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Data Service Unit (DSU). <I>See also</I> CSU and DSU.</P>
<P><B>DEBNA  </B>Digital Ethernet VAXBI Network Adapter. Replaced by the
DEBNI. <I>See</I> DEBNI.</P>
<P><B>DEBNI  </B>Digital Ethernet VAXBI Network Interface. A DEC controller
card for VAX computers that interfaces the VAXBI bus with the Ethernet LAN. The DEBNI
replaced the DEBNA. <I>See</I> DEBNA.</P>
<P><B>DEC  </B>Digital Equipment Corporation.</P>
<P><B>DECmate  </B>An office automation (word processing) microcomputer.</P>
<P><B>DECnet  </B>Digital's line of products that allow communications
between DEC systems.</P>
<P><B>DECnet-DOS  </B>A DEC software product for PCs and PS/2s running
MS- DOS (or PC-DOS). DECnet-DOS enables the PC to participate in a DECnet network
(normally through a Ethernet adapter in the PC). The functions provided by DECnet-DOS
include task-to-task communications, remote file access and VT 220 terminal emulation.</P>
<P><B>DECnet/SNA Gateway  </B>A LAN-attached gateway between SNA and DECnet.
The IBM side of the gateway might attach via an SNA SDLC connection or via a direct
channel attachment to a mainframe. Specific SNA services are run in other DEC hosts
to provide functional services across the gateway (such as terminal access, file
transfer and document exchange). <I>See</I> gateway.</P>
<P><B>DECrouter  </B>LAN-attached bridges to facilitate wide-area connections
within DECnet networks. A router can be used to connect two Ethernet LANs using DDCMP
or X.25. A router on one LAN can communicate with another router or with an integrated
communications card within a DEC host system.</P>
<P><B>DECserver  </B>Digital's LAN terminal server. <I>See</I> terminal
server.</P>
<P><B>DECstation  </B>Digital's line of PCs based on Intel processors and
their line of engineering workstations based on RISC technology. The DECstation 3100
and 5000 use a RISC design while the DECstation 200, 300, and 400 models use standard
PC architectures. <I>See also</I> VAXstation.</P>
<P><B>DECwindows  </B>DEC's architecture for a graphical user interface
that provides a common, multiwindowed graphical environment from which the end user
can access applications residing on other systems. DECwindows is part of DEC's Network
Application Support (NAS). <I>See also</I> NAS.</P>
<P><B>DELNI  </B>Digital Ethernet Local Network Interconnect. Provides
connection to eight Ethernet segments with a ninth connection that can be used to
optionally attach the DELNI to the LAN backbone. The DELNI can be used as a stand-alone
device to create a small DECnet network, or can be networked into a main LAN as described.</P>
<P><B>DELQA  </B>Digital Ethernet LAN-Q-bus Adapter. A DEC controller card
for Q-bus computers that interfaces the computer with the Ethernet LAN. The DELQA
replaces the DEQNA.</P>
<P><B>DELUA  </B>Digital Ethernet LAN-Unibus Adapter. A DEC controller
card for Unibus computers that interfaces the computer with the Ethernet LAN. The
DELUA replaces the DEUNA.</P>
<P><B>DEMCA  </B>Digital Ethernet MicroChannel Adapter. An Ethernet ThinWire
adapter card for PS/2 computers. DEMCA uses a standard MCA slot.</P>
<P><B>DEMPR  </B>Digital Ethernet Multi-Point Repeater. A DEC LAN product
that provides eight ThinWire ports, with a ninth port to optionally connect to the
standard Ethernet cable. Like a DELNI, a DEMPR can be used to implement a standalone
ThinWire LAN or to integrate ThinWire devices into a main Ethernet LAN.</P>
<P><B>DEPCA  </B>Digital Ethernet PC Adapter. An Ethernet ThinWire adapter
card for PCs. DEPCA uses a standard 8-bit PC slot.</P>
<P><B>DEQNA  </B>Digital Ethernet Q-bus Network Adapter. The DEQNA was
replaced by the DELQA. <I>See</I> DELQA.</P>
<P><B>DeskManager  </B>HP's electronic mail and office automation product
for the HP 3000 computer.</P>
<P><B>DESPR  </B>Digital Ethernet Single-Port Repeater. A DESPR provides
conversion between an Ethernet transceiver connection and a ThinWire connection.
A DESPR is used to attach a ThinWire device to a standard Ethernet transceiver. <I>See
also</I> DESTA.</P>
<P><B>DESTA  </B>Digital Ethernet Station Adapter. A DESTA provides conversion
between a ThinWire connection and an Ethernet transceiver. A DESTA is used to attach
a standard Ethernet device into a ThinWire network. <I>See also</I> DESPR.</P>
<P><B>DESVA  </B>Digital Ethernet MicroVAX 2000 Adapter. A DEC controller
card for the MicroVAX 2000 that interfaces the computer with the Ethernet LAN.</P>
<P><B>DEUNA  </B>Digital Ethernet Unibus Network Adapter. The DEUNA was
replaced by the DELUA. <I>See</I> DELUA.</P>
<P><B>DHCF  </B>Distributed Host Command Facility. An IBM product running
as a remote processor, DHCF interfaces with the mainframe-resident HCF subsystem
to provide distributed access. In a pure IBM environment, it is often used to gain
3270 terminal access from a mainframe to a remote, nonmainframe system. In the multivendor
arena, DHCF is often emulated to allow 3270 terminals to access the non-IBM system
via the mainframe HCF facility.</P>
<P><B>DIA  </B>Document Interchange Architecture. One of three distribution
techniques used by IBM to move information from system to system in an SNA network.
DIA is specifically focused on the movement of documents in both revisable and final
form. <I>See also</I> DCA, DDM and SNADS.</P>
<P><B>digital transmission.</B> Transmission in which information is sent in its
discrete bit form. That is, each bit is represented as a 0 or a 1. <I>See also</I>
analog transmission.</P>
<P><B>DISOSS  </B>Distributed Office Support System. An IBM product that
enables documents created by different products to be distributed and shared among
IBM systems. DISOSS is commonly used as an interface point for transmitting documents
to and from non-IBM computers.</P>
<P><B>DMA  </B>Direct Memory Access. A hardware method of reading and writing
directly to memory without involving the main CPU.</P>
<P><B>DNA  </B>Digital Network Architecture. DEC's architecture for the
interconnection of its computer and computer-related devices. This is equivalent
to IBM's SNA, HP's AdvanceNet, and Sun's ONC.</P>
<P><B>DoD  </B>U.S. Department of Defense. <I>See also</I> DARPA.</P>
<P><B>Domain  1.</B> A set of hosts on a LAN that share a single database,
typically for moving mail between hosts. <B>2.</B> The name for Apollo's (now HP's)
line of engineering workstations. <I>See also</I> Apollo.</P>
<P><B>DOS  </B>Disk Operating System. Introduced in 1981 by Microsoft Corp.
as the operating system for IBM's 8080-based IBM PC.</P>
<P><B>DOS/VS  </B>Disk Operating System/Virtual Storage. An IBM System/370
architecture operating system.</P>
<P><B>DOS/VSE  </B>Disk Operating System/Virtual Storage Extended. An IBM
System/370 architecture operating system.</P>
<P><B>dpi  </B>Dots per inch. A term used to describe the resolution of
printers. Most dot-matrix printers offer less than 200 dots per inch resolution,
while most laser or inkjet printers offer at least 300 and as high as 1,200 dots
per inch. The higher the density of dots, the better the resolution of printed characters,
graphics and images. In contrast, typesetting equipment can offer dpi resolution
of 1,270, 2,540, and even higher amounts.</P>
<P><B>DS/1000 and DS/3000  </B>HP 1000 and HP 3000 networking services
that have been replaced by NS/1000 and NS/3000. The DS services relied mostly on
HP HDLC links for networking, while the NS products use standard IEEE 802.3 links.</P>
<P><B>DS0  </B>Digital Service rate 0. The transmission rate (64 Kbps)
of each of the 24 circuits in a T1 connection. <I>See also</I> T1.</P>
<P><B>DS1  </B>Digital Service rate 1. The combined transmission rate (1.544
Mbps) of all 24 circuits in a T1 connections. <I>See also</I> T1.</P>
<P><B>DSM-11  </B>DEC's business-oriented operating system for the PDP/11
series computers. <I>See also</I> CTS-300, RSTS, and RSX.</P>
<P><B>DSR  </B>Data Set Ready. A lead in the RS-232C interface, DSR is
used to signal that the modem (or DCE device) is ready for communications. The counterpart
to DSR is Data Terminal Ready (DTR), which is the computer/terminal's signal that
it is ready to communicate. In most cases, no communication can take place unless
both the DSR and DTR signals are raised. In the full 25-pin RS-232C standard, DSR
is pin 6. In the abbreviated, 9-pin PC interface, DSR is pin 4. <I>See also</I> DTR
and RS-232C.</P>
<P><B>DSU  </B>Data service unit. A device that interfaces between a channel
service unit (CSU) and a terminal or computer. The DSU and CSU work together to interface
the computing device to a digital data service (DDS). <I>See also</I> CSU, DDS, and
ISU.</P>
<P><B>DTC  </B>Distributed terminal controller. For the RISC-based HP 3000
systems, DTCs are used to interface the asynchronous terminals into the LAN-based
system. <I>See also</I> ADCC and ATP.</P>
<P><B>DTE  </B>Data terminal equipment. A device such as a terminal or
computer that is the origin or destination of information flowing over a data communications
link. The DTE interfaces with data communication equipment such as a modem, that
handles the actual data communications processing and interfaces with another DCE
device (that interfaces with another DTE device). When direct connect links are used,
one side emulates a DCE while the other performs normal DTE functions. <I>See also</I>
DCE.</P>
<P><B>DTP  </B>Distributed Transaction Processing. An OSI upper-layer service
for implementing transaction-based processing. Defined as ISO standard 10026.</P>
<P><B>DTR  </B>Data Terminal Ready. A lead in the RS-232C interface. Data
Terminal Ready is used to signal to the modem (or DCE device) that it is ready for
communications. The counterpart to DTR is Data Set Ready (DSR), which is the modem's
signal that it is ready to communicate. In most cases, no communication can take
place unless both the DTR and DSR signals are raised. In in-dial situations, DTR
is normally raised when the Ring Indicator (RI) is raised to tell the modem to answer
the phone. In the full 25-pin RS-232C standard, DTR is pin 20. In the abbreviated,
9-pin PC interface, DTR is pin 4. <I>See also</I> DSR, RI, and RS-232C.</P>
<P><B>Duplex  </B><I>See</I> half duplex and full duplex.
<H2><A NAME="Heading6"></A><FONT COLOR="#000077">E</FONT></H2>
<P><B>EBCDIC  </B>Extended Binary Coded Decimal Interchange Code. A definition
for the bit compositions of characters and symbols. EBCDIC uses 256 eight-bit patterns
to define 256 different characters, numbers and symbols. IBM mid-range and mainframe
systems use the EBCDIC standard. <I>See also</I> ASCII.</P>
<P><B>ECMA  </B>European Computer Manufacturers Association. A standards
organization composed of European computer manufacturers. ECMA participates in both
CCITT and ISO activities.</P>
<P><B>ECMA 40  </B>ECMA specifications for HDLC frame structure. <I>See
also</I> HDLC.</P>
<P><B>ECMA 49  </B>ECMA definition of HDLC elements of procedures. <I>See
also</I> HDLC.</P>
<P><B>ECMA 60  </B>ECMA definition of HDLC unbalanced class of procedures.
<I>See also</I> HDLC.</P>
<P><B>ECMA 61  </B>ECMA definition of HDLC balanced class of procedures.
<I>See also</I> HDLC.</P>
<P><B>ECMA 71  </B>ECMA standard for transport protocol (for ISO/OSI layer
4).</P>
<P><B>ECMA 80-82  </B>ECMA definitions of the physical and logical link
control for CSMA/CD. <I>See also</I> CSMA/CD.</P>
<P><B>EDI  </B>Electronic data interchange. A set of services for information
and document exchange. The intent of EDI is to reduce or eliminate paper flow for
common business transactions.</P>
<P><B>EIA  </B>Electronic Industries Association. A U.S. trade organization
specializing in the electrical and functional characteristics of interface equipment.
EIA has a close working relationship with ANSI.</P>
<P><B>EISA  </B>Extended Industry Standard Architecture. An alternative
to IBM's MCA bus structure for the PS/2. EISA was developed by a group of nine manufacturers
led by Compaq Computer. <I>See also</I> MCA.</P>
<P><B>EMA  </B>Enterprise Management Architecture. DEC's products and services
that implement network management.</P>
<P><B>EMI  </B>Electromagnetic Interference. Electromagnetic waves that
can potentially interfere with the operation of electronic devices. The U.S. Federal
Communication Commission (FCC) is responsible for deciding whether an electronic
device (such as a computer) generates too much EMI or radio frequency interference
(RFI). <I>See also</I> FCC and RFI.</P>
<P><B>end node</B> A node in a network that cannot forward or reroute packets intended
for other nodes. <I>See also</I> node.</P>
<P><B>ESDI  </B>Enhanced Small Device Interface. A disk interface standard
that offers storage of 34 sectors per cylinder. Because of its speed and density,
ESDI is used in both PCs and mid-range systems. <I>See also</I> MFM, RLL, SCSI, and
ST506.</P>
<P><B>Ethernet  </B>A LAN standard that uses the Carrier Sense, Multiple
Access with Collision Detection (CSMA/CD) discipline. Ethernet was originally developed
by Xerox Corporation. <I>See also</I> IEEE 802.3.</P>
<P><B>EU  </B>End User. An IBM SNA term.
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