Access Controls An access control system

Semantic mapping

Computer multiprogramming is the allocation of a computer system and its resources to more than one concurrent application, job or user ("program" in this nomenclature).

Initially, this technology was sought in order to optimize use of a computer system, since time and processing resources were often wasted when a single job waited for human interaction or other data input/output operations.

Multiprogramming capability was developed as a feature of operating systems in the late 1950s and came into common use in mainframe computing in the mid- to late 1960s. This followed the development of hardware systems that possessed the requisite circuit logic and instruction sets to facilitate the transfer of control between the operating system and one or more independent applications, users or job streams.

The use of multiprogramming was enhanced by the arrival of virtual memory and virtual machine technology, which enabled individual programs to make use of memory and operating system resources as if other concurrently running programs were, for all practical purposes, non-existent and invisible to them.

Multiprogramming should be differentiated from multi-tasking since not all multiprogramming entails—or has the capability for-- "true" multi-tasking. This is the case even though the use of multi-tasking generally implies the use of some multiprogramming methods.

In this context, the root word "program" does not necessarily refer to a compiled application, rather, any set of commands submitted for execution by a user or operator. Such could include a script or job control stream and any included calls to macro-instructions, system utilities or application program modules. An entire, interactive, logged-in user session can be thought of as a "program" in this sense.

A program generally comprises numerous tasks, a task being a relatively small group of processor instructions which together achieve a definable logical step in the completion of a job or the execution of a continuous-running application program. A task frequently ends with some request requiring the moving of data, a convenient opportunity to allow another program to have system resources, particularly CPU time.

In multiprogramming, concurrent running (sharing of the processor) is achieved when the operating system identifies opportunities to interrupt the handling of one program between tasks (e.g., when it is waiting for input/output) and to transfer process control to another program (application, job or user). To a great extent, the ability of a system to share its resources equitably—or according to certain priorities—is dependent upon the design of the programs being handled and how frequently they may be interrupted.

Multi-tasking eliminates that dependency and expands upon multiprogramming by enabling the operating system supervisor to interrupt programs in the middle of tasks and to transfer processor control so rapidly that each program is now assured a portion of each processing second, making the interruptions imperceptible to most human-interactive applications.

A computer network allows computers to communicate with many other and to share resources and information. The Advanced Research Projects Agency (ARPA) funded the design of the "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense. It was the first operational computer network in the world.^[1] Development of the network began in 1969, based on designs begun in the 1960s.

[edit] Network classification

The following list presents categories used for classifying networks.

[edit] Connection method

Computer networks can also be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as Optical fiber, Ethernet, Wireless LAN, HomePNA, Power line communication or G.hn. Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.

ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.

Wired Technologies

Twisted-Pair Wire - This is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed range from 2 million bits per second to 100 million bits per second.

Coaxial Cable – These cables are widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.

Fiber Optics – These cables consist of one or more thin filaments of glass fiber wrapped in a protective layer. It transmits light which can travel over long distance and higher bandwidths. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed could go up to as high as trillions of bits per second. The speed of fiber optics is hundreds of times faster than coaxial cables and thousands of times faster than twisted-pair wire.

Wireless Technologies

Terrestrial Microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx. 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.

Communications Satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.

Cellular and PCS Systems – Use several radio communications technologies. The systems are divided to different geographic area. Each area has low-power transmitter or radio relay antenna device to relay calls from one area to the next area.

Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANS use spread spectrum technology to enable communication between multiple devices in a limited area. Example of open-standard wireless radio-wave technology is IEEE 802.11b.

Bluetooth – A short range wireless technology. Operate at approx. 1Mbps with range from 10 to 100 meters. Bluetooth is an open wireless protocol for data exchange over short distances.

The Wireless Web – The wireless web refers to the use of the World Wide Web through equipments like cellular phones, pagers,PDAs, and other portable communications devices. The wireless web service offers anytime/anywhere connection.

[edit] Scale

Networks are often classified as Local Area Network (LAN), Wide Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network (PAN), Virtual Private Network (VPN), Campus Area Network (CAN), Storage Area Network (SAN), etc. depending on their scale, scope and purpose. Usage, trust levels and access rights often differ between these types of network - for example, LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations (such as a building), while WANs may connect physically separate parts of an organization to each other and may include connections to third parties.

Network Administrator

Network administrator is a modern profession responsible for the maintenance of computer hardware and software that comprises a computer network. This normally includes the deployment, configuration, maintenance and monitoring of active network equipment. A related role is that of the network specialist, or network analyst, who concentrates on network design and security.

The Network Administrator is usually the highest level of technical/network staff in an organization and will rarely be involved with direct user support. The Network Administrator will concentrate on the overall health of the network, server deployment, security, and ensuring that the network connectivity throughout a company's LAN/WAN infrastructure is on par with technical considerations at the network level of an organization's hierarchy. Network Administrators are considered Tier 3 support personnel that only work on break/fix issues that could not be resolved at the Tier1 (helpdesk) or Tier 2 (desktop/network technician) levels.

Depending on the company, the Network Administrator may also design and deploy networks. However, these tasks may be assigned to a Network Engineer should one be available to the company.

The actual role of the Network Administrator will vary from company to company, but will commonly include activities and tasks such as network address assignment, assignment of routing protocols and routing table configuration as well as configuration of authentication and authorization – directory services. It often includes maintenance of network facilities in individual machines, such as drivers and settings of personal computers as well as printers and such. It sometimes also includes maintenance of certain network servers: file servers, VPN gateways, intrusion detection systems, etc.

Network specialists and analysts concentrate on the network design and security, particularly troubleshooting and/or debugging network-related problems. Their work can also include the maintenance of the network's authorization infrastructure, as well as network backup systems.

The administrator is responsible for the security of the network and for assigning IP addresses to the devices connected to the networks. Assigning IP addresses gives the subnet administrator some control over the professional who connects to the subnet. It also helps to ensure that the administrator knows each system that is connected and who personally is responsible for the system.

Network Operating System

A networking operating system is an operating system that contains components and programs that allow a computer on a network to serve requests from other computer for data and provide access to other resources such as printer and file systems.

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