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Apache is a freely available Web server which is distributed under an "open source" license. Apache Version 2.0 runs on most Unix-based operating systems including Linux, Solaris , AIX and other UNIX/POSIX- derived systems. Almost 60% of the web site uses Apache according to a recent survey conducted by

Asynchronous Replication

A technique used for replicating data between databases (or file systems), where the system being replicated does not wait for the data to have been recorded on the duplicate/replicated system before proceeding. Asynchronous Replication has the advantage of speed, but poses risk of data loss during replication due to communication or duplicate/replicate system failure.

See Replication, Synchronous Replication

Application Infrastructure
The infrastructure layer which an application software requires to run the application. This is made of infrastructure components like web servers, application servers commonly termed as a middleware, database servers etc.

Application Architecture

The applications architecture can be defined in simplest terms as a means to manage different or multiple applications and how they work together. Application architecture defines the interaction between the front-end application packages, the middleware and databases. Client/Server, three tier (mostly used in web applications) and Service Oriented Architecture are some of the popular architectures.

Application Clustering

It is also referred to as software clustering. This is done by putting multiple server nodes in to a cluster. These group of servers acts like a single system. Application clustering requires that clustering software is installed in every server node participating in the cluster. The cluster software enables each of the servers maintain the same information. The servers in a cluster collectively performs tasks like load balancing and fail-over.

See also Hardware Clustering ,Clustering, Load Balancing and Fail-Over .



In computer networks, bandwidth is often used as a synonym for data transfer rate i.e., the amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps). Higher the bandwidth, larger the rate of data transfer.


BGP (Border Gateway Protocol) is a protocol for exchanging routing information between gateway hosts (each with its own router) in a network of autonomous systems. BGP is often the protocol used between gateway hosts on the Internet. The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen

See Gateway Nodes, Router

Burstable Bandwidth

A hosting option that allows web sites to use the available network capacity to handle periods of peak usage of bandwidth requirements. Burstable bandwidth is the flexible alternative to dedicated bandwidth. Many infrastructure service providers or hosting providers use this plan as it is cost efficient for both the provider and the tenants of the provider.

See Dedicate Bandwidth

Blade Server

Blade server is a server chassis housing multiple thin, modular electronic circuit boards, known as server blades. Each blade is a server in its own right, often dedicated to a single application. The blades are literally servers on a card, containing processors, memory, integrated network controllers, an optional fiber channel host bus adaptor (HBA) and other input/output (IO) ports.

See Server Blades, HBA, Fiber Channel



Clustering is the technique of using multiple servers, storage devices and interconnecting them to appear like one single system. Typically used for high availability and load balancing.



Direct-attached storage (DAS) is a computer storage that is directly attached to one computer or server. The main alternatives to direct-attached storage are network-attached storage (NAS) and the storage area network (SAN).


DoS Attacks

A denial of service (DoS) attack is an incident in which a user or organization is deprived of the services of a resource they would normally expect to have i.e., website, e-commerce site. In a distributed denial-of-service, large numbers of compromised systems attack a single target

See DDoS Attacks

DDoS Attacks

On the Internet, a distributed denial-of-service (DDoS) attack is one in which a multitude of compromised systems attack a single target, thereby causing denial of service for users of the targeted system. The flood of incoming messages to the target system essentially forces it to shut down, thereby denying service to the system to legitimate users.

See DoS Attacks


The Domain Name System (DNS) is the way the Internet domain names are located and translated into IP (Internet Protocol Addresses) . A domain name is a meaningful and easy-to-remember "handle" for an Internet address. Lists of domain names and IP addresses are distributed throughout the Internet in a hierarchy of authority.



Failover is a backup operational mode in which the functions of a system component (such as a processor, server, network, or database, for example) are assumed by secondary system components when the primary component becomes unavailable through either failure or scheduled down time. To make systems more fault-tolerant, failover is typically an integral part of mission-critical systems that must be constantly available.

See Fault-tolerant


Fault-tolerant can be described as design of computer systems or components so that, in the event that a component or system fails, a backup component or procedure can immediately take its place with no loss of service. Fault tolerance can be provided with software, or embedded in hardware, or provided by some combination.

Fiber Channel

Fibre Channel is a technology for transmitting data between computer devices at data rates of up to 20 Gbps. Fibre Channel is especially suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives. Since Fibre Channel is many times faster, it has begun to replace the Small Computer System Interface (SCSI) as the transmission interface between servers and clustered storage devices



A firewall is a set of related programs, located at a network gateway node, that protects the resources of a private network from users from other networks. The term also implies the security policy that is used within the organization and its applications. Basically, a firewall, working closely with a router program, examines each network packet to determine whether to forward it toward its destination. A firewall can also include working with a proxy server that makes network requests on behalf of workstation users. A firewall is often installed in a specially designated computer separate from the rest of the network so that no incoming request can get directly at private network resources.


Gateway Nodes

A gateway is a point in the network which acts as an entrance to another network. On the Internet, a node can be either a gateway node or a host (end-point) node. The computers that control traffic within a company's network or at local Internet service provider are gateway nodes

Grid Computing

Grid computing (or the use of a computational grid) is applying the resources of many computers in a network to a single problem at the same time - usually to a scientific, complex mathematical or technical problem that requires a great number of computer processing cycles or access to large amounts of data. A well-known example of grid computing in the public domain is the ongoing SETI (Search for Extraterrestrial Intelligence).


HBA- Host Bus Adapter

A Host Bus Adapter (HBA) is a circuit board and/or integrated circuit adapter that provides input/output (I/O) processing and physical connectivity between a server and a storage device. Because HBA relieves the host microprocessor of both data storage and retrieval tasks, it can improve the server's performance time. HBA and its associated disk subsystems are sometimes referred to as a disk channel.

Hardware Clustering

Hardware clustering (sometimes called operating system clustering) is a hardware-based method of turning multiple servers into a cluster (a group of servers that acts like a single system). Each of the participating servers functions independently of the others, although they all respond to the same requests. The operating system of the controlling server is responsible for monitoring the cluster and performing administrative tasks, such as deciding when failover is necessary and assigning the load of a failed node to a functioning server.

See Failover

HTML or Hyper-Text Markup Language

HTML (Hypertext Markup Language) is the set of markup symbols or codes inserted in a text or file which is to be displayed on browser page. The markup tells the browser how to display a Web page's words and images. Markup code is referred to as a tag as well. HTML is the formal recommendation by the World Wide Web Consortium (W3C) and is generally adhered to by the major browsers.



Intrusion detection (ID) is a type of security management system for computers and networks. An ID system gathers and analyzes information from various areas within a computer or a network to identify possible security breaches, which include both intrusions (attacks from outside the organization) and misuse (attacks from within the organization). ID uses vulnerability assessment technology to assess the security of a computer system or network.

See IPS, DoS, DDoS


Intrusion Prevention System is a preemptive approach to network security used to identify potential threats and respond to them swiftly. Like an Intrusion Detection System (IDS), an Intrusion Prevention System (IPS) monitors network traffic. However, because an exploit may be carried out very quickly after the attacker gains access, IPS also have the ability to take immediate action, based on a set of rules established by the network administrator. For example, an IPS might drop a packet that it determines to be malicious and block all further traffic from that IP address. Legitimate traffic, meanwhile, is forwarded to the recipient with no apparent disruption or delay of service.

See IDS, DoS, DDoS

IP Storage

Internet Protocol Storage uses the IP protocol to connect storage area networks (SANs) or NAS (Network Attached Storage) in remote locations.

IP or Internet Protocol

IP, short for Internet Protocol is a connectionless protocol or method by which data is sent from one computer to another on the Internet. Each computer (known as a host) on the Internet has at least one IP address that uniquely identifies it from all other computers on the Internet. The messages sent or received on the internet are divided in to chunks called packets. Another protocol called Transmission Control Protocol (TCP) puts these chunks or packets in to the right order.

See IP address, TCP, Packets

IP Address

An IP address is a unique 32 bit number address used to locate and identify a device over a network. The device can be an electronic device, a computer, a server, a router or an IP phone. It is the addressing used for transmission of data packets over a network working with IP protocol

ISP or Internet Service Provider

ISP (Internet service provider) is a company that provides individuals and other companies access to Internet and other related services such as web site hosting and virtual hosting. An ISP needs to have the telecommunication infrastructure to have a point-of-presence on the Internet for the geographic area served.

See Virtual Hosting, Point-of-Presence ( POP)


Internet SCSI is a protocol that serializes SCSI commands and converts them to TCP/IP. ISCI protocol is used for connecting SAN and NAS devices to servers as a cost-effective alternative to Fiber channel connectivity.

See IP Storage, SCSI, SAN, NAS


Load Balancing

Load balancing can be termed as distributing the work load that a computer has to do among two or more computers. This facilitates more workload to be processed in the same amount of time and user’s requests get served faster. Load balancing widely is used in web applications. Load balancing can be implemented through application and hardware clustering or a combination of both.

See Hardware Clustering, Software Clustering



Network-attached storage (NAS) is hard disk storage that is set up with its own network address rather than being attached to the servers that is serving applications to workstation users. By removing storage access and its management from servers, application programming and files can be served faster. The network-attached storage devices are attached to a local area network (an ethernet network) and assigned an IP address. File requests are mapped by the main server to the NAS file server. NAS device runs a small slimmed-down operating system and a file system and processes only I/O requests. NAS devices support file sharing protocols like CIFS for Windows and NFS for Unix

Network Virtualization

Network virtualization is a method of combining the available resources in a network by splitting up the available bandwidth into channels, each of which is independent from the others, and each of which can be assigned (or reassigned) to a particular server or device in real time. Each channel is independently secured. Every subscriber has shared access to all the resources on the network from a single computer.


On-Demand Computing

On-Demand (OD) computing is an increasingly popular enterprise model in which computing resources are made available to the user as needed. The resources may be maintained within the user's enterprise, or made available by a service provider. On-Demand model was developed to overcome the common challenge to an enterprise of being able to meet fluctuating demands efficiently. Because an enterprise's demand on computing resources can vary drastically from time to time, maintaining sufficient resources to meet peak requirements can be costly. Conversely, if the enterprise cuts costs by only maintaining minimal computing resources, there will not be sufficient resources to meet peak requirements


POP – Point of Presence

On the Internet, a point-of-presence (POP) is an access point from one place to rest of the Internet. (POP also stands for the e-mail Post Office Protocol; POP3.)

See POP3 ( Post Office Protocol 3)


POP3 (Post Office Protocol 3) is the version of a standard protocol for receiving e-mail. E-mail is received and held by internet mail server. Periodically, mail client like Outlook, checks respective mail-box on the mail server and download any mail, using POP3.



RAID - Redundant Array of Independent Disks is a disk subsystem which increases performance or provides fault tolerance or both. RAID uses two or more hard drives and a RAID controller. In the late 1980s, the "I" in RAID stood for "inexpensive," but was later changed to "independent.”. Raid is a way of storing the same data in different places (thus achieving redundancy) on multiple hard disks. By placing data on multiple disks, I/O (input/output) operations can overlap in a balanced way, improving performance.


In packet networks such as the Internet, a router is a device which determines the next network point to which a packet should be forwarded toward its destination. The router is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to. A router is located at any gateway, including each point-of-presence on the Internet. A router is often included as part of a network switch.

See Gateway Nodes, POP



SAN - Storage Area Network is a network of storage devices. A SAN can connect multiple servers to a centralized pool of disk storage. Compared to managing hundreds of servers, each with their own disks, SANs improve system administration tasks. By treating all the company's storage as a single resource, disk maintenance and routine backups are easier to schedule and control.

Server Blades

A server blade is a thin, modular electronic circuit board containing one, two, or more microprocessors and memory, that is intended for a single, dedicated application (such as serving Web pages) and that can be easily inserted into a blade server, which is a space-saving rack with many similar servers. One product offering, for example, makes it possible to install up to 280 blade server modules vertically in multiple racks or rows of a single floor-standing cabinet. Blade servers, which share a common high-speed bus, are designed to create less heat and thus save energy costs as well as space.

Server Virtualization

Server virtualization is the masking of server resources, including the number and identity of individual physical servers, processors, and operating systems, from server users. The server administrator uses a software application to divide one physical server into multiple isolated virtual environments. The virtual environments are sometimes called virtual private servers, but they are also known as partitions, guests, instances, containers or emulations.

There are three popular approaches to server virtualization: the virtual machine model, the para - virtual machine model, and virtualization at the operating system layer.

Storage Virtualization

Virtualization is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Storage virtualization is commonly used in a storage area network (SAN). Management of storage devices can be tedious and time-consuming. Storage virtualization helps the storage administrator perform the tasks of backup, archiving, and recovery more easily, and in less time, by disguising the actual complexity of the SAN. Users can implement virtualization with software applications or by using hardware and software hybrid appliances. The technology can be placed on different levels of a storage area network.


In a telecommunications network, a switch is a device that channels incoming data from any of multiple input ports to the specific output port that will take the data toward its intended destination.

Synchronous Replication

Synchronous Replication is technique for replicating data between databases (or file systems) where the system being replicated does wait for the data to have been recorded on the duplicate system before proceeding. Synchronous Replication has the advantage that it is guaranteed that the duplicate system has a copy of the data, but the disadvantage that the primary system must wait for the secondary system before proceeding, leading to an increased response time. Because of the increased response time and communication delays, synchronous replication is often impractical.

See Asynchronous Replication


TCP or Transmission Control Protocol

TCP is a connection-oriented protocol and manages division of IP messages into packets from senders end and also reassembling packets in order at the receiving end. Unlike Internet Protocol, a connection is established and maintained until such time as the message or messages to be exchanged by the application programs at each end (origin and destination) have been exchanged.


Utility Computing

Utility computing is a service provisioning model in which a service provider makes computing resources and infrastructure management available to the customer as needed, and charges them for specific usage rather than a flat rate. Like other types of on-demand computing (such as grid computing), the utility model seeks to maximize the efficient use of resources and/or minimize associated costs

See On-demand computing, grid computing


Virtual Hosting

On the Internet, virtual hosting is the provision of Web Server hosting services so that a company (or individual) doesn't have to purchase and maintain its own Web Server and connections to the Internet


Virtualization is the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources.

See Server virtualization, storage virtualization and Network virtualization