Computer Terms Explained

ADSL

(Asymmetric Digital Subscriber Line)
A method for moving data over regular phone lines.
An ADSL circuit is much faster than a regular phone connection,
and the wires coming into the subscriber's premises are the same
(copper) wires used for regular phone service. An ADSL circuit
must be configured to connect two specific locations, similar
to a leased line.

A commonly discussed configuration of ADSL would allow a subscriber
to receive data (download) at speeds of up to 1.544 megabits
(not megabytes) per second, and to send (upload) data at speeds
of 128 kilobits per second. Thus the 'Asymmetric' part of the
acronym.

Another commonly discussed configuration would be symmetrical:
384 kilobits per second in both directions. In theory ADSL allows
download speeds of up to 9 megabits per second and upload speeds
of up to 640 kilobits per second.
ADSL is often discussed as an alternative to ISDN, allowing higher
speeds in cases where the connection is always to the same place.


Applet

A small Java program that can be embedded in an HTML page.
Applets differ from full-fledged Java applications in that they
are not allowed to access certain resources on the local computer,
such as files and serial devices (modems, printers, etc.), and
are prohibited from communicating with most other computers across
a network. The current rule is that an applet can only make an
Internet connection to the computer from which the applet was
sent.
 

ASCII

American Standard Code for Information Interchange) -- This
is the de facto world-wide standard for the code numbers used
by computers to represent all the upper and lower-case Latin
letters, numbers, punctuation, etc. There are 128 standard ASCII
codes each of which can be represented by a 7 digit binary number:
0000000 through 1111111.


Backbone

A high-speed line or series of connections that forms a major
pathway within a network. The term is relative as a backbone
in a small network will likely be much smaller than many non-backbone
lines in a large network.

Bandwidth

How much stuff you can send through a connection. Usually
measured in bits-per-second. A full page of English text is about
16,000 bits. A fast modem can move about 15,000 bits in one second.
Full-motion full-screen video would require roughly 10,000,000
bits-per-second, depending on compression.

Baud

In common usage the baud rate of a modem is how many bits
it can send or receive per second. Technically, baud is the number
of times per second that the carrier signal shifts value - for
example a 1200 bit-per-second modem actually runs at 300 baud,
but it moves 4 bits per baud (4 x 300 = 1200 bits per second).


Bit

A single digit number in base-2, in other
words, either a 1 or a zero. The smallest unit of computerized
data. Bandwidth is usually measured in bits-per-second. See Also:


Bps

(Bits-Per-Second) - A measurement of how fast data is moved
from one place to another. A 28.8 modem can move 28,800 bits
per second. See Also:


Browser

A Client program (software) that is used to look at various
kinds of Internet resources.


Byte

A set of Bits that represent a single character. Usually there
are 8 Bits in a Byte, sometimes more, depending on how the measurement
is being made.


Certificate Authority

An issuer of Security Certificates used in SSL connections.


CGI

(Common Gateway Interface) -- A set of rules that describe
how a Web Server communicates with another piece of software
on the same machine, and how the other piece of software (the
'CGI program') talks to the web server. Any piece of software
can be a CGI program if it handles input and output according
to the CGI standard.

Usually a CGI program is a small program that takes data from
a web server and does something with it, like putting the content
of a form into an e-mail message, or turning the data into a
database query.
You can often see that a CGI program is being used by seeing
'cgi-bin' in a URL, but not always.


cgi-bin

The most common name of a directory on a web server in which
CGI programs are stored. The 'bin' part of 'cgi-bin' is a shorthand
version of 'binary', because once upon a time, most programs
were refered to as 'binaries'. In real life, most programs found
in cgi-bin directories are text files -- scripts that are executed
by binaries located elsewhere on the same machine.


Client

A software program that is used to contact and obtain data
from a Server software program on another computer, often across
a great distance. Each Client program is designed to work with
one or more specific kinds of Server programs, and each Server
requires a specific kind of Client. A Web Browser is a specific
kind of Client.


Contact Record

In the case of many registries, contact information for technical,
billing and administrative purposes are maintained in their database.
It is important to keep your contact records updated to ensure
that billing and renewal can proceed without problems.


Cookie

The most common meaning of 'Cookie' on the Internet refers
to a piece of information sent by a Web Server to a Web Browser
that the Browser software is expected to save and to send back
to the Server whenever the browser makes additional requests
from the Server.

Depending on the type of Cookie used, and the Browser's settings,
the Browser may accept or not accept the Cookie, and may save
the Cookie for either a short time or a long time.

Cookies might contain information such as login or registration
information, online 'shopping cart' information, user preferences,
etc.

When a Server receives a request from a Browser that includes
a Cookie, the Server is able to use the information stored in
the Cookie. For example, the Server might customize what is sent
back to the user, or keep a log of particular user's requests.

Cookies are usually set to expire after a predetermined amount
of time and are usually saved in memory until the Browser software
is closed down, at which time they may be saved to disk if their
'expire time' has not been reached.
Cookies do not read your hard drive and send your life story
to the CIA, but they can be used to gather more information about
a user than would be possible without them.


DNS

(Domain Naming System)
The DNS is a distributed, replicated hierarchy of name servers
that map a domain name (www.metrocomputers.net)
to an IP address.


Dedicated Server

A Net Infrastructure-owned server that is wholly dedicated
to a single customer task, e.g. email or MS SQL Server.


Domain Name

The unique name that identifies an Internet site. Domain Names
always have 2 or more parts, separated by dots. The part on the
left is the most specific, and the part on the right is the most
general. A given machine may have more than one Domain Name but
a given Domain Name points to only one machine. For example,
the domain names: metrocomputers.net,ftp.metrocomputers.net
can all refer to the same machine, but each domain name can refer
to no more than one machine.
Usually, all of the machines on a given Network will have the
same thing as the right-hand portion of their Domain Names
(metrocomputers.net in the examples above). It is also possible for
a Domain Name to exist but not be connected to an actual machine.
This is often done so that a group or business can have an Internet e-mail
address without having to establish a real Internet site. In
these cases, some real Internet machine must handle the mail
on behalf of the listed Domain Name.


E-Commerce

Electronic Commerce. Refers to the general exchange of goods
and services via the Internet.


E-mail

(Electronic Mail) -- Messages, usually text, sent from one
person to another via computer. E-mail can also be sent automatically
to a large number of addresses (Mailing List).


Ethernet

A very common method of networking computers in a LAN. Ethernet
will handle about 10,000,000 bits-per-second and can be used
with almost any kind of computer.


FAQ

(Frequently Asked Questions) -- FAQs are documents that list
and answer the most common questions on a particular subject.
There are hundreds of FAQs on subjects as diverse as Pet Grooming
and Cryptography. FAQs are usually written by people who have
tired of answering the same question over and over.


Firewall

A combination of hardware and software that separates a LAN
into two or more parts for security purposes.
 

FTP

(File Transfer Protocol) -- A very common method of moving
files between two Internet sites. FTP is a special way to login
to another Internet site for the purposes of retrieving and/or
sending files. There are many Internet sites that have established
publicly accessible repositories of material that can be obtained
using FTP, by logging in using the account name anonymous, thus
these sites are called anonymous ftp servers.


Gateway

The technical meaning is a hardware or software set-up that
translates between two dissimilar protocols, for example Prodigy
has a gateway that translates between its internal, proprietary
e-mail format and Internet e-mail format. Another, sloppier meaning
of gateway is to describe any mechanism for providing access
to another system, e.g. AOL might be called a gateway to the
Internet.


Gigabyte

1024 Megabytes


Gopher

A widely successful method of making menus of material available
over the Internet. Gopher is a Client and Server style program,
which requires that the user have a Gopher Client program. Although
Gopher spread rapidly across the globe in only a couple of years,
it has been largely supplanted by Hypertext, also known as WWW
(World Wide Web). There are still thousands of Gopher Servers
on the Internet and we can expect they will remain for a while.


Hit

As used in reference to the World Wide Web, 'hit' means a
single request from a web browser for a single item from a web
server; thus in order for a web browser to display a page that
contains 3 graphics, 4 'hits' would occur at the server: 1 for
the HTML page, and one for each of the 3 graphics.
'Hits' are often used as a very rough measure of load on a server,
e.g. 'Our server has been getting 300,000 hits per month.' Because
each 'hit' can represent anything from a request for a tiny document
(or even a request for a missing document) all the way to a request
that requires some significant extra processing (such as a complex
search request), the actual load on a machine from 1 hit is almost
impossible to define.


Homepage

Several meanings. Originally, the web page that your browser
is set to use when it starts up. The more common meaning refers
to the main web page for a business, organization, person or
simply the main page out of a collection of web pages, e.g. 'Check
out so-and-so's new Home Page.'
Another sloppier use of the term refers to practically any web
page as a 'homepage,' e.g. 'That web site has 65 homepages and
none of them are interesting.'


Host

Any computer on a network that is a repository for services
available to other computers on the network. It is quite common
to have one host machine provide several services, such as WWW
and USENET.


Hosting

This term can be used to refer to the housing of a web site,
email or a domain.


HTML

(HyperText Markup Language) -- The coding language used to
create Hypertext documents for use on the World Wide Web. HTML
looks a lot like old-fashioned typesetting code, where you surround
a block of text with codes that indicate how it should appear,
additionally, in HTML you can specify that a block of text, or
a word, is linked to another file on the Internet. HTML files
are meant to be viewed using a World Wide Web Client Program,
such as Netscape or Mosaic.


HTTP

(HyperText Transport Protocol) -- The protocol for moving
hypertext files across the Internet. Requires a HTTP client program
on one end, and an HTTP server program on the other end. HTTP
is the most important protocol used in the World Wide Web (WWW).


Hypertext

Generally, any text that contains links to other documents,
words or phrases in the document that can be chosen by a reader
and which cause another document to be retrieved and displayed.


InterNIC

InterNIC currently holds an exclusive contract with the U.S.
government to assign domain names for .COM, .NET and .ORG. Network Solutions
is the company that under contract runs the InterNIC registry.


Intranet

A private network inside a company or organization that uses
the same kinds of software that you would find on the public
Internet, but that is only for internal use. >

As the Internet has become more popular many of the tools used
on the Internet are being used in private networks, for example,
many companies have web servers that are available only to employees.


IP Number

(Internet Protocol Number) -- Sometimes called a dotted quad.
A unique number consisting of 4 parts separated by dots, e.g. 208.210.50.33

Every machine that is on the Internet has a unique IP number
If a machine does not have an IP number, it is not really on
the Internet. Most machines also have one or more Domain Names
that are easier for people to remember.


IRC

(Internet Relay Chat) -- Basically a huge multi-user live
chat facility. There are a number of major IRC servers around
the world which are linked to each other. Anyone can create a
channel and anything that anyone types in a given channel is
seen by all others in the channel. Private channels can (and
are) created for multi-person conference calls.


ISDN

(Integrated Services Digital Network) -- Basically a way to
move more data over existing regular phone lines. ISDN is rapidly
becoming available to much of the USA and in most markets it
is priced very comparably to standard analog phone circuits.
It can provide speeds of roughly 128,000 bits-per-second over
regular phone lines. In practice, most people will be limited
to 56,000 or 64,000 bits-per-second.


ISP

(Internet Service Provider) -- An institution that provides
access to the Internet in some form, usually for money.


Java

Java is a network-oriented programming language invented by
Sun Microsystems that is specifically designed for writing programs
that can be safely downloaded to your computer through the Internet
and immediately run without fear of viruses or other harm to
your computer or files. Using small Java programs (called Applets),
Web pages can include functions such as animations, calculators,
and other fancy tricks.
We can expect to see a huge variety of features added to the
Web using Java, since you can write a Java program to do almost
anything a regular computer program can do, and then include
that Java program in a Web page.


Kilobyte

A thousand bytes. Actually, usually 1024 (2^10) bytes.


LAN

(Local Area Network) -- A computer network limited to the
immediate area, usually the same building or floor of a building.


Leased-line

Refers to a phone line that is rented for exclusive 24-hour,
7 -days-a-week use from your location to another location. The
highest speed data connections require a leased line.


Listserv

The most common kind of maillist, Listservs originated on
BITNET but they are now common on the Internet.


Local Registry Fees

Most TLDs require initial registration fees as well as annual
or bi-annual renewal fees. Prices vary from cost-free to thousands
of dollars per domain depending on the TLD chosen. For example,
.COM domains cost $70 which covers the first two years. Renewal
fees for .COM are $35 annually after the first two years expire.


Megabyte

A million bytes. A thousand kilobytes.

MIME

(Multipurpose Internet Mail Extensions) -- The standard for
attaching non-text files to standard Internet mail messages.
Non-text files include graphics, spreadsheets, formatted word-processor
documents, sound files, etc.

An email program is said to be MIME Compliant if it can both
send and receive files using the MIME standard.

When non-text files are sent using the MIME standard they are
converted (encoded) into text - although the resulting text is
not really readable.

Generally speaking the MIME standard is a way of specifying both
the type of file being sent (e.g. a Quicktime video file), and
the method that should be used to turn it back into its original
form.
Besides email software, the MIME standard is also universally
used by Web Servers to identify the files they are sending to
Web Clients, in this way new file formats can be accommodated
simply by updating the Browsers' list of pairs of MIME-Types
and appropriate software for handling each type.


Mirror

Generally speaking, 'to mirror' is to maintain an exact copy
of something. Probably the most common use of the term on the
Internet refers to 'mirror sites' which are web sites, or FTP
sites that maintain exact copies of material originated at another
location, usually in order to provide more widespread access
to the resource.
Another common use of the term 'mirror' refers to an arrangement
where information is written to more than one hard disk simultaneously,
so that if one disk fails, the computer keeps on working without
losing anything.


Name Servers

A computer that performs the mapping of easily remembered
domain names to IP addresses. Sometimes referred to as a host
server or a DNS server.


Network

Any time you connect 2 or more computers together so that
they can share resources, you have a computer network. Connect
2 or more networks together and you have an internet.


Newsgroup

The name for discussion groups on USENET.


NIC

(Network Interface Card) - which plugs into a computer and adapts the network
interface to the appropriate standard. ISA, PCI, and PCMCIA cards
are all examples of NICs.


NNTP

(Network News Transport Protocol) -- The protocol used by
client and server software to carry USENET postings back and
forth over a TCP/IP network. If you are using any of the more
common software such as Netscape, Internet Explorer,
etc. to participate in newsgroups then you are benefiting from
an NNTP connection.


Node

Any single computer connected to a network.


OC-3

Refers to a circuit that transmits 155,000,000 bits per second.
This is the size of the largest Internet backbone providers networks.


Packet Switching

The method used to move data around on the Internet. In packet
switching, all the data coming out of a machine is broken up
into chunks, each chunk has the address of where it came from
and where it is going. This enables chunks of data from many
different sources to co-mingle on the same lines, and be sorted
and directed to different routes by special machines along the
way. This way many people can use the same lines at the same
time.


Parking (Domain Name)

Registering a domain name requires having a location to host
the site. Parked domain names are registered domain names
that have only a simple "this page reserved" web page
at their domain name address. Typically this is very inexpensive
as few hosting resources are used.


Plug-in

A (usually small) piece of software that adds features to
a larger piece of software. Common examples are plug-ins for
the Netscape browser and web server. Adobe Photoshop also uses
plug-ins.

The idea behind plug-in's is that a small piece of software is
loaded into memory by the larger program, adding a new feature,
and that users need only install the few plug-ins that they need,
out of a much larger pool of possibilities. Plug-ins are usually
developed by a third party.


POP

(Point of Presence, also Post Office Protocol) -- Two commonly
used meanings: Point of Presence and Post Office Protocol. A
Point of Presence usually means a city or location where a network
can be connected to, often with dial up phone lines. So if an
Internet company says they will soon have a POP in Belgrade,
it means that they will soon have a local phone number in Belgrade
and/or a place where leased lines can connect to their network.
A second meaning, Post Office Protocol refers to the way e-mail
software such as Eudora gets mail from a mail server. When you
obtain a SLIP, PPP, or shell account you almost always get a
POP account with it, and it is this POP account that you tell
your e-mail software to use to get your mail.


Port

3 meanings. First and most generally, a place where information
goes into or out of a computer, or both. E.g. the serial port
on a personal computer is where a modem would be connected.

On the Internet port often refers to a number that is part of
a URL, appearing after a colon (:) right after the domain name.
Every service on an Internet server listens on a particular port
number on that server. Most services have standard port numbers,
e.g. Web servers normally listen on port 80. Services can also
listen on non-standard ports, in which case the port number must
be specified in a URL when accessing the server, so you might
see a URL of the form:

gopher://peg.cwis.uci.edu:7000/
shows a gopher server running on a non-standard port (the standard
gopher port is 70). Finally, port also refers to translating
a piece of software to bring it from one type of computer system
to another, e.g. to translate a Windows program so that is will
run on a Macintosh.


PPP

(Point to Point Protocol) -- Most well known as a protocol
that allows a computer to use a regular telephone line and a
modem to make TCP/IP connections and thus be really and truly
on the Internet.


Propagation
The process whereby the nameservers throughout the world have
updated their records for a specific domain. For example, if
you move your domain from one host to another, it will take around
24 hours or so for the new address to broadcast everywhere. During
that 24 hour period, the traffic is decreasing at the old location
and increasing at the new location.


Registrar (Domain Name)

Some registries don't provide the ability for end users to
register domains with them directly. They might require end users
to purchase the domain through an internet provider that is acting
as the registrar.


Registry (Domain Name)

An organization responsible for assigning domain names for
the TLD that they manage. Furthermore, it is their responsibility
to update the global DNS tables that all nameservers use to resolve
domain names. For example, InterNIC is the registry for .COM,
.NET and .ORG domain names.


RFC

(Request For Comments) -- The name of the result and the process
for creating a standard on the Internet. New standards are proposed
and published on line, as a Request For Comments. The Internet
Engineering Task Force is a consensus-building body that facilitates
discussion, and eventually a new standard is established, but
the reference number/name for the standard retains the acronym
RFC, e.g. the official standard for e-mail is RFC 822.


Router

A special-purpose computer (or software package) that handles
the connection between 2 or more networks. Routers spend all
their time looking at the destination addresses of the packets
passing through them and deciding which route to send them on.


Security Certificate

A chunk of information (often stored as a text file) that
is used by the SSL protocol to establish a secure connection.

Security Certificates contain information about who it belongs
to, who it was issued by, a unique serial number or other unique
identification, valid dates, and an encrypted 'fingerprint' that
can be used to verify the contents of the certificate. <BR>
In order for an SSL connection to be created both sides must
have a valid Security Certificate.


Server

A computer, or a software package, that provides a specific
kind of service to client software running on other computers.
The term can refer to a particular piece of software, such as
a WWW server, or to the machine on which the software is running,
e.g. Our mail server is down today, that's why e-mail isn't getting
out. A single server machine could have several different server
software packages running on it, thus providing many different
servers to clients on the network.


SLIP

(Serial Line Internet Protocol) -- A standard for using a
regular telephone line (a serial line) and a modem to connect
a computer as a real Internet site. SLIP is gradually being replaced
by PPP.


SMTP

(Simple Mail Transport Protocol) -- The main protocol used
to send electronic mail on the Internet.

SMTP consists of a set of rules for how a program sending mail
and a program receiving mail should interact. <BR>
Almost all Internet email is sent and received by clients and
servers using SMTP, thus if one wanted to set up an email server
on the Internet one would look for email server software that
supports SMTP.


SNMP

(Simple Network Management Protocol) -- A set of standards
for communication with devices connected to a TCP/IP network.
Examples of these devices include routers, hubs, and switches.

A device is said to be 'SNMP compatible' if it can be monitored
and/or controlled using SNMP messages. SNMP messages are known
as 'PDU's' - Protocol Data Units.

Devices that are SNMP compatible contain SNMP 'agent' software
to receive, send, and act upon SNMP messages.
Software for managing devices via SNMP are available for every
kind of commonly used computer and are often bundled along with
the device they are designed to manage. Some SNMP software is
designed to handle a wide variety of devices.


Spam (or Spamming)

An inappropriate attempt to use a mailing list, or USENET
or other networked communications facility as if it was a broadcast
medium (which it is not) by sending the same message to a large
number of people who didn't ask for it.


SQL

(Structured Query Language) -- A specialized programming language
for sending queries to databases. Most industrial-strength and
many smaller database applications can be addressed using SQL.
Each specific application will have its own version of SQL implementing
features unique to that application, but all SQL-capable databases
support a common subset of SQL.


SSL

(Secure Sockets Layer) -- A protocol designed by Netscape
Communications to enable encrypted, authenticated communications
across the Internet.

SSL used mostly (but not exclusively) in communications between
web browsers and web servers. URL's that begin with 'https' indicate
that an SSL connection will be used.

SSL provides 3 important things: Privacy, Authentication, and
Message Integrity.
In an SSL connection each side of the connection must have a
Security Certificate, which each side's software sends to the
other. Each side then encrypts what it sends using information
from both its own and the other side's Certificate, ensuring
that only the intended recipient can de-crypt it, and that the
other side can be sure the data came from the place it claims
to have come from, and that the message has not been tampered
with.


T-1

A leased-line connection capable of carrying data at 1,544,000
bits-per-second. At maximum theoretical capacity, a T-1 line
could move a megabyte in less than 10 seconds. That is still
not fast enough for full-screen, full-motion video, for which
you need at least 10,000,000 bits-per-second. T-1 is the fastest
speed commonly used to connect networks to the Internet.


T-3

A leased-line connection capable of carrying data at 44,736,000
bits-per-second. This is more than enough to do full-screen,
full-motion video.


TCP/IP

(Transmission Control Protocol/Internet Protocol) -- This
is the suite of protocols that defines the Internet. Originally
designed for the UNIX operating system, TCP/IP software is now
available for every major kind of computer operating system.
To be truly on the Internet, your computer must have TCP/IP software.


Telnet

The command and program used to login from one Internet site
to another. The telnet command/program gets you to the login:
prompt of another host.


Terabyte

1024 gigabytes.


Terminal

A device that allows you to send commands to a computer somewhere
else. At a minimum, this usually means a keyboard and a display
screen and some simple circuitry. Usually you will use terminal
software in a personal computer - the software pretends to be
(emulates) a physical terminal and allows you to type commands
to a computer somewhere else.


Terminal Server

A special purpose computer that has places to plug in many
modems on one side, and a connection to a LAN or host machine
on the other side. Thus the terminal server does the work of
answering the calls and passes the connections on to the appropriate
node. Most terminal servers can provide PPP or SLIP services
if connected to the Internet.


Top Level Domain

A Top Level Domain (TLD) is the uppermost in the heirarchy
of domain names. The "net" is considered the TLD and the "metrocomputers.net"
is considered the second level domain. Together they form a domain
name which is unique. There are two types of TLDs. The most common
type is the Generic or Global TLDs which include .COM, .NET,
.ORG, .MIL, .INT and .EDU. There is a possiblity that new gTLDs
will be introduced in the near future. National or ccTLDs are
two letter country code domains that are managed by a registry
designated and controlled by each specific country. Each registry
might have differing prices, residency requirements and structure.



UNIX

A computer operating system (the basic software running on
a computer, underneath things like word processors and spreadsheets).
UNIX is designed to be used by many people at the same time (it
is multi-user) and has TCP/IP built-in. It is the most common
operating system for servers on the Internet.


URL

(Uniform Resource Locator) -- The standard way to give the
address of any resource on the Internet that is part of the World
Wide Web (WWW). A URL looks like this: http://www.metrocomputers.net.

The most common way to use a URL is to enter into a WWW browser
program, such as Netscape, or Internet Explorer.

USENET

A world-wide system of discussion groups, with comments passed
among hundreds of thousands of machines. Not all USENET machines
are on the Internet, maybe half. USENET is completely decentralized,
with over 10,000 discussion areas, called newsgroups.


WAIS

(Wide Area Information Servers) -- A commercial software package
that allows the indexing of huge quantities of information, and
then making those indices searchable across networks such as
the Internet. A prominent feature of WAIS is that the search
results are ranked (scored) according to how relevant the hits
are, and that subsequent searches can find more stuff like that
last batch and thus refine the search process.


WAN

(Wide Area Network) -- Any internet or network that covers
an area larger than a single building or campus.


WHOIS

Most registries maintain a database of domain names and their
associated contact information. Users can query these databases
through a program called Whois.


WWW

(World Wide Web) -- Two meanings - First, loosely used: the
whole constellation of resources that can be accessed using Gopher,
FTP, HTTP, telnet, USENET, WAIS and some other tools. Second,
the universe of hypertext servers (HTTP servers) which are the
servers that allow text, graphics, sound files, etc. to be mixed
together.