TECHNOLOGY

LANs, WANs, and Other Area Networks

Computer networks come in many different shapes and sizes. Over the years, the networking industry has coined terms like "LAN" and "WAN" attempting to define sensible categories for the major types of network designs. The precise meaning of this terminology remains lost on the average person, however.

Area Networks

For historical reasons, the industry refers to nearly every type of network as an "area network." The most commonly-discussed categories of computer networks include the following -

• LAN - Local Area Network
• WAN - Wide Area Network
• MAN - Metropolitan Area Network
• SAN - Storage Area Network
• SAN - System Area Network
• SAN - Server Area Network
• SAN - Small Area Network
• PAN - Personal Area Network
• DAN - Desk Area Network
• CAN - Controller Area Network
• CAN - Cluster Area Network

LANs and WANs were the original flavors of network design. The concept of "area" made good sense at this time, because a key distinction between a LAN and a WAN involves the physical distance that the network spans. A third category, the MAN, also fit into this scheme as it too is centered on a distance-based concept.
As technology improved, new types of networks appeared on the scene. These, too, became known as various types of "area networks" for consistency's sake, although distance no longer proved a useful differentiator.

LAN Basics

A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs, and occasionally a LAN will span a group of nearby buildings. In IP networking, one can conceive of a LAN as a single IP subnet (though this is not necessarily true in practice).

Besides operating in a limited space, LANs include several other distinctive features. LANs are typically owned, controlled, and managed by a single person or organization. They also use certain specific connectivity technologies, primarily Ethernet and Token Ring.




WAN Basics

As the term implies, a wide-area network spans a large physical distance. A WAN like the Internet spans most of the world! A WAN is a geographically-dispered collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. WANs differ from LANs in several important ways. Like the Internet, most WANs are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs use technology like ATM, Frame Relay and X.25 for connectivity.
LANs and WANs at Home

Home networkers with cable modem or DSL service already have encountered LANs and WANs in practice, though they may not have noticed. A cable/DSL router like those in the Linksys family join the home LAN to the WAN link maintained by one's ISP. The ISP provides a WAN IP address used by the router, and all of the computers on the home network use private LAN addresses. On a home network, like many LANs, all computers can communicate directly with each other, but they must go through a central gateway location to reach devices outside of their local area.






What About MAN, SAN, PAN, DAN, and CAN?

Future articles will describe the many other types of area networks in more detail. After LANs and WANs, one will most commonly encounter the following three network designs:

A Metropolitan Area Network connects an area larger than a LAN but smaller than a WAN, such as a city, with dedicated or high-performance hardware.

A Storage Area Network connects servers to data storage devices through a technology like Fibre Channel.

A System Area Network connects high-performance computers with high-speed connections in a cluster configuration.




Conclusion

To the uninitiated, LANs, WANs, and the other area network acroymns appear to be just more alphabet soup in a technology industry already drowning in terminology. The names of these networks are not nearly as important as the technologies used to construct them, however. A person can use the categorizations as a learning tool to better understand concepts like subnets, gateways, and routers.

Simplex, Full-Duplex and Half-Duplex Operation

Another aspect of performance that is worthy of some attention is the mode of operation of the network or connection. Obviously, whenever we connect together device A and device B, there must be some way for A to send to B and B to send to A. Many people don’t realize, however, that networking technologies can differ in terms of how these two directions of communication are handled. Depending on how the network is set up, and the characteristics of the technologies used, performance may be improved through the selection of performance-enhancing modes.

Basic Communication Modes of Operation

Let's begin with a look at the three basic modes of operation that can exist for any network connection, communications channel, or interface.

Simplex Operation

In simplex operation, a network cable or communications channel can only send information in one direction; it's a “one-way street”. This may seem counter-intuitive: what's the point of communications that only travel in one direction? In fact, there are at least two different places where simplex operation is encountered in modern networking.

The first is when two distinct channels are used for communication: one transmits from A to B and the other from B to A. This is surprisingly common, even though not always obvious. For example, most if not all fiber optic communication is simplex, using one strand to send data in each direction. But this may not be obvious if the pair of fiber strands are combined into one cable.

Simplex operation is also used in special types of technologies, especially ones that are asymmetric. For example, one type of satellite Internet access sends data over the satellite only for downloads, while a regular dial-up modem is used for upload to the service provider. In this case, both the satellite link and the dial-up connection are operating in a simplex mode.

Half-Duplex Operation

Technologies that employ half-duplex operation are capable of sending information in both directions between two nodes, but only one direction or the other can be utilized at a time. This is a fairly common mode of operation when there is only a single network medium (cable, radio frequency and so forth) between devices.
While this term is often used to describe the behavior of a pair of devices, it can more generally refer to any number of connected devices that take turns transmitting. For example, in conventional Ethernet networks, any device can transmit, but only one may do so at a time. For this reason, regular (unswitched) Ethernet networks are often said to be “half-duplex”, even though it may seem strange to describe a LAN that way.

Full-Duplex Operation

In full-duplex operation, a connection between two devices is capable of sending data in both directions simultaneously. Full-duplex channels can be constructed either as a pair of simplex links (as described above) or using one channel designed to permit bidirectional simultaneous transmissions. A full-duplex link can only connect two devices, so many such links are required if multiple devices are to be connected together.

Note that the term “full-duplex” is somewhat redundant; “duplex” would suffice, but everyone still says “full-duplex” (likely, to differentiate this mode from half-duplex).

WHAT IS IP ADDRESS? EXPLAIN HOW YOU WILL GET IP ADDRESS OF A COMPUTER SYSTEM?

Definition of IP address

(Internet Protocol address) The address of a device attached to an IP network (TCP/IP network). Every client, server and network device must have a unique IP address for each network connection (network interface). Every IP packet contains a source IP address and a destination IP address.

Static and Dynamic IP

An IP network is somewhat similar to the telephone network in that you have to have the phone number to reach a destination. The big difference is that IP addresses are often temporary.

Each device in an IP network is either assigned a permanent address (static IP) by the network administrator or is assigned a temporary address (dynamic IP) via DHCP software. Routers, firewalls and proxy servers use static addresses as do most servers and printers that serve multiple users. Client machines may use static or dynamic IP addresses. The IP address assigned to your service by your cable or DSL Internet provider is typically dynamic IP. In routers and operating systems, the default configuration for clients is dynamic IP (see DHCP).

Dotted Decimals

IP addresses are written in "dotted decimal" notation, which is four sets of numbers separated by periods; for example, 204.171.64.2. If you knew the IP address of a Web site, you could enter the dotted decimal number into your browser instead of the domain name (which is why we have DNS!).

Although the next version of the IP protocol offers a virtually unlimited number of unique addresses (see IPv6), the traditional IP address (IPv4) uses a 32-bit number that defines both the network and the host computer. The network class determines how many of the 32 bits are used for the network address, leaving the remaining bits for use as the host number (note the numbers of networks and hosts in the table below). The host number can be further divided between subnetworks and hosts (see subnet mask).


Class A, B and C

Although the computer identifies the class by the first three bits of the address (A=0; B=10; C=110), people identify the class by the first number in the address (see range below). This class-based system has also been greatly expanded, eliminating the huge disparity in the number of hosts that each class can accommodate (see CIDR).

Maximum Maximum Number of
Class Number Hosts Bits used in
Number of per Network/Host
Class Range Networks Network ID ID
A 1-126 127 16,777,214 7/24
B 128-191 16,383 65,534 14/16
C 192-223 2,097,151 254 21/8

127 reserved for loopback test






IP - Logical or Physical?

An IP address is somewhat of a hybrid, which can be thought of as either logical or physical, depending on how you view it. It is a unique number assigned to a node, which makes it seem physical, especially because there is so much name-to-IP address resolution going on in the network.

There is also the Ethernet address, which is built into the network adapter. That is indeed physical, and it does not change, which is very typical of physical device names. However, since IP addresses can be dynamically assigned, causing the same client workstation to have a different IP address every day, the IP address seems more like a logical address. Regardless of what it is, it would make a great debate in a computer science class. See logical vs. physical, IPv6, private IP addresses, TCP/IP abc's and IP on Everything.









How do I get an IP address for my computer or server.

There are three ways to get IP addresses for your workstations or servers. One is automatic and the other two require human intervention and registration. We obviously prefer that you obtain an IP address automatically. That way you can take a new computer out of the box, put it together, plug it into the network, and start using it immediately.
The three methods are:

Method Comments Obtained

DHCP Dynamic Host Configuration Protocol Automatically

M-DHCP Requires Application for Manual DHCP Hybrid

BOOTP Required Application for BOOTP Hybrid

Static Requires Application for manual or static Manually


If you can use normal DHCP, please do so. Your computer name gets automatically registered in DNS and it requires no manual actions on anyone's part. If you feel that you have special addressing needs, please read on. Then, if you still feel you have special addressing needs, you may apply for an address by calling Mark Harsen or by opening a Special Address Technical Support case with Networking which is described in the "How do I get one" section on this page.

DHCP - Dynamic Host Configuration Protocol

DHCP was created to meet the needs of the ever-evolving and changing needs of work stations and servers on the network. It was becoming unruly and impossible for network personnel to manually administer the thousands or tens of thousands of computers and addresses for an organization.

DHCP was invented to alleviate this problem. Basically, most computers are already configured, out of the box, to use DHCP. Therefore, you simply take your new computer out of the box, put it together, plug it into the network, and it starts working. Every computer has a name which can be changed by the owner of that machine. The configured name is sent as part of the DHCP request and, if not already taken, that name becomes the name or DNS name for your computer. If the name is taken, the system automatically adds a string to the end of the name to make it unique.

Many people think they need a special address that never changes for their web server, their file server, a Polycom video conferencing unit, or some other specific project. While there are some cases where special addressing needs do exist, the above mentioned are not among them. As long a computer system is online at least once a week, it's IP address will not change. If the IP address does change for a system, the DNS name will be kept up to date and point to the new IP address.




Therefore, everything that uses DNS, which is almost every Internet application, need not obtain an IP address through any other method other than our standard DHCP. This also leaves the users or system administrators free to move their machines around at will. Different networks, and thus different IP addresses, are used around campus and between campuses. Users must reapply for manual or hybrid addresses if the systems are moved to a different VLAN. Using standard DHCP, machines may be moved around campus or across campuses to Springfield, West Plains, Mt. Grove, or even Lebanon without any special actions having to be taken.
Also, if anything on the network changes, users automatically and transparently receive the new information. The machines run without interruption and without the knowledge that some networking stuff behind the walls changed. Other forms of addressing are not so fortunate.

What about Manual or Reserved DHCP addresses?

M-DHCP, Manual DHCP and a "DHCP Reservation" are different names for the same thing. Rarely, a special need exists where it is imperative that an IP address change as little as possible or where multiple DNS names must be associated with the same server. A web server hosting many home pages through different DNS names is a classical example of this. To accomplish this, nothing changes on the users machine. It is left configured to use DHCP, but specific information about the machine is given to Networking that we use to configure our DHCP servers. They will always give out the same address and have the same DNS aliases associated with the address.

If the user moves the machine, however, Networking must be contacted ahead of time to facilitate the move. It's a rather simple process, but failure to do it could result in loss of service to the moved resource.

BOOTP - Bootstrap Protocol

BOOTP was actually the predecessor of DHCP and DHCP is built on the foundation of BOOTP. It is a much older and bulkier attempt to solve the massive addressing problems presented by the Internet Protocol (IP). Users are strongly encouraged to steer clear of BOOTP in favor of DHCP or at least a Manual DHCP address. However, there are still some old systems on the network that do not support any from of DHCP. For those systems, we recommend BOOTP where it is supported. The only systems known to exist that need BOOTP are some cash registers, old Windows 3.11 machines, and old Macintoshes running MAC/TCP. Our recommendation would be to upgrade these machine where possible for these and other reasons.

BOOTP sends a specific request to a central server and expects networking configuration information to be sent to the machine. It configures itself, and attaches properly to the network. Registering a machine to use BOOTP is almost exactly the same as with M-DHCP, but the host name is fixed and can only be changed by Networking at the request of the owner. It is less reliable than DHCP, but shares the advantage that behind the scenes changes are maintained by Networking and the user never need to be concerned by network addressing or topology changes. If the user moves the machine to another VLAN, it must be re-registered.

Statically or Manually Configured

We like this form of addressing least of all. It requires registration of the address and it requires that the all network information, not just the station's IP address, be manually or "hard-coded" into the software on the machine. If the machine moves or if something behind the scenes change, it is most likely that any machine that has a static address will quit working.

We most often get requests from owners of Linux, Sun OS, or other variants of the Unix operating system for static addresses. It is true that most versions of Unix cannot support anything other than static addresses. We hope the Unix industry will someday recognize this flaw and reform as indeed many vendors of Linux already have.

Switching technology

In the next three subsections, we present the three switching techniques used in networks: circuit switching, datagram packet switching and virtual circuit packet switching.

Circuit switching




Circuit switching is the transmission technology that has been used since the first communication networks in the nineteenth century. In circuit switching, a caller must first establish a connection to a callee before any communication is possible. During the connection establishment, resources are allocated between the caller and the callee. Generally, resources are frequency intervals in a Frequency Division Multiplexing (FDM) scheme or more recently time slots in a Time Division Multiplexing (TDM) scheme. The set of resources allocated for a connection is called a circuit, as depicted in Figure 1.1. A path is a sequence of links located between nodes called switches. The path taken by data between its source and destination is determined by the circuit on which it is flowing, and does not change during the lifetime of the connection. The circuit is terminated when the connection is closed.
In circuit switching, resources remain allocated during the full length of a communication, after a circuit is established and until the circuit is terminated and the allocated resources are freed. Resources remain allocated even if no data is flowing on a circuit, hereby wasting link capacity when a circuit does not carry as much traffic as the allocation permits. This is a major issue since frequencies (in FDM) or time slots (in TDM) are available in finite quantity on each link, and establishing a circuit consumes one of these frequencies or slots on each link of the circuit. As a result, establishing circuits for communications that carry less traffic than allocation permits can lead to resource exhaustion and network saturation, preventing further connections from being established. If no circuit can be established between a sender and a receiver because of a lack of resources, the connection is blocked.

A second characteristic of circuit switching is the time cost involved when establishing a connection. In a communication network, circuit-switched or not, nodes need to lookup in a forwarding table to determine on which link to send incoming data, and to actually send data from the input link to the output link. Performing a lookup in a forwarding table and sending the data on an incoming link is called forwarding. Building the forwarding tables is called routing. In circuit switching, routing must be performed for each communication, at circuit establishment time. During circuit establishment, the set of switches and links on the path between the sender and the receiver is determined and messages are exchanged on all the links between the two end hosts of the communication in order to make the resource allocation and build the routing tables. In circuit switching, forwarding tables are hardwired or implemented using fast hardware, making data forwarding at each switch almost instantaneous. Therefore, circuit switching is well suited for long-lasting connections where the initial circuit establishment time cost is balanced by the low forwarding time cost.

The circuit identifier (a range of frequencies in FDM or a time slot position in a TDM frame) is changed by each switch at forwarding time so that switches do not need to have a complete knowledge of all circuits established in the network but rather only local knowledge of available identifiers at a link. Using local identifiers instead of global identifiers for circuits also enables networks to handle a larger number of circuits.

Traffic engineering (TE) consists in optimizing resource utilization in a network by choosing appropriate paths followed by flows of data, according to static or dynamic constraints [39]. A main goal of traffic engineering is to balance the load in the network, i.e., to avoid congestion on links on a network while other links are under-utilized. To achieve such goals, traffic engineering methods can vary from offline capacity planning algorithms to automatic, dynamic changes. Since circuit switching allocates a fixed path for each flow, circuits can be established according to traffic engineering algorithms.

On the other hand, circuit switching networks are not reactive when a network topology change occurs. For instance, on a link failure, all circuits on a failed link are cut and communication is interrupted. Special mechanisms that handle such topological changes have been be devised. Traffic engineering can alleviate the consequences of a link failure by pre-planning failure recovery. A backup circuit can be established at the same time or after the primary circuit used for a communication is set up, and traffic can be rerouted from the failed circuit to the backup circuit if a link of the primary circuit fails. Circuit switching networks are intrinsically sensitive to link failures and rerouting must be performed by additional traffic engineering mechanisms.


Datagram packet switching

Conceived in the 1960's, packet switching is a more recent technology than circuit switching which addresses a disadvantage of circuit switching: the need to allocate resources for a circuit, thus incurring link capacity wastes when no data flows on a circuit. Packet switching introduces the idea of cutting data on a flow into packets which are transmitted over a network without any resource being allocated. If no data is available at the sender at some point during a communication, then no packet is transmitted over the network and no resources are wasted. Packet switching is the generic name for a set of two different techniques: datagram packet switching and virtual circuit packet switching. Here, we give an overview of datagram packet switching.




Figure 1.2: Datagram Packet Switching.

Packets from a given flow are independent and a router can forward two packets from the same flow on two different links.

Different from circuit switching, datagram packet switching does not require to establish circuits prior to transmission of data and terminate circuits after the transmission of data. The switches, called routers, have to make a lookup in the forwarding table, called routing table, for each incoming packet. A routing table contains a mapping between the possible final destinations of packets and the outgoing link on their path to the destination. Routing tables can be very large because they are indexed by possible destinations, making lookups and routing decisions computationally expensive, and the full forwarding process relatively slow compared to circuit switching. In datagram packet switching networks, each packet must carry the address of the destination host and use the destination address to make a forwarding decision. Consequently, routers do not need to modify the destination addresses of packets when forwarding packets.

Since each packet is processed individually by a router, all packets sent by a host to another host are not guaranteed to use the same physical links. If the routing algorithm decides to change the routing tables of the network between the instants two packets are sent, then these packets will take different paths and can even arrive out of order. In Figure 1.2 for instance, packets use two different paths to go from User 1 to User 5. Second, on a network topology change such as a link failure, the routing protocol will automatically recompute routing tables so as to take the new topology into account and avoid the failed link. As opposed to circuit switching, no additional traffic engineering algorithm is required to reroute traffic.

Since routers make routing decisions locally for each packet, independently of the flow to which a packet belongs. Therefore, traffic engineering techniques, which heavily rely on controlling the route of traffic, are more difficult to implement with datagram packet switching than with circuit switching.


Virtual circuit packet switching



Figure 1.3: Virtual circuit packet switching. All packets from the same flow use the same virtual circuit.

Virtual circuit packet switching (VC-switching) is a packet switching technique which merges datagram packet switching and circuit switching to extract both of their advantages. VC-switching is a variation of datagram packet switching where packets flow on so-called logical circuits for which no physical resources like frequencies or time slots are allocated (see Figure 1.3). Each packet carries a circuit identifier which is local to a link and updated by each switch on the path of the packet from its source to its destination. A virtual circuit is defined by the sequence of the mappings between a link taken by packets and the circuit identifier packets carry on this link. This sequence is set up at connection establishment time and identifiers are reclaimed during the circuit termination.


We have seen the trade-off between connection establishment and forwarding time costs that exists in circuit switching and datagram packet switching. In VC-switching, routing is performed at circuit establishment time to keep packet forwarding fast. Other advantages of VC-switching include the traffic engineering capability of circuit switching, and the resources usage efficiency of datagram packet switching. Nevertheless, a main issue of VC-Switched networks is the behavior on a topology change. As opposed to Datagram Packet Switched networks which automatically recompute routing tables on a topology change like a link failure, in VC-switching all virtual circuits that pass through a failed link are interrupted. Hence, rerouting in VC-switching relies on traffic engineering techniques.

In practice, major implementations of VC-switching are X.25 [70], Asynchronous Transfer Mode (ATM [6]) and Multiprotocol Label Switching (MPLS [50]). The Internet, today's most used computer network, is entirely built around the Internet Protocol (IP), which is responsible for routing packets from one host to another. Because of the central role of IP in the Internet, we now discuss how ATM and MPLS interact with IP.

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The source of entertainment has evolved down the ages. But human beings search for entertainment and things that could amuse him or her has been existing since time immemorial. One of the latest form of entertainment for the present civilization is computers. With inbuilt and loaded computer games, availability of softwares which allow you to paint, listen to music, watch videos, movies and also allow you to create music or videos or movies; computer has really become a major source of entertainment for the people who are computer savvy or at least computer literate. Other than this, the obvious source of entertainment on computers is the internet which not just connects you to the rest of the world but also allows you to find your amusement right at home. Chat rooms allow us to connect with like minded people and discuss with them about our favourite topics. Messengers also allow us to connect to your friends across the world and talk to them. Websites which carry news and other matters related to entertainment become a major source. Online games allow us to play with other people who have access to that game in a virtual world, while we are all seated in our own room in front of our PCs. Innumerable examples of internet as an entertainment source can be quoted. Now with Microsoft and Google promising to built the complete virtual structures of any city in the world on the internet, people would not have to travel to those people on holidays in order to explore and enjoy the city. They just have to log on to the Google World or the Microsoft site and explore the city online where they can walk down the streets enter buildings and even make purchase while they are gossiping about the prices with the other customers in the shops. Now can there be any doubt that computers are a main source of entertainment and amusement in this generation?

The Advantages (Benefits) of Networking

You have undoubtedly heard the “the whole is greater than the sum of its parts”. This phrase describes networking very well, and explains why it has become so popular. A network isn't just a bunch of computers with wires running between them.

Properly implemented, a network is a system that provides its users with unique capabilities, above and beyond what the individual machines and their software applications can provide.

Most of the benefits of networking can be divided into two generic categories: connectivity and sharing. Networks allow computers, and hence their users, to be connected together. They also allow for the easy sharing of information and resources, and cooperation between the devices in other ways. Since modern business depends so much on the intelligent flow and management of information, this tells you a lot about why networking is so valuable.

Here, in no particular order, are some of the specific advantages generally associated with networking:

o Connectivity and Communication: Networks connect computers and the users of those computers. Individuals within a building or work group can be connected into local area networks (LANs); LANs in distant locations can be interconnected into larger wide area networks (WANs). Once connected, it is possible for network users to communicate with each other using technologies such as electronic mail. This makes the transmission of business (or non-business) information easier, more efficient and less expensive than it would be without the network.

o Data Sharing: One of the most important uses of networking is to allow the sharing of data. Before networking was common, an accounting employee who wanted to prepare a report for her manager would have to produce it on his PC, put it on a floppy disk, and then walk it over to the manager, who would transfer the data to her PC's hard disk. (This sort of “shoe-based network” was sometimes sarcastically called a “sneakernet”.)


True networking allows thousands of employees to share data much more easily and quickly than this. More so, it makes possible applications that rely on the ability of many people to access and share the same data, such as databases, group software development, and much more. Intranets and extranets can be used to distribute corporate information between sites and to business partners.

o Hardware Sharing: Networks facilitate the sharing of hardware devices. For example, instead of giving each of 10 employees in a department an expensive color printer (or resorting to the “sneakernet” again), one printer can be placed on the network for everyone to share.

o Internet Access: The Internet is itself an enormous network, so whenever you access the Internet, you are using a network. The significance of the Internet on modern society is hard to exaggerate, especially for those of us in technical fields.

o Internet Access Sharing: Small computer networks allow multiple users to share a single Internet connection. Special hardware devices allow the bandwidth of the connection to be easily allocated to various individuals as they need it, and permit an organization to purchase one high-speed connection instead of many slower ones.

o Data Security and Management: In a business environment, a network allows the administrators to much better manage the company's critical data. Instead of having this data spread over dozens or even hundreds of small computers in a haphazard fashion as their users create it, data can be centralized on shared servers. This makes it easy for everyone to find the data, makes it possible for the administrators to ensure that the data is regularly backed up, and also allows for the implementation of security measures to control who can read or change various pieces of critical information.

o Performance Enhancement and Balancing: Under some circumstances, a network can be used to enhance the overall performance of some applications by distributing the computation tasks to various computers on the network.

o Entertainment: Networks facilitate many types of games and entertainment. The Internet itself offers many sources of entertainment, of course. In addition, many multi-player games exist that operate over a local area network. Many home networks are set up for this reason, and gaming across wide area networks (including the Internet) has also become quite popular. Of course, if you are running a business and have easily-amused employees, you might insist that this is really a disadvantage of networking and not an advantage!

Computer database is a structured[citation needed] collection of records or data that is stored in a computer system so that a computer program or person using a query language can consult it to answer queries. The records retrieved in answer to queries are information that can be used to make decisions. The computer program used to manage and query a database is known as a database management system (DBMS). The properties and design of database systems are included in the study of information science.

A typical query could be to answer questions such as, "How many hamburgers with two or more beef patties were sold in the month of March in New Jersey?". To answer such a question, the database would have to store information about hamburgers sold, including number of patties, sales date, and the region. The term "database" originated within the computing discipline. Although its meaning has been broadened by popular use, even to include non-electronic databases, this article is about computer databases. Database-like collections of information existed well before the Industrial Revolution in the form of ledgers, sales receipts and other business-related collections of data.