H

• Half-Duplex:
  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.
   

• Handshaking:
  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 communications protocol.
   

• Hard Boot:
  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.
   

• Hardware:
  These are the physical items including your computer and floppy discs.
   

• Hayes Compatible:
  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.
   

• Headend:
  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 located.
   

• Heat Sink:
  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.
   

• Helper Application: 
  This is an application your browser uses to manipulate a downloaded program.
   

• HFC:
  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.
   

• High Memory Area:
  In DOS -based systems, the high memory area refers to the first 64K of extended memory.
   

• HST:
  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 by V.32.
   

• Host:
  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. 
   

• Hot Fix:
  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.
   

• Hotlist: 
  List of URLs saved within the Mosaic Web browser. (Bookmark in Netscape.)
   

• Hot Swappable:
  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.
   

• HTML: 
  Hyper Text Markup Language. It is a collection of structuring and formatting tags used to create Web pages.
   

• HTTP: 
  Stands for HyperText Transport Protocol. Common protocol used to communicate between World Wide Web Servers.
   

• Hub:
  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.
   

• Hybrid:
  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. 
   

• Hypertext: 
  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.
   

• Hyper-Threading:
  (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 processors.  

H