H

H is for Hacker

Hack: Any software in which a significant portion of the code was originally another program.

Hacker: Those intent upon entering an environment to which they are not entitled entry for whatever purpose. Usually iterative techniques escalating to more advanced methodologies and use of devices to intercept the communications property of another. See also Cracker.

Half Duplex Mode: A data communications term that indicates that only one end of a communications link can transmit data at the same time; one end must wait for acknowledgement of its data transmission from the other end before it can continue transmitting another data packet. See also Full Duplex Mode.

Hamming Code: A method that adds redundant bits to a data unit to detect and correct bit errors.

Hayes-Compatible Modems: An intelligent modem capable of more than just modulation and demodulation.

HDLC (High level Data Link Control): A bit oriented data link protocol defined by the ISO. It is used in the X.25 protocol. A subset, called link access procedure (LAP), is used in other protocols. It is also a base for many data link protocols used in LANs.

HDSL: High bit rate Digital Subscriber Line (HDSL) is a bidirectional and symmetrical transmission system that allows the transport of signals with a bit rate of 1.544 Mbps or 2.048 Mbps on the twisted pairs of an access network.. It can be used without amplification up to 3.6 Km. ITU-T recommendation G.991.1. See also xDSL.

Header: The portion of a packet, proceeding the actual data, containing source and destination addresses and error-checking fields.

Helper Applications: Additional software occasionally needed to help a Web browser program deal with a file on the Internet. When the file is downloaded, a helper application takes over for the Web browser to open and run the file. An example of a helper application is the Real Player. It opens and plays Real audio/video files when they are encountered on the Internet.

High Voltage - Voltages 750, 400 or 220 kV.

High-Frequency Voltage Factor - Ratio of the square root of the sum square of the rms values of the higher order harmonic contents to the rms value of the first harmonic.

Hit: A hit has come to mean many things and is possibly one of the most misleading terms used among web sites. Technically, a hit is counted for each file transferred from the web server to the web browser and has led to many exaggerated claims on web sites. This is because if a web page has 5 graphics on it, it counts as 6 hits; one for the web page itself and 5 for each of the graphics. Unfortunately, hits has been misleadingly used to refer to the number of times a particular web page has been loaded so that a person thinks the site has been visited 6 times by 6 people when it was only visited once.

Home Page: Originally it referred to the web page that was loaded when a web browser was first launched. It also refers to the primary web page for a web site.

Honeypot: Honeypots are programs that simulate one or more network services that you designate on your computer's ports. An attacker assumes you're running vulnerable services that can be used to break into the machine. A honeypot can be used to log access attempts to those ports including the attacker's keystrokes. This could give you advanced warning of a more concerted attack. Honeypots are most successful when run on well-know servers, such as Web, mail, or DNS servers because these systems are often attacked. They can also be used when a system comes under attack by substituting a honeypot system for the target.

Host: Any computer (node) connected to a network which is directly used by resources (e.g., public domain programs, text/data files, mailboxes, etc.). An Internet host can be identified by its dotted quad address or its distinctive domain name. This computer system may also be the source of network services on which you may hold an interactive session if you are a valid user of that system.

Host-based Security: The technique of securing an individual system from attack. Host-based security is operating system and version dependent.

Hostname: The name given to a computer; PC, workstation or server.

Hot Standby: A backup system configured in such a way that it may be used if the system goes down.

Hourly reserve - Mean hourly available capacity of thermal running generating unit, reduced by its actual load, second and minute reserve volume or available capacity of generating unit that is not in operation being able to start-up and synchronization with the grid within time no longer than 30 min.

HTML (HyperText Markup Language): The computer “language” of the World Wide Web, comprised of the coding, or tags, that indicate how text and images are to be displayed, as well as how documents and files are to be linked. HTML was developed at CERN. It is based on SGML.

HTTP (HyperText Transport Protocol): HTTP is an application-level protocol with the lightness and speed necessary for distributed, collaborative, hypermedia information systems. HTTP has been in use by the World-Wide Web global information initiative since 1990. Secure HTTP (S-HTTP) is a secure message-oriented communications protocol designed for use in conjunction with HTTP. It is designed to coexist with HTTP's messaging model. HTTPS is HTTP encapsulated in an SSL/TLS stream. HTTP v1.1 is defined in RFC 2616 and RFC 2617, with updates in RFC 2817.

Hub: (1) A local network device. Either a repeater or a bridge. (2) A regional point of connection between an Internet user and the Internet. Regional hubs are also called ISPs, which sell their networking services for a fee.

Hyperlink: A reference in an HTML document that leads to a separate document or media file and allows the reader to follow non-linear information trails through HTML documents. Although primarily a computer based concept, some have tried to create printed books based upon hyperlinks/hypertext.

Hypertext: Any text that contains links (hyperlinks) to other text in the same document or other documents. The World Wide Web is based upon hypertext but is not the only example of hypertext. Many help systems on computers are based upon hypertext. One of the first commercial programs using hypertext was Apple's HyperCard.

HYTELNET: Program that provides flexible connection to a variety of networked information resources including online public access catalogs.