Refers to the transmission of data in just one direction at a time. For
example, a walkie-talkie is a half-duplex device because only one party can
talk at a time. In contrast, a telephone is a full-duplex device because
both parties can talk simultaneously.
Most modems contain a switch that lets you select between half-duplex and
full-duplex modes. The correct choice depends on which program you are using
to transmit data through the modem.
In half-duplex mode, each character transmitted is immediately displayed on
your screen. (For this reason, it is sometimes called local echo --
characters are echoed by the local device). In full-duplex mode, transmitted
data is not displayed on your monitor until it has been received and
returned (remotely echoed) by the other device. If you are running a
communications program and every character appears twice, it probably means
that your modem is in half-duplex mode when it should be in full-duplex
mode, and every character is being both locally and remotely echoed.
The process by which two devices initiate communications. Handshaking
begins when one device sends a message to another device indicating that it
wants to establish a communications channel. The two devices then send
several messages back and forth that enable them to agree on a
A hard reboot (also known as a cold reboot) is when power to a computer
is cycled (turned on and off) or a special reset signal to the processor is
triggered (from a front panel switch of some sort). This restarts the
computer without first performing the usual shut-down procedure. (With many
operating systems, especially those with disc caches, after a hard reboot
the system may well be in an "unclean" state, and require that checks and
repairs to on-disc filesystem structures be performed before normal
operation can begin.) It may be caused by power failure, be done by
accident, or be done deliberately as a last resort because nothing else to
retrieve the system from a "hung" state works.
These are the physical items including your computer and floppy discs.
Hayes Microcomputer Products is one of the leading manufacturers of
modems and has developed a language called the AT command set for
controlling modems that has become the de facto standard. Any modem that
recognizes Hayes modem commands is said to be Hayes-compatible.
This is very useful because most communications programs use Hayes modem
commands. Virtually all modems manufactured today are Hayes-compatible.
Central distribution point for a CATV system. Video signals are received
here from satellites and maybe other sources, frequency converted to the
appropriate channels, combined with locally originated signals, and
rebroadcast onto the HFC plant. The headend is where the CMTS is normally
A component designed to lower the temperature of an electronic device by
dissipating heat into the surrounding air. All modern CPUs require a heat
sink. Some also require a fan. A heat sink without a fan is called a passive
heat sink; a heat sink with a fan is called an active heat sink. Heat sinks
are generally made of a zinc alloy and often have fins.
This is an application your browser uses to manipulate a downloaded
Hybrid fiber-coaxial (cable network). Older CATV systems were
provisioned using only coaxial cable. Modern systems use fiber transport
from the headend to an optical node located in the neighborhood to reduce
system noise. Coaxial cable runs from the node to the subscriber. The fiber
plant is generally a star configuration with all optical node fibers
terminating at a headend. The coaxial cable part of the system is generally
a trunk-and-branch configuration.
In DOS -based systems, the high memory area refers to the first 64K of
High Speed Technology- Before the invention of the CCITT V.32 modem
standards for 9600 BPS modems, US Robotics invented a proprietary protocol
that runs even faster at 14,400 BPS. It became popular on US bulletin board
system, but never caught on outside the USA. It is gradually being replaced
A computer on a network that provides services to other computers on the
network. Unless you have your own server, you need a hosting company who
provides a server or computer that is connected to the internet and makes
your web pages available to the rest of the internet.
Novell, Inc.'s term for the feature of their network file server
operating system, Novell NetWare, which handles errors in disk write
operations. The OS re-reads every block it writes to disk while it holds the
data to be written in memory. In the case of an error, the data block is
written to a spare area on the disk.
The feature lost much of its importance with the widespread use of hard disk
drives with built-in error correction and bad block re-mapping.
List of URLs saved within the Mosaic Web browser. (Bookmark in
This refers to a device that is designed to be removed or replaced while a
system is turned on without disturbing the computers function. A good
example of a hot swappable device is the USB flash drive.
Hyper Text Markup Language. It is a collection of structuring and
formatting tags used to create Web pages.
Stands for HyperText Transport Protocol. Common protocol used to
communicate between World Wide Web Servers.
A common connection point for devices in a network. Hubs are commonly
used to connect segments of a LAN. A hub contains multiple ports. When a
packet arrives at one port, it is copied to the other ports so that all
segments of the LAN can see all packets.
A passive hub serves simply as a conduit for the data, enabling it to go
from one device (or segment) to another. So-called intelligent hubs include
additional features that enables an administrator to monitor the traffic
passing through the hub and to configure each port in the hub. Intelligent
hubs are also called manageable hubs.
A third type of hub, called a switching hub, actually reads the destination
address of each packet and then forwards the packet to the correct port.
A device or system combining two types of mechanisms, circuits, or
design approaches, each of which could of itself accomplish the total
function but in a different and usually less effective manner. A hybrid
computer combines digital and analog computers into one functioning system.
This is a mark-up language that allows for non-linear transfers of data.
The method allows your computer to provide the computational power rather
than attaching to a mainframe and waiting for it to do the work for you.
(HTT = Hyper Threading Technology) is Intel's trademark for their
implementation of the simultaneous multithreading technology on the Pentium
4 microarchitecture. It is basically a more advanced form of Super-threading
that first debuted on the Intel Xeon processors and later added to Pentium 4