Network Chico Computer
Some definitions from the Sharpened Glossary
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Daemon: A UNIX term for
a component of any server program that "listens" to
incoming requests for a specific service across the network;
for example, a Telnet server might include a Telnet daemon, a
program that always runs, ready to server Telnet requests; the
same component of an FTP server is called an FTP daemon, and
Daily backup: Copies all
files modified on the day of the backup.
DAS: "Dual Attachment
Stations" Computers or concentrators connected to both rings
in an FDDI network.
Database: This is a data
structure used to store organized information. A database is
typically made up of many linked tables of rows and columns.
For example, a company might use a database to store information
about their products, their employees, and financial information.
Databases are now also used in nearly all e-commerce sites to
store product inventory and customer information. Database software,
such as Microsoft Access, FileMaker Pro, and MySQL is designed
to help companies and individuals organize large amounts of information
in a way where the data can be easily searched, sorted, and updated.
While the first databases were relatively "flat" (limited
to simple rows and columns), today's relational databases allow
users to access, update, and search information based on the
relationship of data in one database to another. Certain databases
even let users store data such as sound clips, pictures, and
Data channel: The cables
and infrastructure of a network.
Data frame: The basic
package of bits that represents the PDU sent from one computer
to another across a networking medium. In addition to it's contents
(payload), a data frame includes the sender's and receiver's
network addresses, as well as some control information at the
head and a CRC at the tail.
Data Link layer: Layer
2 in the OSI reference model. This layer is responsible for managing
access to the networking medium and for ensuring error-free delivery
of data frames from sender to receiver.
Data section: The actual
data being sent across a network. The size of this section can
vary from 512 bytes to 16 kilobytes depending on the network
Datagrade: A designation
for cabling of any kind that indicates that it's suitable for
transporting digital data. When applied to twisted-pair cabling
it indicates that the cable is suitable for either voice or data
Datagram: The term used
in some protocols to define a packet.
DBMS: "Dataase Management
System" A client/server computing environment that uses
SQL to retrieve data from the server.
DCE: "Data Communications
Equipment" Any type of device, such as a modem, that connects
a DTE to a communications line.
DDP: "Delivery Datagram
Protocol" Data transport protocol for AppleTalk.
DDR: "Double Data
Rate" It is an advanced version of SDRAM, a type of computer
memory. DDR-SDRAM, sometimes called "SDRAM II," can
transfer data twice as fast as regular SDRAM chips. This is because
DDR memory can send and receive signals twice per clock cycle.
The efficient operation of DDR-SDRAM makes the memory great for
notebook computers since it uses up less power.
DDS: "Digital Data
Service" A type of point-to-point synchronous communication
link offering 2.4-, 4.8-, 9.6- or 56-Kbps transmission rates.
DECNet: Digital Equipment
Corporation's protocol suite.
Dedicated circuit: An
ongoing (but possibly transient) link between two end systems.
Dedicated server: A network
server that acts only as a server and is not intended for regular
use as a client machine.
Default: This term is
used to describe a preset value for some option in a computer
program. It is the value used when a setting has not been specified
by the user. For example, the default font setting in Netscape
Communicator is "Times." If you don't go to the Netscape
preferences and change it to something else, the "Times"
font will be used by default. Typically, default settings are
set to what most people would choose anyway, so there's often
no reason to change them. However, if you're one of those people
who has to customize everything that you possibly can, then you
can go ahead and change all the default settings you want. "Default"
can also be used as a verb. If a custom setting won't work for
some reason, the program will "default" to the default
setting. For example, say you're working on computer that is
on a network and you print something when there is no printer
specified. If you're lucky and don't get some nasty error message,
the print job will default to the default printer and your work
will be printed.
your hard drive is a great way to boost the performance of your
computer. Though the term "defragment" sounds a little
abrasive it is actually a simple and helpful process. Adding
and deleting files from your hard drive is a common task. Unfortunately,
this process is not always done efficiently. For example, when
you delete a bunch of little files and add a new large file,
the file may get broken up into mulitple sections on the hard
drive. The computer will still read the newly added file as a
single valid file but it will have to scan multiple parts of
the drive to read it. Because hard disk seek time is one of the
biggest bottlenecks in a computer's performance this can drag
down your computer's speed quite a bit. If you have a ton of
"fragmented" files on your hard disk you might hear
extra grinding, sputtering, and other weird noises coming from
your computer. You computer doesn't like having fragmented files
any more than you do. This is why defragmenting your hard drive
is such a good idea. When you start to hear extra grinding sounds,
or your computer doesn't open files as quickly as it did before,
it's time to defragment. With Windows, you can use the pre-installed
Intel defragment program to defragment your hard drive. You can
also use a commercial software program like Norton Utilities
to defragment your hard drive more efficiently and with more
options. For Mac users Norton Utilities or another hard drive
utility is the only way to do it. If you use your computer daily,
defragmenting your hard drive once a month should keep the fragments
Degauss: Ever wonder what
that "degauss" button on your monitor does besides
make a buzzing noise and cause the screen to go crazy for a second?
Though that's its main purpose, the degauss button has another
useful feature. To understand it, you'll first need to know that
the earth has natural magnetic fields. The magnetic charges from
these fields can build up inside your monitor, causing a loss
of color accuracy. Degaussing scares the bad magnetism out of
the monitor and fills it with good karma. If your monitor doesn't
have a degauss button fear not, many new monitors automatically
degauss themselves. If you have a flat-panel (lcd) display there
is no degauss button because magnetism doesn't build up in flat
Demand priority: A high-speed
channel access method used by 100VG-AnyLAN in a star hub topology.
Demand signal: A signal
sent by a computer in a demand priority network that informas
the controlling hub it has data to send.
with drive mappings. Working in coordination with a redirector
it exchanges the locally mapped drive letter with the correct
network address of a directory share inside a resource request.
Desktop software: Sometimes
called client software or productivity applications this type
of software is what users run on their computers.
Device driver: A software
program that mediates communications between an operating system
and a specific device for the purpose of sending and/or receiving
input and output from that device.
Device sharing: A primary
purpose for networking: permitting users to share access to devices
of all kinds, including servers and peripherals such as printers
DHCP: "Dynamic Host
Configuration Protocol" A network server uses this protocol
to dynamically assign IP addresses and subnet masks to networked
computers. The DHCP server waits for a computer to connect to
it then assigns it an IP address from a master list stored on
the server. DHCP helps in setting up large networks since IP
addresses don't have to be manually assigned to each computer
on the network. Because of the slick automation involved with
DHCP it is one of the most commonly used networking protocols.
Diagnostic software: Specialized
programs that can probe and monitor a system or a specific system
component to determine if it works properly and, if not, try
to determine the cause of the problem.
Diagram: A term used to
describe a network's design.
Dial-Up Networking (DUN):
The program included with Windows 9x (95 & 98), Windows Millenium,
NT, and 2000 that allows connectivity to servers running RAS
Dictionary attack: A method
of attempting to determine an account's password by trying every
word in the dictionary for the password.
Differential backup: Copies
of all files modified since the last full backup.
Digital modem: A hardware
device used to transmit digital signals across an ISDN link.
DIP: "Dual Inline
Package" An integrated computer circuit that features two
parallel rows of pins of equal length, offset approximately 1
DIP switch: An electrical
circuit that consists of a series of individual two-way switches
contained in a single chip.
DIMM: "Dual In-Line
Memory Module" It is a type of computer memory. A DIMM is
a small circuit board that holds memory chips. It uses a 64-bit
bus to the memory, whereas a single in-line memory module (SIMM)
only has a 32-bit path. This allows DIMMs to transfer more data
at once. Because DIMMs have faster data transfer capabilities
than SIMMs they have pretty much replaced SIMMs.
The form of spread-spectrum data transmission that breaks data
into constant length segments called chips and transmits the
data on multiple frequencies.
Directory server: A specialized
server whose job is to respond to requests for specific resources,
services, users, groups and so on. This kind of server is more
commonly called a domain controller in Windows NT Server and
Windows 2000 networking environments.
Directory services: A
comprehensive network service that manages information about
network services, resources, users, groups and other objects
so that users may access resources and services by browsing for
them, or asking for them by type, along with maintaining and
enforcing access control information for directory objects.
Discovery: The process
by which dynamic routers learn the routes available to them.
Disk duplexing: A fault-tolerant
disk configuration in which data is written to two hard drives,
each with its own disk controller, so that if one disk or controller
fails the data still remains accessible.
Disk mirroring: A fault-tolerant
disk configuration in which data is written to two hard drives
rather than one so that if one disk fails the data remains accessible.
Disk striping with parity:
A fault-tolerant disk configuration in which parts of several
physical disks link together in an array and data and parity
information is written to all disks in this array. If one disk
fails then the data may be reconstructed from the parity information
written to the other disks.
Network computers that require a special type of ROM in order
to boot because they have no built-in hard drive.
One method of determining the best route available for a packet.
Distance-vector protocols count the number of routers (hops)
between the source and destination. The best path has the least
number of hops.
DIX: "Digital, Intel,
Xerox" The group that introduced the first Ethernet connector.
DLC: "Data Link Control"
A network protocol used mainly by Hewlett-Packard printers and
IBM mainframes attached to a network.
DLL: "Dynamic Link
Library" A DLL (.dll) file contains a library of functions
and other information that can be accessed by a Windows program.
When a program is launched links to the necessary .dll files
are created. If a static link is created the .dll files will
be in use as long as the program is active. If a dynamic link
is created the .dll files will only be used when needed. Dynamic
links help programs use resources, such as memory and hard drive
space, more efficiently. DLL files can also be used by more than
one program. In fact, they can even be used by multiple programs
at the same time. Some DLLs come with the Windows operating system
while others are added when new programs are installed. You typically
don't want to open a .dll file directly, since the program that
uses it will automatically load it if needed. Though DLL filenames
usally end in ".dll," they can also end in .exe, .drv,
DMA: "Direct Memory
Access" A technique for addressing memory on some other
device as if it were local memory directly available to the device
accessing the memory. The technique lets a CPU
gain immediate access to the buffers on any NIC
that supports DMA.
DNS: "Domain Name
System" The primary purpose of DNS is to keep Web surfers
sane. Without DNS, we would have to remember the IP address of
every site we wanted to visit, instead of just the domain name.
Can you imagine having to remember "188.8.131.52" instead
of just "apple.com"? While I have some Computer Science
friends who might prefer this, most people have an easier time
remembering simple names. The reason the Domain Name System is
used is because Web sites are acutally located by their IP addresses.
For example, when you type in "http://www.adobe.com,"
the computer doesn't immediately know that it should look for
Adobe's web site. Instead, it sends a request to the nearest
DNS server, which finds the correct IP address for "adobe.com."
Your computer then attempts to connect to the server with that
Domain: A uniquely named
collection of user accounts and resources that share a common
Domain controller: On
networks based on Windows NT Server or Windows 2000 Server a
directory server that also provides access controls over users,
accounts, groups, computers and other network resources.
Domain model: A network
based on Windows NT Server or Windows 2000 Server whose security
and access controls reside in a domain controller.
Domain Name: This is the
name that identifies a web site. For example, "microsoft.com"
is the domain name of Microsoft's web site. A single web server
can serve web sites for multiple domain names but a single domain
name can point to only one machine. For example, Apple Computer
has web sites at www.apple.com, www.info.apple.com, and store.apple.com.
Each of these sites could be served on different machines. Then
there are domain names that have been registered but are not
connected to a web server. The most common reason for this is
to have e-mail addresses at a certain domain name without having
to maintain a web site. In these cases the domain name must
be connected to a machine that is running a mail server. Another
popular use for multiple domain names is to use forwarding & masking
to redirect one domain name to another. A domain name works like an
address forwarding service. All of your Web site content sits on a
computer with a unique address. This is called an IP address. An IP
address is made up of a series of numbers, such as 184.108.40.206.
Your domain name directs visitors to your site using this IP address.
We use domain names instead of IP addresses because most people find
it easier to remember a name rather than a series of numbers.
Dongle: This computer
term has two different meanings:
1. A security key. This is a little hardware device that plugs
into the serial or USB port of a computer. Its purpose is to
ensure that only authorized users can use certain software applications.
If you have never seen a dongle, don't be surprised. They are
only used with expensive, high-end software programs that most
people have never heard of, much less use. When a program that
comes with a dongle runs, it checks the dongle for verification
as it is loading. If it doesn't find the dongle, the computer
execute the program. If more than one application requires a
dongle, multiple dongles using the same port can be daisy-chained
2. A laptop Ethernet card adapter. This is a little connector
that attaches to a PC card in a laptop on one end, and to an
Ethernet cable on the other end. Since most PC (or PCMCIA) network
interface cards are too small to connect directly to a standard
RJ-45 Ethernet cable, they need this little adapter that connects
the card to the cable. (3Com cards that use an "X-Jack"
connector do not need a dongle.)
Dot Pitch: This is the
measurement used to determine how sharp the display of a CRT
(Cathode Ray Tube) monitor is. It is measured in millimeters
and the smaller the number the finer the picture. Most CRT monitors
will have a dot pitch between .25 and .28. However, some large
presentation monitors have dot pitches from .30 to .50 (which
would make for really fuzzy images on a standard 17" desktop
monitor). The difference between a "dot" (as in dot
pitch) and a pixel is that a pixel is mapped onto the dots on
the screen. When the monitor is set to lower resolutions, one
pixel encompasses multiple dots. So pixels are typically larger
than the "dots" on the actual screen. In a CRT display
with a shadow mask, the dot pitch is measured as the distance
between the holes of the shadow mask, again in millimeters. "So
what's a shadow mask?" you ask. It's basically a metal screen
full of holes where three electron beams (red, green, and blue)
pass through. These beams focus to a single point on the tube's
phosphor surface. Thousands of these points make up the images
on your screen. In a CRT display that uses an aperture grill
(like a Sony Trinitron monitor), the dot pitch is measured by
the distance between adjacent slots where electron beams of the
same color pass through.
Download: This is the
process in which data is sent to your computer. Whenever you
receive information from the Internet you are downloading it
to your computer. For example, you might have to download an
upgrade for your computer's operating system in order to play
a new game (especially if you're using Windows). Or you might
download a demo version of a program you are thinking about buying
from the software company's web site. The opposite of this process,
sending information to another computer, is called uploading.
Drive mapping: The convention
of associating a local drive letter with a network directory
share to simplify access to the remote resource.
Driver: In the computer
world a driver is a small file that helps the computer communicate
with a certain hardware device. It contains information the computer
needs to recognize and control the device. In Windows-based PCs
a driver is often packaged as a dynamic link library, or .dll
file. In Macs most hardware devices don't need drivers, but the
ones that do usually come with a software driver in the form
of a system extension, or .kext file.
DS: A specification level
for DDS lines. A T1 is a DS-1 or 1.544 Mbps; a single channel
fractional T1 is a DS-0 or 64 Kbps.
DSL: "Digital Subscriber
Line" It is another medium for sending data over regular
phone lines and connecting to the Internet. However, like a cable
modem, a DSL circuit is much faster than a regular phone connection,
even though the wires it uses are copper like your typical phone
line. An asymmetric DSL (ADSL) connection allows download speeds
of up to about 1.5 megabits (not megabytes) per second, and upload
speeds of 128-384 kilobits per second. That is why it is called
aDSL and not just DSL (because of the asymmetric speeds). There
is also a "Symmetric Digital Subscriber Line" (sDSL)
which is similar to aDSL, but allows data transfer speeds of
384 Kilobits per second in both directions. Theoretically, this
type of connection allows download speeds of up to 9 megabits
per second and upload speeds of up to 640 kilobits per second.
The difficult part in establishing an DSL circuit is that it
must be configured to connect two specific locations, unlike
a regular phone line or cable modem. DSL is often seen as the
new, better alternative to the older ISDN standard.
DTE: "Data Terminal
Equipment" Any device that transmits digital information
over a communications line.
DVD: "Digital Versatile
Disc" It can also stand for "Digital Video Disc,"
but with the mulitple uses of DVDs, the term "Digital Versatile
Disc" is more correct. A DVD is a high-capacity optical
disc that looks like a CD, but can store much more information.
While a CD can store 650 to 700 MB of data, a single-layer, single-sided
DVD can store 4.7 GB of data. This enables massive computer applications
and full-length movies to be stored on a single DVD. The advanced
DVD formats are even more amazing. There is a two-layer standard
that doubles the single-sided capacity to 8.5 GB. These disks
can also be double-sided, ramping up the maximum storage on a
single disc to 17 GB. That's 26 times more data than a CD can
hold. To be able to read DVDs in your computer you'll need a
DVD-ROM drive. Fortunately, DVD players can also read CDs. To
play DVD movies on your computer you'll need to have a graphics
card with a DVD-decoder which most computers now have.
DVI: "Digital Video
Interface" It is a video connection standard created by
the Digital Display Working Group (DDWG). Most DVI ports support
both analog and digital displays. If the display is analog, the
DVI connection converts the digital signal to an analog signal.
If the display is digital, no conversion is necessary. There
are three types of DVI connections: 1) DVI-A (for analog), 2)
DVI-D (for digital), and 3) DVI-I (integrated, for both analog
and digital). The digital video interface supports high bandwidth
signals, over 160 MHz, which means it can be used for high resolution
displays such as UXGA and HDTV. You may find DVI ports on video
cards in computers as well as on high-end televisions.
DVM: "Digital Voltmeter"
A network troubleshooting tool that measures voltage, amperage
and resistance on a cable or other conductive element.
Dynamic routing: The process
by which routers dynamically learn from each other the available
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