|
Jump to: A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
Analog: Almost everything in the world can be described or represented in one of two forms: analog or digital. The principal feature of analog
representations is that they are continuous. In contrast digital representations consist of values measured at discrete intervals.
Digital watches are called digital because they go from one value to the next without displaying all intermediate values. Consequently they can
display only a finite number of times of the day. In contrast watches with hands are analog because the hands move continuously around the
clock face. As the minute hand goes around it not only touches the numbers 1 through 12 but also the infinite number of points in between.
Early attempts at building computers used analog techniques but accuracy and reliability were not good enough. Today almost all computers are digital.
ADSL: Short for asymmetric digital subscriber line, a new technology that allows more data to be sent over existing copper telephone
lines (POTS). ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps
when sending data (known as the upstream rate). ADSL requires a special ADSL modem. ADSL is growing in popularity as more
areas around the world gain access.
ASP: Abbreviated as ASP, a specification for a dynamically created Web page with a .ASP extension that utilizes ActiveX scripting -- usually
VB Script or Jscript code. When a browser requests an ASP, the Web server generates a page with HTML code and sends it back to the
browser. So ASPs are similar to CGI scripts, but they enable Visual Basic programmers to work with familiar tools.
Asymmetric: Providing differing bandwidth in different directions. 56k modems are asymmetrical: 56k for downloading but only 28.8k or 33.6k for uploading.
Authentication: The process of identifying an individual usually based on a username and password.
Database: A collection of information organized in such a way that a computer program can quickly select desired pieces of data. You can think of a
database as an electronic filing system.
Traditional databases are organized by fields, records and files. A field is a single piece of information a record is one complete set of
fields and a file is a collection of records. For example a telephone book is analogous to a file. It contains a list of records each of which
consists of three fields: name address and telephone number.
DHCP: Short for Dynamic Host Configuration Protocol a protocol for assigning dynamic IP addresses to devices on a network. With dynamic
addressing a device can have a different IP address every time it connects to the network. In some systems the IP address of the device can
even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.
Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator
to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique
IP address. Many ISPs use dynamic IP addressing for dial-up users.
Digital: Describes any system based on discontinuous data or events. Computers are digital machines because at their most basic level they
can distinguish between just two values 0 and 1 or off and on. There is no simple way to represent all the values in between such as 0.25. All
data that a computer processes must be encoded digitally as a series of zeroes and ones.
The opposite of digital is analog. A typical analog device is a clock in which the hands move continuously around the face. Such a clock is
capable of indicating every possible time of day. In contrast a digital clock is capable of representing only a finite number of
times (every tenth of a second for example).
In general humans experience the world analogically. Vision for example is an analog experience because we perceive infinitely smooth gradations
of shapes and colors. Most analog events however can be simulated digitally. Photographs in newspapers for instance consist of an array of
dots that are either black or white. From afar the viewer does not see the dots (the digital form) but only lines and shading which appear to be
continuous. Although digital representations are approximations of analog events they are useful because they are relatively easy to store and
manipulate electronically. The trick is in converting from analog to digital and back again.
This is the principle behind compact discs (CDs). The music itself exists in an analog form as waves in the air but these sounds are then
translated into a digital form that is encoded onto the disk. When you play a compact disc the CD player reads the digital data translates it back
into its original analog form and sends it to the amplifier and eventually the speakers.
Internally computers are digital because they consist of discrete units called bits that are either on or off. But by combining many bits in
complex ways computers simulate analog events. In one sense this is what computer science is all about.
Domain Name: A name that identifies one or more IP addresses. For example the domain name microsoft.com represents about a dozen IP
addresses. Domain names are used in URLs to identify particular Web pages. For example in the URL http://www.pcwebopedia.com/index.html the
domain name is pcwebopedia.com.
Because the Internet is based on IP addresses not domain names every Web server requires a Domain Name System (DNS) server to translate
domain names into IP addresses.
Driver: A program that controls a device. Every device whether it be a printer disk drive or keyboard must have a driver program. Many drivers
such as the keyboard driver come with the operating system. For other devices you may need to load a new driver when you connect the device to your computer.
A driver acts like a translator between the device and programs that use the device. Each device has its own set of specialized commands that
only its driver knows. In contrast most programs access devices by using generic commands. The driver therefore accepts generic commands from a
program and then translates them into specialized commands for the device.
E-Commerce: Short for Electronic Commerce, means simply, conducting business on-line.
FCC: Abbreviation of Federal Communications Commission. Among other duties the FCC is responsible for rating personal computers and other equipment as either
Class A or Class B. The ratings indicate how much radiation a personal computer emits. Almost all personal computers satisfy Class A requirements which means
they are suitable for office use. Class B machines which are suitable for use anywhere (including the home) must pass more stringent tests. Class B indicates
that the machines radio frequency (RF) emissions are so low that they do not interfere with other devices such as radios and TVs.
Firmware: Built-in software that controls the operation of a dedicated microprocessor-based device.
FTP: Short for File Transfer Protocol. A protocol used to upload files from a workstation to an FTP server or download files from an FTP server to a workstation. It is the way that files get transferred from one device to another in order for the files to be available on the Internet.
Gateway: A node on a network that serves as an entrance to another network. In enterprises the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes the gateway is the ISP that connects the user to the internet.
HTML: Short for HyperText Markup Language, the authoring language used to create documents on the World Wide Web. HTML defines the structure and layout of a Web document by using a variety of tags and attributes. There are hundreds of other tags used to format and layout the information in a Web page. Tags are also used to specify hypertext links. These allow Web developers to direct users to other Web pages with only a click of the mouse on either an image or words.
HTTP: Short for HyperText Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.
ICANN: Short for Internet Corporation for Assigned Names and Numbers a nonprofit organization that has assumed the responsibility for IP address space allocation protocol parameter assignment domain name system management and root server system management functions previously performed under U.S. Government contract.
ICANN was created by the late Jon Postel in the fall of 1998 in response to a policy statement issued by the US Department of Commerce. This statement called for the formation of a private sector not-for-profit Internet stakeholder to administer policy for the Internet name and address system.
Thus far ICANN has taken various measures to oversee the domain-name registration systems transition from government hands to private hands and to coordinate its decentralization and the integration into a global community.
ICANNs diverse board consists of nineteen Directors nine At-Large Directors who serve one-year terms and will be succeeded by At-Large Directors electedby an at-large membership organization. None of the present interim directors may sit on the board once the permanent members are selected.
ICMP: Short for Internet Control Message Protocol an extension to the Internet Protocol (IP). ICMP supports packets containing error control and informational messages.
InterNIC: Short for Internet Network Information Center a registered service mark of the U.S. Department of Commerce and now a defunct entity. InterNIC began as a collaborative project between AT&T and Network Solutions Inc. (NSI) supported by the National Science Foundation. When active the project offered four services:
- InterNIC Directory and Database Services -- online white pages directory and directory of publicly accessible databases managed by AT&T.
- Registration Services -- domain name and IP address assignment managed by NSI.
- Support Services -- outreach education and information services for the Internet community managed by NSI.
- Net Scout Services -- online publications that summarize recent happenings of interest to Internet users (managed by NSI).
- The InterNIC is currently an informational Web site established to provide the public with information about domain name registration. ICANN now oversees the domain name registration industry.
IP Address: An identifier for a computer or device on a TCP/IP network. Networks using the TCP/IP protocol route messages based on the IP address of the destination. The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example 1.160.10.240 could be an IP address.
Within an isolated network you can assign IP addresses at random as long as each one is unique. However connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.
ISDN: Abbreviation of integrated services digital network an international communications standard for sending voice video and data over digital telephone lines or normal telephone wires. ISDN supports data transfer rates of 64 Kbps (64000 bits per second).
There are two types of ISDN:
Basic Rate (BRI) ISDN -- consists of two 64-Kbps B-channels and one D-channel for transmitting control information.
Primary Rate ISDN -- consists of 23 B-channels and one D-channel (U.S.) or 30 B-channels and one D-channel (Europe).
The original version of ISDN employs baseband transmission. Another version called B-ISDN uses broadband transmission and is able to support transmission rates of 1.5 Mbps. B-ISDN requires fiber optic cables and is not widely available.
ISP: Short for Internet Service Provider a company that provides access to the Internet. For a monthly fee the service provider gives you a software package username password and access phone number. Equipped with a modem you can then log on to the Internet and browse the World Wide Web and USENET and send and receive e-mail.
In addition to serving individuals ISPs also serve large companies providing a direct connection from the companys networks to the Internet. ISPs themselves are connected to one another through Network Access Points (NAPs).
ISPs are also called IAPs (Internet Access Providers).
Java: Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser.
LAN: A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network (WAN).
Most LANs connect workstations and personal computers. Each node (individual computer) in a LAN has its own CPU with which it executes programs but it also is able to access data and devices anywhere on the LAN. This means that many users can share expensive devices such as laser printers as well as data. Users can also use the LAN to communicate with each other by sending e-mail or engaging in chat sessions.
Modem: Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over for example telephone or cable lines. Computer information is stored digitally whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.
MX: Short for Mail eXchange record an entry in a domain name database that identifies the mail server that is responsible for handling e-mails for that domain name.
NAT: Short for Network Address Translation an Internet standard that enables a local-area network (LAN) to use one set of IP addresses for internal traffic and a second set of addresses for external traffic. A NAT box located where the LAN meets the Internet makes all necessary IP address translations.
NAT serves these main purposes:
- Provides a type of firewall by hiding internal IP addresses.
- Enables a company to use more internal IP addresses. Since they are used internally only there is no possibility of conflict with IP addresses used by other companies and organizations.
NNTP: Short for Network News Transfer Protocol the protocol used to post distribute and retrieve USENET messages.
ODBC: Short for Open DataBase Connectivity, a standard database access method developed by Microsoft Corporation. The goal of ODBC is to make it possible to access any data from any application, regardless of which database management system (DBMS) is handling the data.
OLE: Short for Object Linking and Embedding, pronounced as separate letters or as oh-leh. OLE is a compound document standard developed by Microsoft Corporation. It enables you to create objects with one application and then link or embed them in a second application. Embedded objects retain their original format and links to the application that created them.
OSI: Short for Open System Interconnection an ISO standard for worldwide communications that defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next starting at the application layer in one station proceeding to the bottom layer over the channel to the next station and back up the hierarchy.
Packet: A piece of a message transmitted over a network.
One of the key features of a packet is that it contains the destination address in addition to the data.
Perl: Short for Practical Extraction and Report Language, Perl is a programming language developed by Larry Wall, especially designed for processing text. Because of its strong text processing abilities, Perl has become one of the most popular languages for writing CGI scripts. Perl is an interpretive language, which makes it easy to build and test simple programs.
POP3: Short for Post Office Protocol a protocol used to retrieve e-mail from a mail server. Most e-mail applications use the POP protocol although some can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first called POP2 became a standard in the mid-80s and requires SMTP to send messages. The newer version POP3 can be used with or without SMTP.
POTS: Short for plain old telephone service, which refers to the standard telephone service that most homes use. In contrast, telephone services based on high-speed, digital communications lines, such as ISDN and FDDI, are not POTS. The main distinctions between POTS and non-POTS services are speed and bandwidth. POTS is generally restricted to about 52 Kbps (52,000 bits per second). The POTS network is also called the public switched telephone network (PSTN). POTS should not be confused with pot, an abbreviation of potentiometer.
Router: A device that forwards data packets along networks. A router is connected to at least two networks commonly two LANs or WANs or a LAN and its ISPs network. Routers are located at gateways the places where two or more networks connect.
Routers use headers and forwarding tables to determine the best path for forwarding the packets and they use protocols such as ICMP to communicate with each other and configure the best route between any two hosts.
Server: A computer or device on a network that manages network resources. For example a file server is a computer and storage device dedicated to storing files. Any user on the network can store files on the server. A print server is a computer that manages one or more printers and a network server is a computer that manages network traffic. A database server is a computer system that processes database queries.
Servers are often dedicated meaning that they perform no other tasks besides their server tasks. On multiprocessing operating systems however a single computer can execute several programs at once. A server in this case could refer to the program that is managing resources rather than the entire computer.
SMTP: Short for Simple Mail Transfer Protocol a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
Spam: Electronic junk mail or junk newsgroup postings. Some people define spam even more generally as any unsolicited e-mail. However if a long-lost brother finds your e-mail address and sends you a message this could hardly be called spam even though it is unsolicited. Real spam is generally e-mail advertising for some product sent to a mailing list or newsgroup.
SQL: Short for Structured Query Language, and pronounced either see-kwell or as separate letters. SQL is a standardized query language for requesting information from a database.
Subnet: A portion of a network that shares a common address component. On TCP/IP networks subnets are defined as all devices whose IP addresses have the same prefix. For example all devices with IP addresses that start with 100.100.100. would be part of the same subnet. Dividing a network into subnets is useful for both security and performance reasons. IP networks are divided using a subnet mask.
A mask used to determine what subnet an IP address belongs to. An IP address has two components the network address and the host address. For example consider the IP address 150.215.017.009. Assuming this is part of a Class B network the first two numbers (150.215) represent the Class B network address and the second two numbers (017.009) identify a particular host on this network.
Switch: In networks a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs or in the case of Ethernet networks switched Ethernet LANs.
TLD: Short for top-level domain and refers to the suffix attached to Internet domain names. There are a limited number of predefined suffixes and each one represent a top-level domain. Current top-level domains include:
- com - commercial businesses (this is the most common TLD)
- gov - U.S. government agencies
- edu - Educational institutions such as universities
- org - Organizations (mostly nonprofit)
- mil - Military
- net - Network organizations
- ca - Canada
- th - Thailand
Usenet: A worldwide bulletin board system that can be accessed through the Internet or through many online services. The USENET contains more than 14000 forums called newsgroups that cover every imaginable interest group. It is used daily by millions of people around the world.
v.34: The standard for full-duplex modems sending and receiving data across phone lines at up to 28800 bps. V.34 modems automatically adjust their transmission speeds based on the quality of the lines.
WAN: A computer network that spans a relatively large geographical area. Typically a WAN consists of two or more local-area networks (LANs).
Computers connected to a wide-area network are often connected through public networks such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.
Whois: An Internet utility that returns information about a domain name or IP address. For example if you enter a domain name such as microsoft.com whois will return the name and address of the domains owner (in this case Microsoft Corporation).
|
