The time interval between the instant at which a read/write command is given to a memory and the instant when the next such instruction can be issued to the memory (also known as memory cycle time).
Saturday, October 26, 2013
Cyberspace
A term, popularised by author William Gibson, for the shared imaginary reality of computer networks. Some people use cyberspace as a synonym for the Internet. Other hold out for the more complete physical-seeming con-sensual reality of Gibson's novels.
CTD (Cell Transfer Delay)
Cell Transfer Delay.
In ATM, the elapsed time between a cell-exit event at the source UNI and the corresponding cell-entry event at the destination UNI for a particular connection.
CSU (Channel Service Unit)
Channel Service Unit.
Digital interface device that connects end-user equipment to the local digital telephone loop. Often referred to together with DSU, as CSU/DSU.
Cryptography
A system of secret communications to improve the security of confidential computerized files.
Cryptographic Checksum
A one-way function applied to a file to produce a unique "fingerprint" of the file for later reference. Checksum systems are a primary means of detecting filesystem tampering on Unix.
CDDI
A network technology capable of carrying data at 100 Mbps over unshielded twisted pair (UTP) cable. CDDI is a trade name of Crescendo Communications (acquired by Cisco Systems in 1993) and commonly used insetead of the general term Twisted Pair Physical Layer Medium (TP-PMD). TP-PMD is the general ANSI standard name for this FDDI like service. CDDI cable lengths are limited to 100 meters.
Contention
The method a network uses to determine access to a channel when two or more nodes wish to use it at the same time.
Communications Protocol
A set of rules and procedure established to interconnect different computers and communications between them.
Communications Processor
A processing unit that coordinates networks and data communications. Within a computer network, it ensures that data flows to and from different computer systems correctly and effieciently.
Communications Channel
A medium through which data (in the form of electrical signals) is transferred from one location to another.
Collision Domain
In Ethernet, The network area within which frames that have collied are propagated. Repeaters and hubs propagate collisions; LAN switchs, bridges and routers do not. Also called a bandwidth domain.
Collision
Collisions are an error condition in Ethernet networks. A collision occurs when data packets are transmitted at the same time by two different network nodes. This is very common in large networks. There exist technologies like CSMA/CD which checks for collisions in the network and recover. Also in Ethernet, the result of two nodes transmitting simultaneously.
Client/Server Networking
As opposed to peer-to-peer networking, an arrangement in which central computers called servers supply data and peripherals for use by client computers (workstations). Typically, a server contains a large, hard disk that supplies not only data, but also programs. It even executes programs. A server might also supply printers and modems for clients to use on the network. In other words, client/server refers to an architecture for distribued processing between services, CPUs, or even networked computers for more efficient execution.
Client/Server Architecture
A configuration of computers on a network such that computing tasks are specialized-several computers (clients) interface to users while specialized operations are performed on another (typically smaller) group of one or more computers called servers. Structured Query Language (SQL) is typically used by clients to perform operations on data stored in servers.
Client/Server
Distributed computing network systems in which transaction responsibilities are divided into two parts: client and server.
Clients rely on servers for services such as file storage, printing and processing power. Also a computing model in which the application processing load is distributed between a client and a server computer, which share information over a network. Typically, the client is a PC running front-end software that knows how to communicate with the server (usually database server). The client/server model improves performance, because the client and server share the processing load.
Thursday, October 24, 2013
Circuit Switching
The simplest method of data communication in which a dedicated physical path is established between the sending and the receiving stations through the nodes of a network for the complete duration of information exchange.
CIP (Channel Interface Processor)
Channel Interface Processor. Channel attachment interface for Cisco 7000 series routers. The CIP is used to connect a host Mainframe to a control unit, eliminating the need for an FEP for channel attachment.
CHAP
Challenge Handshake Authentication Protocol.
Security feature supported on links using PPP encapsulation that identifies the remote end of a PPP session using a handshake protocol and a variable challenge value that is unique and unpredictable.
Channel
A path of carrying signals between a source and a destination.
A track on a magnetic tape or band on a magnetic drum.
A pathway through which information can be transmitted.
It refers to the user access channel across which frame relay data travels.
Challenge/Response
An authentication technique whereby a server sends an unpredictable challenge to the user, who computers a response using some form of authentication token.
CESoE
Circuit Emulation Services over Ethernet. It is a method of aggregating and packesting synchronous circuits such as T1/E1 over an asynchronous network such as Ethernet.
CER (Cell Error Ratio)
Cell Error Ratio. In ATM, the ratio of transmitted cells that have errors to the total cells sent in a transmission for a specific period of time.
Wednesday, October 23, 2013
Cell
Basic data unit for ATM switching and multiplexing. Cells contain identifiers that specify the data stream to which they belong. Each cell consists of a 5-bytes header and 48-bytes of payload.
Campus Network
A set of LAN segments and building networks in a geographical area that is a few miles in diameter
BUS
Circuits that provide a communication path between two or more devices of a digital computer system.
Bus Topology
Bus networks (not to be confused with the system bus of a computer) 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.
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 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.
BSC (Base Station Controller)
Base Station Controller is the common name for the radio equipment located at one fixed lovcation, which is used for serving one or several cells.
Broadcast Domain
The set of all devices that receives broadcast frames originating from any device within the set. Broadcast domains are bounded by routers (which do not forward broadcast frames). A switch or hub does not bound a broadcast domain.
Broadcast Address
Special address reserved for sending a message to all nodes. Genarally, a broadcast address is a MAC destination address of all ones (FF:FF:FF:FF:FF:FF: in hexadecimal). Compare with multicast address and unicast address.
Boradband System
A network system in which several analog signals share the same physical network channel.
Broadband Channel
The fastest carriers which have data transfer rates of 1 million boud (bits/second) or more.
BOOTP
Bootstrap Protocol. Protocol used by a network node to determine tha IP address of its interfaces in order to achieve network booting.
Bluetooth
An open specification for short range wireless transmission of voice and data that is currently under developemt. Bluetooth provides a simple, low cost method of linking Personal Digital Assistants (PDAs), cellular phones, laptops and other information appliances.Saturday, October 19, 2013
BLOB (Binary Large Object)
Binary Large Object. Essentially, a long bit string used for complex data.
BISYNC
Abbreviation for binary synchronous. A method of transmitting data- a half-duplex, character-oriented, synchronous data communications transmission method originated by IBM in 1964.
Binary Transfer Protocol
When using a communications program to transmit binary files, it is very important to ensure that errors are not introduced into the data stream. Various binary transfer protocols check for matches between the data transmitted and the data received. The most common protocols are Xmodem, Ymodem, and Zmodem.
Binaries Newsgroup
A Usenet newsgroup dedicated to the posting of uuen-coded binary files, often .gif or .jpg image files. Some sites will not carry binaries newsgroups because their uuen-coded binaries consume so much band width.
BGP (Border Gateway Protocol)
Border Gateway Protocol. Inter-domain routing protocol that exchanges reachability information with other BGP systems. BGP Versions 4 (BGP4) is a predoaminant inter-domain routing protocol used on the Internet.
BER (Bit Error Rate)
Bit Error Rate. It is a ratio of received bits that contain errors to the total number of received bits.
Baseline
Characterization of the normal traffic flow and performance of a network used as input to a new or inhanced design for the network.
Bar Code
A coding structure in which characters are represented by means of a series of parallel bars.
Bandwidth Domain
In a LAN, the set of drvices that share and compete of bandwidth. Bandwidth domains are bounded by switches, bridges, or routers. A hub or repeater does not bound a bandwidth domain. Also called a collision domain on Ethernet networks.
Bandwidth
The range of frequencies available for data transmission. The wider the bandwidth of a communications system, the more data it can transmit in a given period of time. It is expressed in Kilobits persecond's. The bandwidth determines the rate at which information can be sent through a communication channel.
Automatic Teller Machine (ATM)
The ATM is a terminal of the bank's computer network and is operated by a customer himself through a VDU and a keyboard. The customer is given a plastic card at the time of opening his account. The name of the account holder and the account number are magnetically coded on the card. The customer is also given a PIN (Personal Identification Number) which is only known to him. When the customer inserts his card in the ATM, it checks the magnetically coded data and identifies the customer. He then types in his PIN and the amount is withdrawn. The ATM checks the balance and gives out the currency along with a statement of the transaction. The amount gets debited from the account.
Authorization
The process of determining what types of activities are permitted. Usually, authorization is in the context of authentication, once you have authenticated a user, they may be authorized differet types of access or activity.
What is Authentication?
The process of determining the identity of a user who is attempting to access a system. Also in security, the varification of the identity of a person or process.
In a multiuser or network operating system, the process through which the system validates a user's logon information.
In a multiuser or network operating system, the process through which the system validates a user's logon information.
Authentication Token
A portable device used for authenticating a user. Authentication tokens operate by challenge/response, time based code sequences, or other techniques. This may include paper-based lists of one-time passwords.
Audit Trail
A feature of data processing systems that allows for study of data as processed from step to step. In this, an auditor can trace all transactions that affect an account.
ATM Switch
A device that controls information traffic between PCs or workstation using high speed link.
Asynchronous Transfer Mode
ATM is a switching and multiplexing technology that enable voice, data and video to be tansmitted simultaneously over WAN's at high speed regardless of traffic, data is converted into fixed length (53-byte) packet called cells, that are transported at high speeds through the network. These cells are then converted back to their respective traffic types at the destination.
Asynchronous Routing
A function of a remote access server that provides layer-3 routing functionality to connect LAN's via an asynchronous serial WAN link.
What is ASCII?
ASCII stands for American Standard Code for Information Interchange. ASCII is a 7 or 8 bit code used to represent numeric, alphabetic and special printable characters. It also includes codes for control characters, which are not printed or displayed but specify some control functions.
a standard coding system for computers. ASCII-7 is a 7-bit code and its extended version ASCII-8 is an 8-bit code.
a standard coding system for computers. ASCII-7 is a 7-bit code and its extended version ASCII-8 is an 8-bit code.
Friday, October 18, 2013
ASCII File
It is a document file in the universally recognized text format called ASCII (American Standard Code for Information Interchange). An ASCII file contains characters, space, punctuation, carriage return, and sometimes tabs and an end-of-file maker, but it contains no formatting information.
ARCNET
Attached Resource Computer Network 2.5 Mbps token-bus LAN developed in the late 1970's and early 1980s by Datapoint Corporation.
Application Level Firewall
A firewall system in which services is provided by processes that maintain complete TCP connection state and sequencing. Application level firewalls often re-address traffic so that outgoing traffic appears to have originated from the firewall, rather than the internal host.
Application Layer
Layer 7 of the OSI reference model. This layer provides services to application processes (such as electronic mail, file transfer, and terminal emulation) that are outside the OSI model. This application layer identifies and establishes the availability of intended communication partners (and the resources required to connect with them), synchronizes cooperating applications and establishes agreement on procedures for error recovery and control of data integrity.
APPC
Advanced Program-to-Program Communication. IBM SNA system software that allows high speed communication between programs on different computers in a distributed computing environment.
API (Application Program Interface)
An acronym for Application Program Interface. Foxpro's API allows your C and assembly language routines to intract with FoxPro.
Antenna
The part of a transmitting or receiving system that is designed to radiate or to receive electromagnetic waves.
Anonymous FTP
The most common use of FTP, the Internet File Transfer Protocol. FTP sites that allow anonymous FTP do not require a password or access one only has to log in as anonymous and enter one's E-mail address as a password.
Analog Transmission
A continuously varying electromagnetic wave that may be propagate over a variety of media.
Agent
In network management, a process that resides in managed device and reports the values of specified variables to managed stations.
APF (Apple Talk Filing)
Apple Talk Filing Protocol. Application and presentation layer protocol that allows users to share data files and application programs that reside on a file server.
Thursday, October 17, 2013
Network adapter
A network adapter is the hardware installed in computers that enable them to communicate on a network.
Active Monitor
Device responsibel for monitoring a Token Ring. The active monitor ensures that tokens are not lost and that frames do not circulate indefinitely.
Action Entry
The lower right quadrant of a decision table indicating the response to the question entered in the condition entry.
Acoustic coupler
A specific type of modern (communications device) which allows an ordinary telephone to be used with a computer device for data transmission.
ACK (Acknowledgement )
Acknowledgement from a computer that a packet of data has been received and verified.
Account
A form of access to a computer or network for a specific used name and password usually with a home directory, an E-mail in box, and a set of access privileges.
Account
A form of access to a computer or network for a specific used name and password usually with a home directory, an E-mail in box, and a set of access privileges.
Access Router
A router that connects your network to the external Intenet. Typically, this is your first line of defense against attackers from thw outside Internet. By enabling access control lists on this router, you'll be able to provide a level of protection for all of the hots "behind" that router, effectively making that network a DMZ instead of an unprotected external LAN.
Access Method
A standardized procedure for locating desired records within a file. Access methods may be supported by a DATABASE MANAGEMENT SYSTEM or by an OPERATING SYSTEM.
Access Control List (ACL)
Rules for packet filters (typically routers) that defines which packets to pass and which to block.
Abuse of Privilege
When a user performs an action that they should not have, according to organizational policy or law.
Abstract Syntax
A machine independent set of language constructs and rules used to describe objects, protocols and other items.
Abstract Syntax Notation One (ASN.1)
A machine independent, abstarct syntax developed as part of the OSI Reference Model. ASN.1 is used to describe data structure and functions as a common syntax for sending data between two end systems that use different encoding systems.
32-bit
In Windows, refers to the way memory is accessed. 32-bit applications access memory in 32-bit "chunks" (4 bytes). Large portions of Windows 95 and many of its new applications are 32-bit applications, and may run faster because it has become more efficient to access chunks of memory.
Ring Topology
In ring topology, computers are arranged in a circle. Data travels around the ring in one direction, with each device on the ring acting as a repeater. Ring network typically use a token passing protocol.
In ring topology, the nodes are connected in a circle using cable segments. In this layout, each node is physically connected to only two others nodes. Each nodes passes information along to the next, until it arrives at its intended destination. Since each computers re-transmits what it receives, a ring is an active network and is not subject to the single loss problems which a bus topology experiences. There is no termination because there is no end to the ring.Performance on this type of topology is faster because each portion of the cabling system is handling only the data flow between two machines. This type of topology can be found in peer-to-peer networks, in which machine manages both information processing and the distribution of data files.
Advantages of Ring Topology
1. Because every computer is given equal access to the token, no one computer can monopolize the network.
2. The fair sharing of the network allows the network to degrade gracefully. It continuous to function in a slower, manner rather than fail.
Disadvantages of Ring Topology
1. Failure of one computer on the ring affect the whole network.
2. It is difficult to troubleshoot a ring network.
3. Adding or removing computers disrupts the network.
Star Topology
Each computer on a network communicates with a central hub that re-sends the message either to all the computers (in a broadcast star network) or only to the destination computer (in a switched star network). The hub in a broadcast star network can be active or passive.
An active hub regenerate the electrical signal and sends it to all the computers connected to it. This type of hub is often called a multiport repeater. Active hub and switches require electrical power to run. A passive hub merely acts as a connector point and does not amplify or regenerate the signals. Passive hubs do not require electrical power to run.You can use several types of cable to implement a star network. Hybrid hub can accommodate several types of cable in the same star network. You can expand a star network by placing another star hub where a computer might otherwise go, allowing several more computers or hubs to be connected to that hub. This created a hybrid star network.
Advantages of Star Topology
1. It is much easier to modify or add new computers to a star network without disturbing the rest of the network. You simply run a new line from the computer to the central location and plug it into the hub. When the capacity of the central hub is exceeded, you can replace it with one that has a larger number of posts to plug lines into it.
2. The center of a star network is a good place to diagnose network faults. Intelligent hub (hub with microprocessors that implement features in addition to repeating network signals) also provide for centralized monitoring and management of the network.
3. Single computer failures do not necessarily bring down the whole star network. The hub can detect a network fault and isolate the offending computer or network cable and allow the rest of the network to continue its operation.
4. You can use several cable types in the same network with a hub that can accommodate multiple cable types.
Disadvantages of Star Topology
1. If the central hub is fails, the whole network fails to operate.
2. Many star networks require a device at the central point to rebroadcast or switch the network traffic.
3. It costs more to cable a star network because all networks cables must be pulled to one central point, requiring more cable length than other networking topologies.
Accelerator board
A printed circuit board that enhances a computer's performance by substituting a faster microprocessor without replacing the entire motherboard and associated components. Also called accelerator card.
Wednesday, October 16, 2013
Accelerated Hub Architecture (AHA)
Intel Hub Architecture (IHA) is Intel's architecture for the 8xx family of chipsets, starting circa 1999 with the Intel 810. It uses a memory controller hub (MCH) that is connected to an I/O Controller Hub (ICH) via a 266 MB/s bus. The MCH chip supports memory and AGP, while the ICH chip provides connectivity for PCI, USB, sound, IDE hard disks and LAN.
Intel claims that, because of the high-speed channel between the sections, the IHA is much faster than the earlier northbridge/southbridge design, which hooked all low-speed ports to the PCI bus. The IHA also optimizes data transfer based on data type.
AGP (Accelerated Graphics Port)
Short for Accelerated Graphics Port, AGP is an advanced port designed for Video cards and 3D accelerators. Designed by Intel and introduced in August of 1997, AGP introduces a dedicated point-to-point channel that allows the graphics controller direct access the system memory.
AGP is gaming interface, only video card were made for it. AGP is most of the time brown in color and sometimes maroon. AGP more powerfull than PCI, ISA, EISA, Vesta local bus, and MCA when it comes to gaming power. There are many type so know the pinout on the AGP slot on motherboard, the motherboard specs should say something like AGP 4x ect...
The type of AGP:
AGP 1x
AGP 2x
AGP 4x
AGP 8x
AGP Pro
AGP 64 bit
And stuff base off of AGP
AGI
AGX
XGP
You can go to wikipedia.org to find the pinouts.
AGP is being phased out by PCI-Express. AGP video card are still usefull, the newer AGP video cards can handle the new pc games. In a few more years there will be no more company making motherboard with AGP slots on them.
A+ Certification
The CompTIA A+ certification is the starting point for a career in IT. The exams cover maintenance of PCs, mobile devices, laptops, operating systems and printers.
Certification Information
In order to receive the CompTIA A+ certification, you must pass two exams.
CompTIA A+ 220-801 covers the fundamentals of computer technology, installation and configuration of PCs, laptops and related hardware, and basic networking.
CompTIA A+ 220-802 covers the skills required to install and configure PC operating systems, as well as configuring common features (e.g. network connectivity and email) for mobile operating systems Android and Apple iOS.
The previous version of the CompTIA A+ certification, exam codes 220-701 and 220-702, is no longer available in English or academic versions. All other language versions will be available through Dec. 31, 2013. You can take either the two 700 series exams or the two 800 series exams to become CompTIA A+ certified.
CompTIA A+ certifications issued in 2011 or later are valid for three years. You can keep your certification current through the Continuing Education Program.
Test Details
Required exams CompTIA A+ 220-801
CompTIA A+ 220-802
Number of questions Maximum of 90
Type of questions Multiple choice and performance-based
Length of test 90 minutes
Recommended experience Six to 12 months hands-on experience in the lab or field
Passing score CompTIA A+ 220-801: 675 (on a scale of 900)
CompTIA A+ 220-802: 700 (on a scale of 900)
Languages English, German, Japanese, Spanish
Monday, October 14, 2013
What is Repeaters ?
All transmission media attenuate (weaken) the electromagnetic waves that travel through the media. Attenuation therefore limits the distance any medium can carry data. Adding a device that amplifies the signal can allow it to travel farther, increasing the size of the network. For example, if one is connecting computers that are more than 100 meters apart using Ethernet cable, one will need a device that amplifies signals to ensure data transmission. Devices that amplify signals in this way are called repeaters.
Repeaters are fall into the following categories:
Repeaters are fall into the following categories:
a) Amplifiers
b) Signal-regenerating devices (Repeaters)
Amplifiers
Amplifiers simply increase the power of the incoming signal, i.e. both signal and the noise. These are able to improve signal to noise in the analog type systems only.
Signal regenerating repeaters
Signal regenerating repeaters create an exact duplicate of the incoming digital data by identifying it amidst the noise, reconstructing it and passing only the desired information. In this manner, the original signal is duplicated, boosted to its original strength and then sent.
What is the use of repeaters ?
Repeaters extend the distance of a single network. So if you are using an Ethernet LAN but need to go farther than you are usually able to, you can then install a repeater to achieve the added distance. When a repeater is installed, it creates a physical break in the cable. The signal is received on one side of the repeater, regenerated and passed on to the next section of cable.
Subscribe to:
Posts (Atom)