computer networks can be used for several purposes:

1. Facilitating communications. Using a network, people can communicate efficiently and easily via e-mail, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.

2. Sharing hardware. In a networked environment, each computer on a network can access and use hardware on the network. Suppose several personal computers on a network each require the use of a laser printer. If the personal computers and a laser printer are connected to a network, each user can then access the laser printer on the network, as they need it.

3. Sharing files, data, and information. In a network environment, any authorized user can access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.

4. Sharing software. Users connected to a network can access application programs on the network.

5. Data protection: You should know by now that it's vital to back up your computer data regularly. A network makes it easier to back up all of your company's data on an offsite server, or other backup systems.

6. Remote access: Having your own network allows greater mobility while maintaining the same level of productivity. With remote access in place, users are able to access the same files, data, and messages even when they're not in the office. This access can even be given to mobile handheld devices.

Types of networks

There are three basic types of networks:

1. LAN (Local Area Network)

2. MAN (Metropolitan Area Network)

3. WAN (Wide Area Network)

Local Area Network:

The Local Area Network is also referred as LAN. This system spans on a small area like a small office or home. The computer systems are linked with cables. In LAN system computers on the same site could be linked. The smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many LANs are divided into logical groups called subnets. An Internet Protocol (IP) "Class A" LAN can in theory accommodate more than 16 million devices organized into subnets.

Advantages

High Speed: Data rates of currently available LANs cover a wide range. The slowest transfer data at around 100 kbps while the fastest have data rates of up to 100 mbps.

Low Cost: Many applications of LANs involve low cost microprocessors systems; it is desirable that connection of such systems to a LAN should be economic..

High reliability/Integrity: Since LAN is s set of multiple interconnected systems; it offers a good backup capability in the event of one or two systems failing in the network. This enhances the reliability and availability of the systems to users.

Installation flexibility: LAN offers flexibility in locating the equipment. Most computers on a LAN are physically placed at the user table, which is most convenient for working and improves productivity significantly.

Expandability: Unlike a large centralized system, a LAN may evolve with time. It may be put into operation with a small investment, and more systems.

East of Access: The connection pattern of a LAN is normally a simple topological form such as a ring or a tree and this has implications for the routing of packets on a LAN.

Metropolitan Area Networks:

The Metropolitan Area Networks connect multiple geographically nearby LANs to one another (over an area of up to a few dozen kilometres) at high speeds. Thus, a MAN lets two remote nodes communicate as if they were part of the same local area network. A MAN is made from switches or routers connected to one another with high-speed links (usually fibre optic cables). MAN is designed to extend over the entire city. It may be a single network as a cable TV network or it may be means of connecting a number of LANs into a larger network so that resources may be shared. MAN is wholly owned and operated by a private company or may be a service provided by a public company



Wide Area Network:

A Wide Area Network or WAN is a type of networking where a number of resources are installed across a large area such as multinational business. Through WAN offices in different countries can be interconnected. The best example of a WAN could be the Internet that is the largest network in the world. In WAN computer systems on different sites can be linked.



Some other types of networks are:

1. WLAN - Wireless Local Area Network

2. SAN - Storage Area Network, System Area Network, Server Area Network, Small Area Network

3. CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network

4. PAN - Personal Area Network



Wireless Local Area Network –

A LAN based on Wi-Fi wireless network technology.


Storage Area Network –

It connects servers to data storage devices through a technology like Fibre Channel. It links high-performance computers with high-speed connections in a cluster configuration


Campus Area Network –

A network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.


Personal Area Network (PAN) –

Personal Area Network is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless connections between devices. The reach of a PAN typically extends to 10 meters.

Type of Computer Virus

computer virus

A computer virus is a program that explicitly copies itself. This may lead to it spreading from machine to machine and is typically done without the user's knowledge or permission. Viruses, by definition, add their code to your system in such a way that when the infected part of the system executes, the virus does also.

About Viruses:
Some viruses display obvious symptoms, and some cause damage to files in a system they have infected. A non-damaging virus is still a virus, not a prank and, other things being equal, viruses without obvious symptoms are more likely to spread further and persist longer than those that rapidly draw attention to themselves.

There are no 'good' viruses, simply because a virus is code that was not intentionally installed by the user. Users must be able to control their computers, and that requires that they have the power to install and remove software; that no software is installed, modified, or removed without their knowledge and permission. A virus is surreptitiously self-installed. It may modify other software in the system without user awareness, and removal can be difficult and costly.

Many viruses cause intentional damage. But many more cause damage that may not have been intended by the virus writer. For instance, when a virus finds itself in a very different environment than that for which it was written, what was intended to be a non-destructive virus can prove very destructive.


Computer Virus is a kind of malicious software written intentionally to enter a computer without the user’s permission or knowledge, with an ability to replicate itself, thus continuing to spread. Some viruses do little but replicate others can cause severe harm or adversely effect program and performance of the system. A virus should never be assumed harmless and left on a system. Most common types of viruses are mentioned below:
Resident Viruses

This type of virus is a permanent which dwells in the RAM memory. From there it can overcome and interrupt all of the operations executed by the system: corrupting files and programs that are opened, closed, copied, renamed etc.

Examples include: Randex, CMJ, Meve, and MrKlunky.

Direct Action Viruses

The main purpose of this virus is to replicate and take action when it is executed. When a specific condition is met, the virus will go into action and infect files in the directory or folder that it is in and in directories that are specified in the AUTOEXEC.BAT file PATH. This batch file is always located in the root directory of the hard disk and carries out certain operations when the computer is booted.


Overwrite Viruses

Virus of this kind is characterized by the fact that it deletes the information contained in the files that it infects, rendering them partially or totally useless once they have been infected.

The only way to clean a file infected by an overwrite virus is to delete the file completely, thus losing the original content.

Examples of this virus include: Way, Trj.Reboot, Trivial.88.D.

Boot Virus

This type of virus affects the boot sector of a floppy or hard disk. This is a crucial part of a disk, in which information on the disk itself is stored together with a program that makes it possible to boot (start) the computer from the disk.
The best way of avoiding boot viruses is to ensure that floppy disks are write-protected and never start your computer with an unknown floppy disk in the disk drive.
Examples of boot viruses include: Polyboot.B, AntiEXE.


Macro Virus

Macro viruses infect files that are created using certain applications or programs that contain macros. These mini-programs make it possible to automate series of operations so that they are performed as a single action, thereby saving the user from having to carry them out one by one.


Examples of macro viruses: Relax, Melissa.A, Bablas, O97M/Y2K.

Directory Virus

Directory viruses change the paths that indicate the location of a file. By executing a program (file with the extension .EXE or .COM) which has been infected by a virus, you are unknowingly running the virus program, while the original file and program have been previously moved by the virus.

Once infected it becomes impossible to locate the original files.


Polymorphic Virus

Polymorphic viruses encrypt or encode themselves in a different way (using different algorithms and encryption keys) every time they infect a system.

This makes it impossible for anti-viruses to find them using string or signature searches (because they are different in each encryption) and also enables them to create a large number of copies of themselves.

Examples include: Elkern, Marburg, Satan Bug, and Tuareg.


File Infectors

This type of virus infects programs or executable files (files with an .EXE or .COM extension). When one of these programs is run, directly or indirectly, the virus is activated, producing the damaging effects it is programmed to carry out. The majority of existing viruses belong to this category, and can be classified depending on the actions that they carry out.


Companion Viruses

Companion viruses can be considered file infector viruses like resident or direct action types. They are known as companion viruses because once they get into the system they "accompany" the other files that already exist. In other words, in order to carry out their infection routines, companion viruses can wait in memory until a program is run (resident viruses) or act immediately by making copies of themselves (direct action viruses).
Some examples include: Stator, Asimov.1539, and Terrax.1069


FAT Virus

The file allocation table or FAT is the part of a disk used to connect information and is a vital part of the normal functioning of the computer.

This type of virus attack can be especially dangerous, by preventing access to certain sections of the disk where important files are stored. Damage caused can result in information losses from individual files or even entire directories.


Worms

A worm is a program very similar to a virus; it has the ability to self-replicate, and can lead to negative effects on your system and most importantly they are detected and eliminated by antiviruses.


Examples of worms include: PSWBugbear.B, Lovgate.F, Trile.C, Sobig.D, Mapson.


Trojans or Trojan Horses

Another unsavory breed of malicious code are Trojans or Trojan horses, which unlike viruses do not reproduce by infecting other files, nor do they self-replicate like worms.
Logic Bombs

They are not considered viruses because they do not replicate. They are not even programs in their own right but rather camouflaged segments of other programs.
Their objective is to destroy data on the computer once certain conditions have been met. Logic bombs go undetected until launched, and the results can be destructive

Advantages of Internet

Communication:
The foremost target of internet has always been the communication. And internet has excelled beyond the expectations .Still innovations are going on to make it faster, more reliable. By the advent of computer’s Internet, our earth has reduced and has attained the form of a global village.
Now we can communicate in a fraction of second with a person who is sitting in the other part of the world. Today for better communication, we can avail the facilities of e-mail; we can chat for hours with our loved ones. There are plenty messenger services in offering. With help of such services, it has become very easy to establish a kind of global friendship where you can share your thoughts, can explore other cultures of different ethnicity.


Information

Information is probably the biggest advantage internet is offering. The Internet is a virtual treasure trove of information. Any kind of information on any topic under the sun is available on the Internet. The search engines like Google, yahoo is at your service on the Internet. You can almost find any type of data on almost any kind of subject that you are looking for. There is a huge amount of information available on the internet for just about every subject known to man, ranging from government law and services, trade fairs and conferences, market information, new ideas and technical support, the list is end less.

Entertainment
Entertainment is another popular reason why many people prefer to surf the Internet. In fact, media of internet has become quite successful in trapping entertainment Sector. Downloading games, visiting chat rooms or just surfing the Web are some of the uses people have discovered. There are numerous games that may be downloaded from the Internet for free. The industry of online gaming has tasted dramatic and phenomenal attention by game lovers. Chat rooms are popular because users can meet new and interesting people. In fact, the Internet has been successfully used by people to find life long partners. When people surf the Web, there are numerous things that can be found. Music, hobbies, news and more can be found and shared on the Internet.

Services
Many services are now provided on the internet such as online banking, job seeking, purchasing tickets for your favorite movies, guidance services on array of topics engulfing the every aspect of life, and hotel reservations.

E-Commerce
Ecommerce is the concept used for any type of commercial, or business deals that involves the transfer of information across the globe via Internet. It has become a phenomenon associated with any kind of shopping, almost anything. You name it and Ecommerce with its giant tentacles engulfing every single product and service will make you available at your door steps.

Disadvantages of Internet

Theft of Personal information
If you use the Internet, you may be facing grave danger as your personal information such as name, address, credit card number etc. can be accessed by culprits.

Spamming
Spamming refers to sending unwanted e-mails in bulk, which provide no purpose and needlessly obstruct the entire system. Such illegal activities can be very frustrating for you, and so instead of just ignoring it, you should make an effort to try and stop these activities so that using the Internet can become that much safer.

Virus threat
Virus is nothing but a program which disrupts the normal functioning of your computer systems. Computers attached to internet are more prone to virus attacks and they can end up into crashing your whole hard disk, causing you considerable headache.


Pornography: This is perhaps the biggest threat related to your children’s healthy mental life. A very serious issue concerning the Internet. There are thousands of pornographic sites on the Internet that can be easily found and can be a detrimental factor to letting children use the Internet.

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite (TCP/IP) to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and optical networking technologies. The Internet carries a vast array of information resources and services, most notably the inter-linked hypertext documents of the World Wide Web (WWW) and the infrastructure to support electronic mail.


The Internet has no centralized governance in either technological implementation or policies for access and usage; each constituent network sets its own standards. Only the overreaching definitions of the two principal name spaces in the Internet, the Internet Protocol address space and the Domain Name System, are directed by a maintainer organization, the Internet Corporation for Assigned Names and Numbers (ICANN). The technical underpinning and standardization of the core protocols (IPv4 and IPv6) is an activity of the Internet Engineering Task Force (IETF), a non-profit organization of loosely affiliated international participants that anyone may associate with by contributing technical expertise.


What is Internet?

The Internet is a massive network of networks, a networking infrastructure. It connects millions of computers together globally, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet. Information that travels over the Internet does so via a variety of languages known as protocols.

What is The Web (World Wide Web)?

The World Wide Web, or simply Web, is a way of accessing information over the medium of the Internet. It is an information-sharing model that is built on top of the Internet. The Web uses the HTTP protocol, only one of the languages spoken over the Internet, to transmit data. Web services, which use HTTP to allow applications to communicate in order to exchange business logic, use the Web to share information. The Web also utilizes browsers, such as Internet Explorer or Firefox, to access Web documents called Web pages that are linked to each other via hyperlinks. Web documents also contain graphics, sounds, text and video.

Internet vs. Web

The terms Internet and World Wide Web are often used in everyday speech without much distinction. However, the Internet and the World Wide Web are not one and the same. The Internet is a global data communications system. It is a hardware and software infrastructure that provides connectivity between computers. In contrast, the Web is one of the services communicated via the Internet. It is a collection of interconnected documents and other resources, linked by hyperlinks and URLs.


The Domain Name System

Domain Name System (DNS) is a database system that translates a computer's fully qualified domain name into an IP address. Networked computers use IP addresses to locate and connect to each other, but IP addresses can be difficult for people to remember. For example, on the web, it's much easier to remember the domain name www.amazon.com than it is to remember its corresponding IP address (207.171.166.48). DNS allows you to connect to another networked computer or remote service by using its user-friendly domain name rather than its numerical IP address.



Education - EDU

Government - GOV

Military - MIL

International - INT

Network - NET

(Non-Profit) Organization - ORG

Commercial – COM


Intranet

An intranet is a private network that is contained within an enterprise. It may consist of many interlinked local area networks and also use leased lines in the wide area network. Typically, an intranet includes connections through one or more gateway computers to the outside Internet. The main purpose of an intranet is to share company information and computing resources among employees. An intranet can also be used to facilitate working in groups and for teleconferences.

Intranets utilize standard network hardware and software technologies like Ethernet, Wi-Fi, TCP/IP, Web browsers and Web servers. An organization's intranet typically includes Internet access but is firewalled so that its computers cannot be reached directly from the outside.



Extranet

An extranet is a private network that uses Internet protocols, network connectivity. An extranet can be viewed as part of a company's intranet that is extended to users outside the company, usually via the Internet.

An extranet uses Internet technology and the public telecommunication system to securely share part of a business's information or operations with suppliers, vendors, partners, customers, or other businesses.



Advantages

• Exchange large volumes of data using Electronic Data Interchange (EDI)

• Share product catalogs exclusively with trade partners

• Collaborate with other companies on joint development efforts

• Jointly develop and use training programs with other companies

• Provide or access services provided by one company to a group of other companies, such as an online banking application managed by one company on behalf of affiliated banks

• Share news of common interest exclusively

Disadvantages

• Extranets can be expensive to implement and maintain within an organization (e.g., hardware, software, employee training costs), if hosted internally rather than by an application service provider.

• Security of extranets can be a concern when hosting valuable or proprietary information.

Application of Internet

1. Blogging: A blog is used as a communication platform to interact with people. The owner of the blog can create the blog about anything of their preference

2. Shopping: Internet can be used for online shopping.

3. Networking: Social networking has created new ways to communicate and share information from all around the world. A social network service creates online communities of people who share interests and/or activities, or who are interested in exploring the interests and activities of others

4. E-Mail: Electronic mail or E-Mail is a electronic way of keeping in touch with someone. E-mails can be read anywhere and sent from anywhere.

5. World Wide Web. The World Wide Web is not a physical place, not a set of files, nor even a network of computers. The heart of the WEB lies in the protocols (common communication rules and languages) that define its use. The WWW uses hypertext transfer protocols (http) to transport files from one place to another.

Main Memory

MEMORY

Internal storage areas in the computer The term memory identifies data storage that comes in the form of chips, and the word storage is used for memory that exists on tapes or disks. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk.
Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. A computer that has 1 megabyte of memory, therefore, can hold about 1 million bytes (or characters) of information.

Memory Manufacturers Kingston, Rambus, Crucial, Samsung, PNY, Micron
Memory Terminology

Memory speed - measured in nanoseconds, this is the time to access data that is stored in memory
the lower the nanoseconds the faster the memory (2ns-80ns)

Parity - A simple error checking method use in memory correction

ECC-Error correction code use in memory correction for newer computers

Memory Banks - A socket where memory is installed Example 4 banks will have 8MB of memory each for a total of 32MB

There are several different types of memory:

240-pin DIMM----------------------------- DDR3 SDRAM

ROM or Read Only Memory, Computers almost always contain a small amount of read-only memory that holds instructions for starting up the computer. Unlike RAM, ROM cannot be written to. It is non-volatile which means once you turn off the computer the information is still there.


PROM, short for programmable read-only memory 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 RAM, PROM's retain their contents when the computer is turned off. The difference between a PROM and a ROM (read-only memory) is that a PROM is manufactured as blank memory, whereas a ROM is programmed during the manufacturing process. To write data onto a PROM chip, you need a special device called a PROM programmer or PROM burner. The process of programming a PROM is sometimes called burning the PROM.

EPROM (erasable programmable read-only memory) is a special type of PROM that can be erased by exposing it to ultraviolet light. Once it is erased, it can be reprogrammed. An EEPROM is similar to a PROM, but requires only electricity to be erased.

EEPROM- Acronym for electrically erasable programmable read-only memory. Pronounced double-ee-prom or e-e-prom, an EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM. EEPROM is similar to flash memory (sometimes called flash EEPROM). 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. This makes flash memory faster.

RAM (Random Access Memory) is a temporary (Volatile) storage area utilized by the CPU. Before a program can be ran the program is loaded into the memory which allows the CPU direct access to the program.




2 Types of RAM

SRAM short for static random access memory and pronounced ess-ram. SRAM is a type of memory that is faster and more reliable than the more common DRAM (dynamic RAM). The term static is derived from the fact that it doesn't need to be refreshed like dynamic RAM.
SRAM is often used only as a memory cache usually found in the CPU (L1, L2 and L3 Cache)

DRAM stands for dynamic random access memory, a type of memory used in most personal computers.

Types of DRAM Packages and DRAM Memory

LAPTOP MEMORY
(72, 144, 200) SO-DIMM

SO-DIMM Short for Small Outline DIMM, a small version of a DIMM used commonly in notebook computers. 72 supports 32bit and 144 and 200 SO-DIMM pins supports a full 64-bit transfer.
(144, 172) Micro-DIMM

Micro-DIMM Short for Micro Dual Inline Memory Module, a competing memory used on laptops, mostly supports 144 and 172 pins.

SIMM Acronym for single in-line memory module, a small circuit board that can hold a group of memory chips. Typically, SIMM's holds up 8 (on Macintoshes) or 9 (on PCs) RAM chips. On PCs, the ninth chip is often used for parity error checking. Unlike memory chips, SIMM's is measured in bytes rather than bits. SIMM's is easier to install than individual memory chips. A SIMM is either 30 or 72 pins.
30 pin SIMM (Usually FPM or EDO RAM)

FPM RAM Short for Fast Page Mode RAM, a type of Dynamic RAM (DRAM) that allows faster access to data in the same row or page. Page-mode memory works by eliminating the need for a row address if data is located in the row previously accessed. It is sometimes called page mode memory.

72 pin SIMM (EDO RAM)

EDO DRAM Short for Extended Data Output Dynamic Random Access Memory, a type of DRAM that is faster than conventional DRAM. Unlike conventional DRAM which can only access one block of data at a time, EDO RAM can start fetching the next block of memory at the same time that it sends the previous block to the CPU.

DIMM Short for dual in-line memory module, a small circuit board that holds memory chips. A single in-line memory module (SIMM) has a 32-bit path to the memory chips whereas a DIMM has 64-bit path. Because the Pentium processor requires a 64-bit path to memory, you need to install SIMM's two at a time. With DIMM's, you can install memory one DIMM at a time. A DIMM contains 168 pins.

168 pin DIMM (SDRAM)
SDRAM Short for Synchronous DRAM, a new type of DRAM that can run at much higher clock speeds than conventional memory. SDRAM actually synchronizes itself with the CPU's bus and is capable of running at 133 MHz, about three times faster than conventional FPM RAM, and about twice as fast EDO DRAM . SDRAM is replacing EDO DRAM in many newer computers
SDRAM delivers data in high speed burst

184 pin DIMM (DDR-SDRAM)

DDR SDRAM Short for Double Data Rate-Synchronous DRAM, a type of SDRAM that supports data transfers on both edges of each clock cycle, effectively doubles the memory chip's data throughput. DDR-SDRAM is also called SDRAM II.

240 DIMM (DDR2-SDRAM)
DDR2-SDRAM Short for Double Data Rate Synchronous DRAM 2 is a type of DDR that supports
higher's speeds than it's predecessor DDR SDRAM

240 DIMM (DDR3-SDRAM)
DDR3-SDRAM Short for Double Data Rate Synchronous DRAM 3 is the newest type of DDR that supports the fastest speed of all the SDRAM memory

184 pin RIMM (RDRAM)

RIMM Rambus Inline Memory Module, The memory module used with RDRAM chips. It is similar to a DIMM package but uses different pin settings. Rambus trademarked the term RIMM as an entire word. It is the term used for a module using Rambus technology. It is sometimes incorrectly used as an acronym for Rambus Inline Memory Module. A RIMM contains 184 or 232pins. Note must use all sockets in RIMM installation or use C_RIMM to terminate banks

232 pin RIMM (RDRAM)
RDRAM Short for Rambus DRAM, a type of memory (DRAM) developed by Rambus, Inc.
In 1997, Intel announced that it would license the Rambus technology for use on its future motherboards, thus making it the likely de facto standard for memory architectures.
SIMM and DIMM Sockets


SDRAM Chart
168 DIMM (SDRAM)

Module Standard Module Format Chip Type Clock Speed
(MHz) Cycles Per clock Bus Speed Bus Width
(Bytes) Transfer Rate
(MB/s)
PC66 SDR DIMM 10ns 66 1 66 8 533
PC100 SDR DIMM 8ns 100 1 100 8 800
PC133 SDR DIMM 7ns 133 1 133 8 1,066

DDR SDRAM Chart
184 DIMM (DDR-SDRAM)

Module Standard Module Format Chip Type Clock Speed
(MHz) Cycles Per clock Bus Speed Bus Width
(Bytes) Transfer Rate
(MB/s)
PC1600 DDR DIMM DDR200 100 2 200 8 1,600
PC2100 DDR DIMM DDR266 133 2 266 8 2.133
PC2400 DDR DIMM DDR300 150 2 300 8 2,400
PC2700 DDR DIMM DDR333 166 2 333 8 2,667
PC3000 DDR DIMM DDR366 183 2 366 8 2,933
PC3200 DDR DIMM DDR400 200 2 400 8 3,200
PC3500 DDR DIMM DDR433 216 2 433 8 3,466
PC3700 DDR DIMM DDR466 233 2 466 8 3,733
PC4000 DDR DIMM DDR500 250 2 500 8 4,000
PC4300 DDR DIMM DDR533 266 2 533 8 4,266

DDR2 SDRAM Chart

240 DIMM (DDR2-SDRAM)
Module Standard Module Format Chip Type Clock Speed
(MHz) Cycles Per clock Bus Speed Bus Width
(Bytes) Transfer Rate
(MB/s)
PC2-3200 DDR2 DIMM DDR2-400 200 2 400 8 3,200
PC2-4300 DDR2 DIMM DDR2-533 266 2 533 8 4,266
PC2-5400 DDR2 DIMM DDR2-667 333 2 667 8 5,333
PC2-6400 DDR2 DIMM DDR2-800 400 2 800 8 6,400

240 DIMM (DDR3-SDRAM)

Module Standard Module Format Chip Type Clock Speed
(MHz) Cycles Per clock Bus Speed Bus Width
(Bytes) Transfer Rate
(MB/s)
PC3-6400 DDR3
DIMM DDR3-800 400 2 800 8 6,400
PC3-8500 DDR3
DIMM DDR3-1066 533 2 1,066 8 8,500
PC3-10600 DDR3
DIMM DDR3-1333 667 2 1,334 8 10,670
PC3-12800 DDR3
DIMM DDR3-1600 800 2 1,600 8 12,800

RDRAM Chart

232 RIMM (RDRAM)
Module Standard Module Format Chip Type Clock Speed
(MHz) Cycles Per clock Bus Speed Bus Width
(Bytes) Transfer Rate
(MB/s)
RIMM 1200 RIMM-16 PC600 300 2 600 2 1,200
RIMM 1400 RIMM-16 PC700 350 2 700 2 1,400
RIMM 1600 RIMM-16 PC800 400 2 800 2 1,600
RIMM 2100 RIMM-16 PC1066 533 2 1,066 2 2,133
RIMM 2400 RIMM-16 PC1200 600 2 1,200 2 2,400
RIMM 3200 RIMM-32 PC800 400 2 800 2 3,200
RIMM 4200 RIMM-32 PC1066 533 2 1,066 2 4,266
RIMM 4800 RIMM-32 PC1200 600 2 1,200 2 4,800
RAM Desktop Installation

Note RAM Memory Sticks come in the following sizes
8MB, 16MB, 32MB, 64MB, 128MB, 256MB, 512MB, 1GB, 2GB, 4GB and 8GB

SIMM – Single Inline Memory Module Installation (30 or 72 pin)

1. Place SIMM in a 45 degree angle, push it upright to lock with the corresponding notch on the sides
2. Must be installed in same pairs
3. Must populate first two slots of the SIMM sockets in order for it to work

DIMM – Dual Inline Memory Module Installation (168, 184 or 240 pin)
1. The first thing you do is open the plastic retaining clips on each side of slots you are going to use.
2. Align the cut-out on the module pin connector with the engaging pin on the slot
3. Holding the module upright press down both ends.
4. When the module is correctly seated, retaining clips should lock automatically.
5. DIMM’s can be installed as a single pair (unless it states Dual Channel then you must install it in pairs)

RIMM – Rambus Inline Memory Module Installation (184 or 232 pin)

1. The first thing you do is open the plastic retaining clips on each side of slots you are going to use.
2. Align the cut-out on the module pin connector with the engaging pin on the slot
3. Holding the module upright press down both ends.
4. When the module is correctly seated, retaining clips should lock automatically.
5. Must populate all RIMM slots available
3. If not unpopulated slots must use CRIMM’s (Continuity Rambus Inline Memory Module)

Memory Troubleshooting

MEMORY (when installing use a ground strap because of ESD)
ESD (low and high humidity)
Mixed Memory usually equals fried memory
Parity Errors or ECC Errors (Memory correction errors)
SIMMS must be installed in pairs
RIMMS must be all installed in all slots or CRIMM's must be needed in unvacated RIMM slots
General Protection Fault (memory overwrite)
Not enough memory (computer is slow)
NMI -Non Maskable Interrupt will cause BSOD (Blue Screen of Death)
Multiple beeps when booting up check that memory is properly installed and working
No Video (Reseat memory)
Memory speeds set in BIOS/CMOS Setup
Virtual Memory (Page fault)
Chip Creep - Thermal expansion and contraction

Introduction to Database

Database
A database is a structured collection of related data. A database helps us to keep the information in a organized way so that it can easily be accessed, managed, and updated.

Data – a collection of raw facts made up of text, numbers and dates.

Murray 35000 7/18/86

Information - the meaning given to data in a way so that it can be understood and interpreted.

Mr. Rohit is a sales person whose annual salary is 35, 0000 and whose hire date is July 18, 2009

Databases can be analyzed at different levels ,also known as Data Abstraction which means  hiding the complexities:

• View Level
• Logical /Conceptual Level
• Physical Level

View level: Application programs hide details of data types. Views can also hide information (e.g., salary) for security purposes.

Logical level: Describes what data is stored in database, and the relationships among the data

Physical level: Describes how a record (e.g., customer) is stored.

.

Type customer = record
Name: string;
Street: string;
City: integer;
End;

Data Models
A data model is a collection of tools for describing Data, Data relationships, Data semantics, and Data constraints.

Type of Data Model

1. Entity-Relationship Model
2. Relational Model
3. Other Models:
• Object-Oriented Model
• Older models: Network Model and Hierarchical Model

1. Entity-Relationship Model

• Entity: Entity is a Real-world object distinguishable from other objects.
• Relationship: Relationship is the association among two or more entities.

E-R model describes the real world Entities (objects) (E.g. customers, accounts, bank branch) and the Relationships between these entities. The entity-relationship model (or ER model) is a way of graphically representing the logical relationships between entities (or objects).


Components of E-R model:

• Rectangles representing entity sets.
• Ellipses representing attributes.
• Diamonds representing relationship sets.
• Lines links attributes to entity sets and entity sets to relationship sets.

Example of E-R Model:

2. Relational Model

The relational model used the basic concept of a relation or table. The columns or fields in the table identify the attributes such as name, age, and so. A tuple or row contains all the data of a single instance of the table. In the relational model, every tuple must have a unique identification or key based on the data.

Hierarchical Model

The Hierarchical Database Model defines hierarchically-arranged data. Relationships in such a system are thought of in terms of children and parents such that a child may only have one parent but a parent can have multiple children. Parents and children are tied together by links called "pointers" (perhaps physical addresses inside the file system). A parent will have a list of pointers to each of their children.


Network Model

The network model is very similar to the hierarchical model actually. In fact, the hierarchical model is a subset of the network model. However, instead of using a single-parent tree hierarchy, the network model uses set theory to provide a tree-like hierarchy with the exception that child tables were allowed to have more than one parent. This allowed the network model to support many-to-many relationships.

Computer Hardware

The hardware of computer is divided into three broad categories:

1. Processor/Processing Unit
2. Memory(Internal & External)
3. I/O (input/output).

Processor

The processor is the part of the computer that actually does the computations. This is sometimes called an MPU (Main Processor Unit) or CPU (Central Processing Unit or Central Processor Unit).
A processor typically contains an Arithmetic & Logic unit (ALU), Control Unit (CU).

Arithmetic & Logic Unit (ALU)

An arithmetic & logic unit (ALU) performs integer arithmetic and logic operations. It also performs shift and rotate operations and other specialized operations. Usually floating point arithmetic is performed by a dedicated Floating Point Unit (FPU), which may be implemented as a co-processor.

Control Unit (CU)

Control units are in charge of the computer. Control units fetch and decode machine instructions. Control units may also control some external devices.

Main Storage

Main storage is also called memory or internal memory (to distinguish from external memory, such as hard drives).

RAM is Random Access Memory, and is the basic kind of internal memory. RAM is called “random access” because the processor or computer can access any location in memory (as contrasted with sequential access devices, which must be accessed in order). RAM has been made from transistors, integrated circuits, magnetic core, or anything that can hold and store binary values (one/zero, plus/minus, open/close, positive/negative, high/low, etc.).

Static RAM is called static because it will continue to hold and store information even when power is removed. Magnetic cores are examples of static memory.
Dynamic RAM is called dynamic because it loses all data when power is removed. Transistors and integrated circuits are examples of dynamic memory.

ROM is Read Only Memory (it is also random access, but only for read). ROM is typically used to store things that will never change for the life of the computer, such as low level portions of an operating system.

Cache (pronounced cash) Memory :
Cache (pronounced cash) memory is extremely fast memory that is built into a computer’s central processing unit (CPU), or located next to it on a separate chip. The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage of cache memory is that the CPU does not have to use the motherboard’s system bus for data transfer. Whenever data must be passed through the system bus, the data transfer speed slows to the motherboard’s capability. The CPU can process data much faster by avoiding the bottleneck created by the system bus.

Cache built into the CPU itself is referred to as Level 1 (L1) cache. Cache that resides on a separate chip next to the CPU is called Level 2 (L2) cache. Some CPUs have both L1 and L2 cache built-in and designate the separate cache chip as Level 3 (L3) cache.


Data storage device

Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers A data storage device is a device for recording (storing) information (data).

Primary Storage

• It is directly accessable by CPU
• It is volatile in nature
• All instruction are stored in primary memory before it can be uesd for processing
• It is fastes among all type of memory
• It has small storage space

Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required.

Secondary Storage

• It non-volatile ,that is, data remain stored even when the computer is switched off.
• It is slower than primary memory
• It has large storage space

Secondary storage (or external memory) differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. In modern computers, hard disk drives are usually used as secondary storage.

Tertiary Storage

• It is slower than secondary memory
• Generally used to store large amount of data
• It needs robotics mechanism to insert and remove
• Used in supercomputer as accessing data is slow from Tertiary Storage Device

Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use. It is primarily used for archival of rarely accessed information since it is much slower than secondary storage. This is primarily useful for extraordinarily large data stores, accessed without human operators.

Off-line storage

• Pen drive is an example of off-line storage device
• It reqiures human operater to insert and remove
• It is portable and can be carried with ease

Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit.The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.

Input

Input devices are devices that bring information into a computer. Information and commands are issued to the computer by way of input devices. Input device is used to insert data and instructions for processing in the computer.
Examples of input devices include the keyboard, mouse, modem, joystick, digitizing pen and tablet, microphone, touch screens, scanner, camera.

Output

Output devices are devices that bring information out of a computer and present data in a form that people can understand.
Examples of output devices include monitors, printers, and pen plotters.

Types of Computer

Types of Computer

Since the invention of computers from first generation and fourth generation computers, they have been classified according to their types and how they operate that is input, process and output information.
Computer types can be divided into 3 categories according to electronic nature. Types of computers are classified according to how a particular Computer functions.

The types of computer are

• Analog Computers
• Digital Computers
• Hybrid Computers
Analog Computers
• It uses discontinuous analog signal
• Used in Scientifics research
• It is programmed to perform arithmetic and logical operations

Analog types of Computer uses what is known as analog signals that are represented by a continuous set of varying voltages and are used in scientific research centers, and hospitals.
With analog types of computer values are represented by physical measurable quantities e.g. voltages. Analog computer types program arithmetic and logical operations by measuring physical changes i.e. temperatures or pressure.

Digital Computer
• Have two state 0 and 1(On and Off)
• It works on high speed discrete signal of (0 or 1)

With these types of computers operation are on electrical input that can attain two inputs states of ON=1 and state of OFF = 0. With digital type of computers data is represented by digit of 0 and 1 or off state and on state. Digital computer type recognizes data by counting discrete signal of (0 or 1) they are high speed programmable; they compute values and stores results.

The Digital Computer is divided into Four Categories
1. Microcomputers
2. Minicomputers
3. Mainframes
4. Supercomputers

Microcomputers
• Microcomputer is known as Personal Computer or PC in short
• First introduced by IBM
• It was called micro as CPU was created on a single chip called ‘microprocessors.’

The microcomputer is also known as the "Personal Computer". IBM introduced and marketed
the first widely available, commercialized microcomputer named the “IBM PC” where PC stood for Personal Computer. IBM PC became the standard against which all microcomputers were compared and developed, the “PC” helped provide a name for the industry to grow.
The category is termed “micro” because the fundamental component that allowed the categories development was the CPU created on a single chip .The lower costs helped in the development and production of the CPU and various components of the microcomputer allowed microcomputers to become a broad market general purpose computer.
The general appeal or focus of microcomputers on the individual’s enjoyment and productivity has been a key factor in the microcomputer developments and enhancements over the years.

Microcomputers can be grouped into five smaller groups

1. Workstation
2. Desktop
3. Server
4. Laptop and
5. Notebook.
Each referring to the physical usage of the machines and not necessarily the power.

Workstation generally refers to machines used for intensive calculations on designs such as architecture and buildings.
Desktop generally refer to machines used by business people for word processing, spread sheeting etc, and are physically placed onto a desk.
Server: A computer, or a software package, that provides a specific kind of service to client software running on other computers. The term can refer to a particular piece of software, such as a WWW server, or to the machine on which the software is running.
The Laptop and the notebook are portable machines. Laptops generally are bigger and clumsier due to the power supply being encased in the box holding the CPU.
The Notebook is generally smaller. Notebooks and laptops can work on batteries allowing the user to work with it in aeroplanes, in the car and places computers are not generally available.

Minicomputers
• Access to more Storage space
• Used to access large amount of data simultaneously
• Mainly used in medium size organization
Faster than the microcomputer with access to more storage space and more input and output devices, the minicomputer is used when large groups need access to data simultaneously. The minicomputer can do this because the hardware is designed for plugging in more devices, and the C.P.U. and support chips are designed more for this kind of work than the microcomputers.
Minicomputers are used by medium sized business and small sites of large organizations. They are also used in factories to control automated assembly lines.

Mainframes
• Have more powerful processor
• Used in large organization
• Capable of processing large amount of data simultaneously
Mainframes have more access to storage space and to input/output devices. To work with these extra devices mainframes also have more powerful 'processors'. This power is useful and required by large corporations who have large amounts of data to Process.

Supercomputers
• Supercomputers have multiple CPU and Processor.
• Mainly used for research and Weather Forecast, natural speech recognition

Supercomputers have been developed from the processing requirements of advanced research projects by engineers, scientists and more recently by other research fields. The Supercomputer is a title generally given to computers with processing power well exceeding those of the fastest mainframes and its focus is processing data and manipulation of the data. A significant difference between mainframes and supercomputers is the primary focus of super computers on processing capabilities independent of the many varied input/output devices expected on mainframes.
The major cause for the development of super-class computers has been the continuing Need in the scientific community for faster and faster calculations. Scientists working on atomic physics, computer intensive calculations such as natural speech recognition continue to require more and more computational speed to test their theorems.

Hybrid Computer
• Combination of both analog and digital computer
• It is used to convert the signal from analog to digital and digital to analog

Hybrid computer types are very unique, in the sense that they combined both analog and digital features and operations. Hybrid computers operate by using digital to analog converter and analog to digital converter. By linking the two types of computer above you come up with this new computer type called Hybrid computer.

2. Computer Hardware-CPU, I/O Devices, Storage Devices, Memory

The hardware of computer is divided into three broad categories:

1. Processor/Processing Unit
2. Memory
3. I/O (input/output).

Processor
The processor is the part of the computer that actually does the computations. This is sometimes called an MPU (Main Processor Unit) or CPU (Central Processing Unit or Central Processor Unit).
A processor typically contains an Arithmetic & Logic unit (ALU), Control Unit (CU).

Arithmetic & Logic Unit (ALU)
An arithmetic & logic unit (ALU) performs integer arithmetic and logic operations. It also performs shift and rotate operations and other specialized operations. Usually floating point arithmetic is performed by a dedicated Floating Point Unit (FPU), which may be implemented as a co-processor.

Control Unit (CU)
Control units are in charge of the computer. Control units fetch and decode machine instructions. Control units may also control some external devices.

Main Storage
Main storage is also called memory or internal memory (to distinguish from external memory, such as hard drives).

RAM is Random Access Memory, and is the basic kind of internal memory. RAM is called “random access” because the processor or computer can access any location in memory (as contrasted with sequential access devices, which must be accessed in order). RAM has been made from transistors, integrated circuits, magnetic core, or anything that can hold and store binary values (one/zero, plus/minus, open/close, positive/negative, high/low, etc.).

Static RAM is called static because it will continue to hold and store information even when power is removed. Magnetic cores are examples of static memory.
Dynamic RAM is called dynamic because it loses all data when power is removed. Transistors and integrated circuits are examples of dynamic memory.

ROM is Read Only Memory (it is also random access, but only for read). ROM is typically used to store things that will never change for the life of the computer, such as low level portions of an operating system.



Data storage device
Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer, that of information retention. It is one of the fundamental components of all modern computers A data storage device is a device for recording (storing) information (data).

Primary Storage
• It is directly accessable by CPU
• It is volatile in nature
• All instruction are stored in primary memory before it can be uesd for processing
• It is fastes among all type of memory
• It has small storage space

Primary storage (or main memory or internal memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required.

Secondary Storage
• It non-volatile ,that is, data remain stored even when the computer is switched off.
• It is slower than primary memory
• It has large storage space
Secondary storage (or external memory) differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfers the desired data using intermediate area in primary storage. Secondary storage does not lose the data when the device is powered down—it is non-volatile. In modern computers, hard disk drives are usually used as secondary storage.

Tertiary Storage
• It is slower than secondary memory
• Generally used to store large amount of data
• It needs robotics mechanism to insert and remove
• Used in supercomputer as accessing data is slow from Tertiary Storage Device

Tertiary storage or tertiary memory, provides a third level of storage. Typically it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; this data is often copied to secondary storage before use. It is primarily used for archival of rarely accessed information since it is much slower than secondary storage. This is primarily useful for extraordinarily large data stores, accessed without human operators.

Off-line storage
• Pen drive is an example of off-line storage device
• It reqiures human operater to insert and remove
• It is portable and can be carried with ease

Off-line storage is a computer data storage on a medium or a device that is not under the control of a processing unit.The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.




Input
Input devices are devices that bring information into a computer. Information and commands are issued to the computer by way of input devices. Input device is used to insert data and instructions for processing in the computer.
Examples of input devices include the keyboard, mouse, modem, joystick, digitizing pen and tablet, microphone, touch screens, scanner, camera.

Output
Output devices are devices that bring information out of a computer and present data in a form that people can understand.
Examples of output devices include monitors, printers, and pen plotters.

Management Information System

An 'MIS' is a planned system of the collecting, processing, storing and disseminating data in the form of information needed to carry out the functions of management. In a way it is a documented report of the activities that were planned and executed. According to Philip Kotler "A marketing information system consists of people, equipment, and procedures to gather, sort, analyze, evaluate, and distribute needed, timely, and accurate information to marketing decision makers."
A Management Information System (MIS) is a system or process that provides information needed to manage organizations effectively . Management information systems cover the application of people, documents, technologies, and procedures used by management to solve business problems such as costing a product, service or a business-wide strategy. Management information systems are distinct from regular information systems in that they are used to analyze other information systems applied in operational activities in the organization. Academically, the term is commonly used to refer to the group of information management methods tied to the automation or support of human decision making, e.g. Decision Support Systems, Expert systems, and Executive information systems.

Management is usually defined as planning, organizing, directing, and controlling the business operation. Management is the process of allocating an organization's inputs, including human and economic resources, by planning, organizing, directing, and controlling for the purpose of producing goods or services desired by customers so that organizational objectives are accomplished. If management has knowledge of the planning, organizing, directing, and controlling of the business, its decisions can be made on the basis of facts, and decisions are more accurate and timely.

Information is what is used in the act of informing or the state of being informed. Information includes knowledge acquired by some means. When information is entered into and stored in a computer, it is generally referred to as data. After processing (such as formatting and printing), output data can again be perceived as information. When information is packaged or used for understanding or doing something, it is known as knowledge.

A system is a combination or arrangement of parts to form an integrated whole. A system includes an orderly arrangement according to some common principles or rules. A system is a plan or method of doing something.