Fiber Optics Illustrated Dictionary lTU-T G Series Recommendations, cont. General andmisceUaneous,cont. G.411 1988 0.431 1988 0.451 1988 0.702 1988 0.703 1991 G.704 1995 0.707 1996 0.722 1988 0.761 1988 0.762 1988 0.765 1992 0.766 1996 0.772 1993 G.795 1988 G.796 1992 0.921 1988 G.931 1988 0.941 1988 0.950 1988 0.951 1988 0.955 1996 G.960 1993 0.962 1993 0.963 1993 G.964 1994 G.965 1995 0.851.11996 Managementofth~transport network 0.852.11996 Managemelltofthetransport network G.853.11996 Common elements of the information viewpoint for the management of a transport network 0.853.21996 Subnetwork connection management information viewpoint G.854.11996 Management of the transport network 0.861 • ·.1996 Pripciplesand guidelioes.for the integration of satellite and radio systems in SDH transport networks G.901 1988 General considerations on digital sections and digital.line systems 0.902 1995 Framework recommendation on functional access networks (AN) architecture and functions, access types, management, and service node aspects Digital sections based on the 2048 kbps hierarchy Digital line sections at 3152 kbps Digital line systems provided by FDM transmission bearers General considerations on digital line systems Digital line systems based on the 1544 kbps hierarchy on symmetric pair cables 0.952 1988 Digital line· systems based on the 2048 bps hierarchy on symmetric pair cables 0.953 1988 Digital line systems based on the 1544 .1.<bps hierarchy OIl co· axial pair cables 0.954« 1988 DigitallinesystelP-Sbased on the 2048 kbps hierarchy on coaxial pair cables Digital line systems based on the 1544 kbps and the2048kbps hierarchy on optical fibre cables Access digital section for ISDN basic rate access Access digital section for ISDN primary rate at 2048 kbps Access digital section for ISDN primary rate at 1544 kbps V- Interfaces at the digital10cal exchange (LE) •• . • v~ Interfaces at the digital local e]tchange (LE) G.241 1988 Pilots on groups, sup~rgroups, etc. G.242 1988 . Through-connection of groups, supergroups, etc. 0.243 1988 Protection of pilots and additional· measuring frequencies at points where there is a through-connection Use of radio-relay systems for international telephone circuits Hypothetical· reference circuits for frequency-division multiplex (FIlM)radio-relay systems Use of radio links in futemational telephone circuits Digitalhierarchybit rates . PhysicaVelectrical characteristics of hierarchical digital interfaces Synchronous frame structures used at 1544, 6312, 2048, 8488, and 44,736 kbpshierarchical levels G.706 1991 Frame alignment and cyclic redundancy check (CGC) procedures relating tobasic frame structures defined in Recommendation··G.704 Network node interface for the synchronous digital hierarchy 7-kF(z audio-coding within 64 kbps General characteristics of a 60- channel transcoder equipment Oeneral characteristics of a48- channel transcoder equipment Pac~tcircuit multiplication . equipment FacsimiledemodulationJ remodulation for digital circuit multiplication·cquipment Protected monitoring points provided on digital transmission systems Characteristics of cadecs for FDM assemblies Characteristics of a 64-kbps cross- connect equipment with 2048 kbpsaccess ports 0.804 .1993 ATM. cc:lltn8pping jot() plesiochronous digital hierarchy (FllID 0.805 ·1995 Genericftmctional architecture of transport netwt}rks 432 © 2003 by CRC Press LLC b 1. abbrev. hecto See hecto 2. abbrev. horizon- tal. 3. symb. horizontal linear polarization (lTV). H bend, H-plane bend A smooth transition in the orientation of the axis of an electromagnetic waveguide such that the axis remains parallel to the direction of the magnetic H-field polarization (trans- verse polarization). The Hfields become distorted in awaveguide with an H bend. The degree of bend de- pends upon the frequency of the wave guided through the bend. The radius must exceed two wavelengths to prevent unwanted reflections. H-bend rectangular elbows for radiowave communi- cations typically have 90-degree bends with specific- sized openings through the flanges into the elbow. These are available to support a number of frequen- cies, including S-band and L-band (radar) commu- nications. H channel An lTU-T-defined transmission channel on packet-switched networks consisting of aggre- gated B channels (bearer channels), as are used on an ISDN system. See ISDN. H drive In analog video, a periodic signal related to the horizontal component of a frame that is con- structed with sequential, repeating line scans. The relationship between horizontal sync and vertical sync is such that the pulses can be combined on a single wire. Together they comprise a composite video signal. The H drive sends a short horizontal sync pulse during the horizontal blanking interval when the beam moves from right to left without trac- ing a line on the screen. A composite signal can be represented as Csync-red-green-blue and transmitted over four wires. Many computer monitors use a five- wire RGBHV system in which the H and V repre- sent horizontal and vertical sync pulse components. See negative-going video. H-plane bend See H bend. HO Channel In ATM networking, a 384-Kbps chan- nel consisting of six contiguous OS-Os (64 Kbps) of aT1transmission line. back v. 1. To quickly cobble together a program. 2. To create something quickly from available materials, a make-do solution, not necessarily elegant, although it could be, given limited resources. 3. To create a small, quick entertaining showpiece designed to il- lustrate a cool idea or interesting capability. See Schwabbie. 4. To seek to compromise or enter an area/process for which the person does not have au- thorization. hack into To find a means of entrance other than the normal way, to compromise the security ofa system by exploiting aweakness or lesser-known character- istic, to deliberately break into a computer system, network, or computer process without authorization. backer 1. A person who hacks into a system, Le., gains entry by exploiting the hardware or software architecture through black boxes, stolen or guessed passwords, Troj an horses, design flaws, or back doors. Sometimes called cracker to signify someone using these techniques for illegal purposes such as cracking a password or serial number. See cracker. 2. A person who acquires a sophisticated, in-depth knowledge of a system and applies this knowledge to configuring or programming the system with a high level of expertise or complexity. An elite program- mer, engineer, or technician. Two popular books on this subject are Hackers by Stephen Levy and The Cuckoo 50 Egg by Clifford Stoll. Hacker's Dictionary, The An electronic and print dictionary that evolved from The Jargon File in the early 1980s. The Hacker 50 Dictionary was an ex- panded version of The Jargon File with added com- mentary, published by Harper and Row in 1983, ed- ited by Guy Steele. The co-editors/contributors were Raphael Finkel, Don Woods, Mark Crispin, Richard M. Stallman, and Geoff Goodfellow. After nearly a decade in which it remained essentially unchanged, The Hacker 50 Dictionary was expanded beyond the artificial intelligence (AI) and hacker cultures to in- clude terms from a broad variety of computers. The 1990s version, called The New Hacker 50 Dictionary, is maintained by Eric S. Raymond and Guy L. Steele, Jr. See Jargon File, The. Hagelbarger, David W. (ca. 1921- ) An American physict and engineer, Hagelbarger taught at Aeronau- tical Engineering until 1949, where he was also re- searching the use of analog computers for engineer- ing applications. He then joined Bell Laboratories and became acolleague ofClaude Shannon. Hagelbarger implemented some of the computer gaming ideas pro- posed by Claude Shannon in 1950, developing a penny-matching machine that was pitted against 433 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary Shannon's machine (long before computer-computer chess games became popular). Hagelbarger also co- authored articles on electronics with Shannon, worked on educational computer system concepts (e.g., CARDIAC), and developed data transmission error correction codes. In the early 1980s, he was co- developing experiments with remote computing ter- minals. See Hagelbarger code. Hagelbarger code A form ofburst error correction applicable to modems carrying communications data. Hagelbarger code is a convolutional or recurrent code in which up to 6 consecutive bit errors may be cor- rected, provided there are sufficient valid bits (at least 19 bits) prior to the error segment. It is named after Bell Laboratories researcher David W. Hagelbarger, who described the application of convolutional codes to burst correction in 1959, as well as developing cir- cuitry to decode them. See Hamming code. hairpin pickup coil A device with a one-turn coil, shaped like a hairpin, used for transferring ultra high frequency (UHF) energy. hairpinning The routing of information or data through a switch in a main facility or network host and sending it out again through another switch or routing device. HAL-9000 No computer-related dictionary would be complete without mention of the intelligent computer in the science fiction movie classic 2001: A Space Odyssey. HAL stood for "Heuristically Programming Algorithmic Computer" and apparently the one-let- ter shift that spells out "IBM" was not intentional, or so say the makers of the film. If not, it's a strong enough coincidence to create an apocryphal legend. HALE See High Altitude Long Endurance. half duplex In a circuit, one-directional transmis- sions. Often half duplex circuits can transmit in ei- ther direction, but not simultaneously. Many systems which technically have bidirectional capabilities are operated in half duplex mode to reduce interference and echoes. Modems, satellite voice lines, some cel- lular radios, and speakerphones are often used in half duplex mode. half-life A property ofradioactive decay used as a quantitative measure, of interest to many different branches of science. Radioactive decay happens at widely differing rates for different materials, so half- life is not a fixed measure, but one based on our knowledge of the properties of the materials being described. The first half-life of a substance is the in- terval during which half the radioactive material is left unchanged. The second half-life is the next in- terval, during which half of the remaining radioac- tive material is unchanged, and so on. These half life measurements are used by many sci- entists including astronomers, nuclear physicists, ar- chaeologists, and geologists. half tap A bridge that is placed across conductors without disturbing the normal functioning of the con- ductors. halftap, network In data network communications, a duplicate path established between nodes or sys- tems. A half tap provides redundancy where new 434 cable is being run, as in circuits where fiber optic is replacing copper, but where it's not desirable to dis- rupt the existing network until the new cabling is functional. halftap, telephone In telephone communications, a duplicate service installed on the subscriber side of the demarcation point (usually on the customer pre- mises). This may be done in instances where there is a problem with the original circuits, or where a new system is being installed and the old one is left in place until the new one has been tested and is known to be functional. halfwave antenna An antenna designed so that its electrical length is equal to halfof the wavelength of the signal being received or transmitted. halide glass Ahalogen-based glass that is becoming of commercial interest because it may be used as a host glass doped with rare-earth elements for use in fiber-based optical amplifiers and reflective gratings. Halide glasses are transparent in the visible spectrum and, with fluoride, luminesce in a region appropriate for telecommunications transmissions. Photochromic glasses may contain silver halide crystalline forma- tions. Silver halide-coated glass or films are used as image recording media (e.g., for holographic images). ZBLAN is an important halide gas fonned through gas-film fabrication techniques that has excellent properties for ultra-low-loss optical fibers. See silica, ZBLAN. Hall, Robert N. (1919-) An American scientist who worked at General Electric from 1942 to 1946 and 1948 to 1987. He has been inducted into the National Inventors Hall of Fame for his invention ofmagne- tron technology, a subject he studied during World War II. He has received dozens of patents, including patent #2,994,018 for his development of an asym- metrically conductive magnetron. Magnetron tech- nology has been used in a wide variety of applica- tions, including radar antijamming devices and mi- crowave ovens. Hall observed interesting semiconductor electrical properties that led him to discover alloyed p-n junc- tions. In 1950, he wrote "P-N Junctions Prepared by Impurity Diffusion" in Physical Review. By 1955, he had grown silicon-based crystals for use in transis- tors. In the 1970s, he turned his interests to solar en- ergy research. Hall is also a laser pioneer. He was group leader ofa research team at the GE Research and Development Center that succeeded in creating semiconductor in- jection diode lasers, in 1962. This was to become an important light source for fiber optic communica- tions, optical storage media (e.g., CDs), and laser printers. Hall was recognized for his work with la- sers with the Marconi International Fellowship Award in 1989. See Dicke, Robert; Kao, Charles; Javan, Ali; Karbowiak, Antoni. Hall constant A description of the relationship between current-carrying conductors and magnetic fields. The Hall constant =(transverse electric field) / (magnetic field strength) x (current density). Hall effect If you take a current-carrying semi- © 2003 by CRC Press LLC conductor with a magnetic field perpendicular to the direction of the semiconductor's current, avoltage is created that lies perpendicular to both the current and the magnetic field offlux. It has practical applications in generators and modulators. Hallwachs, Wilhelm (1859-1922) A German physi- cist who developed a type ofrefractometer and who confIrmed some of the pioneerphotoelectric work of Heinrich Hertz. In 1888, Hallwach described his dis- covery of the photoemissive properties of certain sub- stances when exposed to light by using an electro- scope. He demonstrated that photoelectric cells could be used in cameras, a big boost to the evolution of television, which was just being developed at that time. Hallwachs effect In a vacuum, anegatively charged body discharges when exposed to ultraviolet light. The effect is named after Wilhelm Hallwachs. ham operator colloq. Amateur radio operator. A hob- byist radio operator engaging in noncommercial ra- dio communications. Ham operators are primarily involved in personal, public service, and training communications over approved radio frequencies. Hams have also had a long history ofvoluntarily aid- ing in search and rescue, emergency, and disaster re- lief communications to augment government or com- mercial communications or in situations where no other support is provided. The frequencies in use for amateur communications are fairly standardized throughout the globe and hams have long communi- cated across international borders. In the U.S., ham communications and the issuance of ham radio li- censes are administrated by the Federal Communi- cations Commission (FCC). Ham operators come in all ages, shapes, sizes, and colors and represent a wide spectrum ofabilities, professions, and technical ex- pertise. See American Relay Radio League. Hamming, Richard "Dick" Wesley (1915-1998) An American mathematician and software engineer, Hamming is best remembered for developing error correction codes for computing systems in the late 1940s. In 1945, he was working at Los Alamos in the computing department, executing calculations for the Manhattan Project. Hamming later codeveloped L2, based upon L1 (Bell 1) developed by V. Wolontis and D. Leagus in 1956. In the 1960s, he authored "One Man's View of Com- puter Science" in the Journal of the A eM in which he describes his views on applied mathematical ideas and practical hands-on computer programming activi- ties. Hamming accepted a teaching position at the Naval Postgraduate School after leaving Bell in 1976. He lectured at the Naval School and became Professor Emeritus until his retirement in 1997. Hamming is the author ofDigital Filters, a book on filtering ap- plications in communications and broadcast technolo- gies that is still being reprinted. The Hamming medal is awarded by the IEEE. Quite a number of Hamming quotations have been passed down through his colleagues and students, including "It is better to do the right problem the wro~p way than to do the wrong problem the right way. HammingcodeAlinear fOlWard error detection/cor- rection code system named after R. W. Hamming of Bell Laboratories. Hamming developed the system in the late 1940s and described the system in The Bell System Technical Journal in 1950 in the context of fault-resistant large-scale computing systems. He re- ferred to it as a redundant systematic code in which acertain ratio of bits was used for error detection and correction. Hamming acknowledged the tradeoffbe- tween redundancy and the accuracy and speed of the transmission. Hamming code is ablock parity mechanism that can detect single- and double-bit errors in data transmis- ~~~~~:;~~~~~~r::~f:l~:;:1:; E::~~~'~1lI one parity bit, each based upon a different combina- tion of bits. The Hamming rule for determining the number ofparity or error checking bits is related to the number oftransmitted bits. See error correction, Hagelbarger code. Hammond, Fred (1912-1999) A Canadian engineer, collector, and curator, Hammond was aco-builder of Hammond Manufacturing Company, in 1927, one of the largest historic electrical/electronic equipment manufacturers in Canada. The company started as Oliver S. Hammond's (Hammond's father) basement shop during World War I and evolved into O.S. Ham- mond & Son, including Fred Hammond and his brothers. In 1986, Hammond Manufacturing became a public company, trading on the Toronto Stock Ex- change (TSE). Hammond began building radios in the early 1920s and earned his first amateur radio license in 1929. He founded the Southern Ontario Chapter of the Quar- ter Century Wireless Association and helped build it into the largest local chapter. He was honored by the Canadian Amateur Radio Hall of Fame in 1996 and has received many other awards ofappreciation and recognition over the years. Hammond will probably be best remembered for founding the Hammond Museum ofRadio, a center that demonstrates and shares his love for radio technology for future gen- erations. Hammond held amateur radio license VE3HC, inherited from his father. See Hammond Museum of Radio. Hammond, John Hays, Jr. (1888-1965) An Ameri- can engineer and inventor who developed radio con- trol (RC) systems for vessels in the 1910s. As a schoolboy, Hammond was already experimenting with circuits and sensors. His social circle included many of the great inventors of the time, including Thomas Edison and N iko la Tesla, a fact that likely provided inspiration and encouragement for his tal- ents. While at University, he met Alexander Graham Bell and studied radiodynamics and emerging telephony technologies. Starting as apatent clerk, Hammond fa- miliarized himself with the patent process and, in a few years, amassed more than 100 patents. He stud- ied many aspects of radio technology, including 435 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary frequency modulation (PM), radio tuning, telephony, guidance systems, and much more. Many of his pat- ents were later purchased by the U.S. military for use in radio-controlled guidance systems. See frequency hopping. HammondMuseum of Radio Named after its origi- nator, Fred Hammond, the museum began as a per- sonal collection in the early days of radio and grew steadily to the point where it was moved to a new, larger facility at the Hammond Manufacturing Company's South Transfonner Plant in Guelph, On- tario, Canada, in September 1999. The collection in- cludes hundreds of historic radio receivers and trans- mitters and represents many of the important devel- opments in wireless technology. Many of the systems are still in working order or have been restored to working order. Of special interest is the Collins Col- lection, likely the largest operational exhibit of Collins Radio equipment in the world. The museum also hosts special exhibits to commemorate the dis- coveries and designs ofa variety of radio pioneers. http://www.hammondmuseumofradio.org/ HAN See home area network. See fiber to the home, home ATM network. hand off See handoff. handle A pseudonym, a nickname, often very cre- ative, humorous, or obscure. A handle indicates your personality, your interests, or helps preserve anonym- ity. Handles are frequently used on the Internet in various email messages or postings to public news forums or chat groups. handoff, handover 1. The process ofpassing on a message or transmission to the next leg in a route that takes more than one type of communications medium or more than one transmitting region. A make-before- break handover is one in which the transfer to the new leg is carried out in such a way that the user does not perceive a break in communications. 2. The process of a communication being passed through various 'hands,' usually because the user is mobile, as from one zone to another, one station to another, one trans- mitter to another, or one frequency to another. 3. In cellular communications, the transfer of the call from one cell to .the next as the subscriber moves through the various cells. Handoffs often involve frequency shifts. 4. The process ofpassing a caller to another agent, as from areceptionist to a sales representative or technical support person. handset A human interface communications trans- ceiverunit, most often associated with telephones. It's the part we pick up and hold to our ears and mouths in order to listen and speak on the phone. Handsets come in a variety of shapes, some ofwhich have names in the telephone industry. The older round handsets familiar on rotary phones are G style, whereas the newer square ones more common on mo- bile phones and phones with the buttons on the hand- set are K style handsets. handsfree A communications unit that does not re- quire the user to hold it in order to be able to com- municate with the caller. Headsets and speakerphones are examples of handsfree units in the telephone in- 436 dustry. Some phone systems pennit hands free menu selection or dialing through voice recognition. Car- mounted cell phones are becoming more prevalent, so the driver can have both hands on the wheel and concentrate on driving, rather than holding the cel- lular handset. For computer input devices, a voice recognition system can be used along with aheadset to create a handsfree unit. handsfree telephone Any telephone appliance that provides handsfree operation for some or most of its operations, such as a voice operated phone or com- puter (e.g., for spoken dialing), a speakerphone, a headset, etc. See handsfree. handshake Communication between two systems to manage synchronization of the transmitted and re- ceived signals, often established with ACK or NACK signals, tones, keywords, or header packets. Hand- shaking is an essential component of most commu- nications systems and is often incorporated into the transmission protocol itself. Handshaking can be done between people, between machines, or both. The most familiar form of handshake is the verbal "Roger" used on one-way-at-a-time radio links. It signals the other party that it's his or her turn to speak. In verbal communications, this "Roger" handshake is sometimes accompanied by electrical signals that set the half-duplex communications direction to fa- vor the person who is currently talking. There are also textual handshakes. In public chats on the Internet, where dialogs are typed rather than spo- ken, "GA" (Go Ahead) serves the same purpose as "Roger" on a radio link. In modem communications, handshakes are used to acknowledge a signal, to coordinate baud rates, and to orchestrate the transmission, receipt, and data, so the signals don't override or clobber one another. On networks, a handshake can negotiate links between computers, printers, scanners, and other peripherals that might not always be online or might be shared (or transmit at different data rates from the main net- work). See auto-negotiation. handwriting recognition A software application, often coupled with ascanning device or a stylus that resembles a pen, that recognizes and may also inter- pret written script. It may further translate the digi- tized handwritten text into displayable typewriter- style text, depending upon the application. Pen com- puting uses this type oftechnology and is of use to those who don't know how to type or don't want to. Since handwriting is widely variable, most systems must be trained to recognize an individual's writing and, even then, the results may not be perfect. Nevertheless, in the shipping industry, scientific field work, and other areas, handwriting recognition is use- ful as afonn of user interface, and the technology will eventually improve to the point where anyone's hand- writing can be recognized and interpreted by a com- puter. Fiber optic faceplates, that may be used in place oftraditional optical scanning lenses, may add new dimensions to handwriting recognition as a security or input mechanism and may increase the active re- gion over which the writing may be scanned. © 2003 by CRC Press LLC Some handwriting recognition applications are con- troversial. The use of electronic signature pads for the acceptance of courier packages means that a company has your signature, in electronic fonn, in a database. It is not possible for an employer to monitor the ac- tivities of every employee at every moment and thus it is extremely important to secure, limit access to, and purge this database. But, since there has been no verbal or written agreement between the user and the courier as to how the handwritten signature may be used, there is little legal protection for the person who has innocently given their signature to receive their package. This opens the door to many types of per- sonal intrusion and illegal activity, including identity theft, fraud, and blackmail. See Personal Digital As- sistant. hang up lJ. To disconnect from a transmission (two words when it is a verb). On modems, ATH is the Hayes-compatible command for hanging up. On phones, a hangup (one word when it is a noun) oc- curs when the button is pressed for at least a specific amount of time. In some areas, the callee may not be able to hang up this way if the caller is still on the line. It doesn't work the other way though; if the caller hangs up and the callee is still on the line, the trans- mission is disconnected. Many Internet Service Pro- viders (ISPs) will automatically hang up (terminate) a computer connection if there is no activity after a certain amount of time, such as 10 minutes. Hansell, ClarenceWeston (1898-1967) An Ameri- can research engineer and television pioneer in New York state, Hansell worked for a year for General Electric, then the Radio Corporation of America (RCA), and later for the U.S. government as a scien- tific investigator with the Technical Industrial Intel- ligence Committee in Germany, during World War I!. In the 1920s, Hansell worked with Scottish inventor John L. Baird on the development ofa mechanical television system based upon the idea ofusing an ar- ray oftransparent rods (essentially a fiber optic sys- tern) to transmit broadcast and facsimile images. In 1925, Hansell founded the RCA Radio Transmis- sion Laboratory at Rocky Point, N.Y. at which the world's largest radio transmitting station was devel- oped. Due to the relationship between radio transmis- sions and the Earth's atmosphere, he also became in- terested in ionization effects and climatology. Hansell was a member of many prominent science institutes and engineering societies. A collection of his papers from 1928 to 1967 are housed in the State University of New York (Stony Brook). See Baird, John. Hansen, Holger MollerADanish scientist who in- vestigated the transmission of images through bundles ofparallel glass fibers in the late 1940s and early 1950s. Hansen applied for a patent for cladded glass or fiber imaging in 1951, but was denied the patent due to the prior work of Hansell and Baird on television technologies in the 1 920s. Without a patent, it was difficult to get funding for commercialization of the invention. Hansen, William Webster (1909-1949) An Ameri- can physicist and educator with apioneering interest in the use of high-frequency radio waves (micro- waves) in particle acceleration research. Hansen joined the staff at Stanford University in 1934. He was an associate ofMartin Packard, working on a team with renowned physicist Felix Bloch. In the 1930s, Hansen began his association with Russell and Sigurd Varian, working in the basement of the Stanford physics building. When the inventive Russell Varian sketched out an idea for a Rumbatron Oscillator or Amplifier, in July 1937, it was Hansen who had provided the basic rumbatron concept and the calculations to support the viability of Varian's idea, leading to the invention of the Klystron tube. Hansen subsequently did important work in micro- wave theory and passed on the knowledge through courses at Stanford while the Varians developed prac- tical applications of the Klystron technology for ra- dar and communications. Following World War II, Hansen returned to his research interests and pioneer work in disk-loaded accelerators. He demonstrated alinear accelerator in 1947, sponsored by the Office of Naval Research. It led to the later creation of the Stanford Linear Accelerator Center (SLAC) and many discoveries in basic particle physics and X-ray spectroscopy. The basement lab had evolved into the Microwave Laboratory, which eventually became the Ginzton Laboratory and the Hansen Experimental Physics Laboratory. See Ginzton, Edward; Klystron; Mark accelerators. hard copy An image or document that is readable by looking directly at the medium on which it is tran- scribed, as on a piece of paper, cardboard, stone, or parchment. Asoft copy must be accessed with some type oftechnology in order to be viewed, manipu- lated, or displayed. Soft copies commonly exist on hard drives, floppy diskettes, tapes, CDs, and other magnetic or optical media. hard disk drive, fIXed disk drive HDD. A data stor- age device most often associated with desktop com- puting systems although it is also useful for storage in computerized milling machines and other indus- trial automation products. In the early days of com- puting, program code and data were stored on paper tapes, punch cards, and magnetic tape spools and cas- settes. All ofthese early devices, as they were imple- mented at the time, were essentially linear/serial de- vices with limitations in speed and flexibility. In the 1950s, ffiM engineers claimed leadership in data storage with the invention ofa high-speed ran- dom-access device. The release of the 305 Random Access Method of Accounting and Control (RAMAC), in 1956, made it possible to store five megabytes on 50 24-inch discs. The machine weighed more than a ton. In the early 1970s, sealed disks known as Winchester disks were introduced and the name became generic for disk drives for several years. Floppy disk drives were an inexpensive alternative to the new, expensive hard disk drives sold during the 1970s and the 1980s, but by the late 1980s, hard disk drives became the dominant storage medium and 437 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary floppy drives were used mainly for program distri- bution and swapping small files among computer systems. In 1986, the American Society of Me chan i- cal Engineers declared ffiM's contribution as an In- ternational Historic Mechanical Engineering Land- mark. The following year redundant arrays of inde- pendent disks (RAID) technology was patented. The hard drive as we know it is based upon a rotat- ing circular platter with a read/write head that never travels very far from any specific location on the plat- ter, thus providing not only random access, but also high-speed access, compared to previous methods. One or more magnetic platters are permanently con- tained within a fixed housing (as opposed to car- tridges or other portable storage devices), hence the name hard or fixed disk. When a drive is formatted, the magnetic particles are aligned to a specific pat- tern and, from that point, data is written by influenc- ing the particles and read by detecting the state of the particles on the magnetic surface. Compared to floppy diskettes, the hard drive can hold far more informa- tion and is safe from dust and fingerprints. IBM's claim that hard drives would revolutionize computer storage was correct, as hard drives quickly superseded tape drives for most realtime applications. (Tape was retained for backup purposes due to its lower cost and was later reintroduced as a random-access removable medium, popular in the 1990s.) Hard drives were originally expensive washing ma- chine-sized devices purchased by institutions for mainframe computers, but by the early 1980s, hard drives were smaller and more accessible and avail- able for the desktop market as well. A five megabyte hard drive in abreadbox-sized housing could be pur- chased for under $1,000 and soon smaller, higher- storage drives were available for a few hundred dol- lars. Another consequence of smaller drives was port- ability. By the early 1990s it was possible to equip portable computers with high-capacity drives and removable hard drives were built into some models. Hard drives have been developed in a number of for- mats, too numerous to list here. However, the most common hard drive controller/hard drive formats on desktop systems during the 1980s and 1990s were 1. Small Computer System Interface (SCSI) - a ro- bust format that could be daisy-chained (usually up to seven devices) to include several drives or could be used in RAID systems. SCSI was in- stalled in most Motorola-based machines includ- ing Macintosh, Amiga, and many workstation computers. 2. Integrated Drive Electronics (IDE) - a more lim- ited master/slave format introduced to bring the price down on drives for popular Intel-based ma- chines serving price-conscious consumer mar- kets. These drives became prevalent on ffiM/ IBM-licensed computers sold to homes and small businesses in the 1990s. Due to limitations in capacity and expandability, a new enhanced IDE format was introduced as EIDE. EIDE was essentially a move to give IDE the capabilities familiar to SCSI users. 438 Improvements in hard drive capacity have been strongly tied to the ability of the read/write head to read and write data of finer precision and higher den- sities. Thin films were introduced in the late I 970s, along with the run-length-limited (RLL) data-encod- ing scheme. In the early 1990s, ffiM introduced mag- netoresistive head technologies based on discoveries in the late 1980s of high magnetic field effects on crystals. With more sensitive sensors came higher- capacity hard drives, with significant breakthroughs resulting from the development ofgiant magnetore- sistive (GMR) head technologies. SCSI and IDE had a relatively long reign, consider- ing the pace ofcomputer technology, but Universal Serial Bus (USB) and FireWire drives were making inroads by 2001. The USB data transmission standard was developed by a consortium of companies (Compaq, DEC, ffiM, Intel, Microsoft, NEC, North- ern Telecom) in the mid-1990s. USB hard drives have several advantages over previous formats, including small size, hot-swapping capability, portability, and high capacity, all at areasonable price. Fire Wire was developed by Apple Computer and the IEEE 1394 Working Group. Its principal advantages are speed and ease of use, which make it suitable for hard drive and other demanding transmission technologies (e.g., video). Given their many benefits, USB and FireWire may quickly supersede both IDE and SCSI formats on consumer machines, although updated SCSI for- mats, including Ultra SCSI and Wide Ultra SCSI may continue to serve workstation and service provider environments where very high transmission speeds are desired. See disk controller, redundant array of inexpensive disks, superparamagnetic. hard sectored Astorage medium, usually magnetic, in which the various boundaries or sectors are physi- cally designated with holes, pits, ridges, or other markers to indicate their extents. Hard sectored me- dia are becoming less common than soft sectored as they are less transportable between different systems. hard transfer A term for an electronic monetary transaction involving the actual exchange of funds be- tween individuals or banking institutions. A hard transfer often follows a soft transfer. Apaper check is a type of soft transfer. It is a monetary transaction that is not actually finalized until the money is with- drawn from the bank. Similarly, online there are many monetary transactions that are soft transferred and later hard transferred from the actual bank or other financial institution. hard tube A type of electron tube that has a high vacuum environment within the sealed glass bulb. hard wired See hardwired. hardware The physical circuits and devices associ- ated with systems, especially computerized systems, that are fixed or hard wired and unlikely to be altered by the user. Contrast with software (although the dis- tinction is not actually cut and dry), which is selected and swapped out by the user, modified, or over- written. See firmware, software. hardware flow control Acapability built into most of the high speed serial card modem combinations © 2003 by CRC Press LLC that helps to handle data flow control. Use of hard- ware flow control may also require the use ofa hard- ware flow control cable. hardware interrupt On computing systems, a call to the software to interrupt the current process in or- der that it may temporarily listen to or interact with a hardware device interfaced with the system. See in- terrupt, IRQ. hardwired I. A circuit that is intended as permanent or is not expected to change in the near future, and thus it is wired in such a way as to make it efficient to produce or easy to use, rather than making it ame- nable to change. Contrast this arrangement to patch bays and breadboards, which are intended to proto- type temporary circuits and are easy to change. Pro- grams or pathways built into computer motherboards are typically hardwired, whereas the various user- added peripherals, especially those that fit into slots or chips designed to be swapped out when better tech- nology is developed, are considered to be modular or configurable and not hardwired. 2. People who are hardwired are said to be set in their ways, not ame- nable to change or open to new ideas. 3. An idea or system that is hardwired is one that is entrenched, dif- ficult to change for various reasons, including poli- tics, economics, or complexity. Harmon, Leon D. (1922- )A Bell Telephone Labo- ratories researcher who initiated a project to simu- late the functions ofbiological nerve cells by means of simple transistors. These could be closely associ- ated with one another in arrays and were applied in a simulation of mammalian eye nerves. His work was featured in industry journals in the late 1950s and in the film Thinking Machines in 1960. Harmon chaired workshops sponsored by the National Science Foun- dation (NSF) in the mid-1970s. Harmon was a pioneer cyberneticist interested in machine simulation of aspects of human perception. Long before most others, Harmon could see the prac- tical applications of recognition technologies. In this vein, he coauthored a number of articles on charac- ter recognition, human face recognition, and automa- tion of these processes by intelligent systems in the early 1970s. He also collaborated in a number of projects with Ken Knowlton, and together they did experiments in scanning images and reconstituting them with computer algorithms, thus creating some of the first examples of computer graphics and im- age processing as they relate to human perception. See Knowlton, Kenneth; neural network; Shroeder, ManfredR. harness A securing system of straps, combination connectors, or other means used to consolidate mul- tiple cables so they can be handled more easily as a unit. Harris Broadcast Communications, Harris Cor- poration An international, publicly traded commer- cial provider of advanced broadcast technologies, Harris is one of the pioneer developers and provid- ers of digital broadcast technologies. It contributed the radio frequency Test Bed for the Advanced Tele- vision Test Center in 1990, was first to market with a number of digital television exciter and transmissions products, the first to transmit a commercial HDTV signal, and the first to establish an operating digital television air-chain. Harris also broadcast the first major live high-definition television (HDTV) sports event in 1997. In 1999, Harris and the CPBIWGBH National Center for Accessible Media demonstrated digital closed caption and descriptive narration tech- nologies at the National Association of Broadcasters conference. In April 2001, Harris announced a business arrange- ment with Dotcast, Inc., to provide digital content through a revolutionary network that takes advantage of advances in broadcast technology. It provides popular computer services available on the Internet, ~~:~: ::~~f~r:7~:~S~:~w!~~~~~~~:: ~e~:~ II Harris Corporation is also a provider of computer security products, distributing network analyzing and scanning software to clients such as the Canadian Pub- lic Works and Government Services. Harris has con- tributed to the development of the European Digital Video Broadcast (DVB) standard. See Advanced Television Test Center; Association for Maximum Service Television, Inc.; KLAS- TV. Harrison, John (1693-1776) ABritish clockmaker who devised a means, in the 1770s, to create a por- table chronometer to aid in marine navigation by de- termining longitude, even when being bumped around by heavy seas. Several countries have ac- knowledged Harrison's contribution with commemo- rative postage stamps. Harvard Mark I A historically significant, large- scale, automatic computer constructed by Howard H. Aiken and ffiM engineers in the early 1940s. The concept was proposed by Aiken as he was finishing his graduate work at Harvard University in 1939. In his report, Aiken envisioned a calculating machine that embodied some of the concepts of Charles Babbage, one that could handle cumbersome math- ematical equations too lengthy or time-consuming for humans. Aiken's concept led to support from Inter- national Business Machines (ffiM) to build the ma- chine at the ffiM labs in Endicott. Although most of- ten remembered as the Mark L it was also known at the time as the IBM Automatic Sequence Control Cal- culator. The Mark I was a 35-ton electromechanical behemoth that had a number ofcharacteristics to distinguish it from basic calculating machines, making it a true his- toric computer. It used magnetically operated switches to handle the logic patterns, included cen- tral processing units and multiple storage registers, and could run (and rerun) instructions stored on prepunched paper tape. For the realization ofAiken's goals, it was capable of working out mathematical equations to 23 significant digits. By the spring of 1944, the machine had been moved from the ffiM labs to Harvard University and began to be known as the Mark I. At Harvard it was put into service by the U.S. Navy for military calculations in 439 © 2003 by CRC Press LLC Fiber Optics Illustrated Dictionary the aftermath of World War II. Three programmers were involved on the project in the 1940s; the best remembered is Grace Hopper, who joined the project in 1944, after Richard Bloch and Robert Campbell. See Aiken, Howard; Hollerith, Herman; Hopper, Grace. Harvard Mark n The second in the series of large- scale computing machines developed under the di- rection of Howard Aiken, the Mark II was designed to replace some of the mechanical elements of the Mark I with electronics. It also took advantage of some of the improvements in electronics technolo- gies that had occurred since the early 1940s. World War II and the need for fast, complex computations provided motivation for funding and building more advanced computers after the success of the Mark I computer. The Mark II was completed in 1947 and Aiken put his attention to the development of the Mark III. Harvard Mark m Third in the line of large-scale computing machines developed under the direction of Howard Aiken, the Mark ill was delivered in 1951 to the u.S. Naval Surface Weapons Center. It im- proved upon earlier Mark computers and on many competitors by incorporating drum memory with separate drums for instructions and data. Harvard Mark IV Fourth in the line oflarge-scale computing machines developed under the direction of Howard Aiken, the Mark IV was the last in the se- ries, with Aiken working on the project until 1952. Hau,LeneVestergaard (ca. 1959-)A Danish physi- cist who graduated from the University of Arhus, Hau joined the Department of Physics at Harvard Univer- sity where she has achieved the remarkable accom- plishment of stopping light - without losing its en- ergy. In 1998, Hau's research group succeeded in slowing light to a speed of only 17 mls by optically inducing quantum interference in aBose-Einstein condensate. By January 2001, it was announced that this line of inquiry had led to the spectacular feat of stopping light emitted from a laser and releasing it again at full speed and intensity, in a sense creating a low-loss (or no-loss) atomic optical "capacitor." Fiber optics has been one of the breakthrough tech- nologies in communications media, but Hau's group has gone beyond this concept, creating a dynamic system of atoms and photons with optical properties with a nonlinear refractive index orders of magnitude greater than an optical fiber or any other transmis- sion medium. These developments will have far- reaching consequences for new scientific research and applied technologies. It may be possible to cre- ate single-photon optical switches, entirely new classes of computer components, and light-based stor- age devices unlike any oftheir predecessors. Hauksbee the Elder, Francis (ca. 1666-1713) An English artisan and experimenter who built on the work ofR. Boyle and associated with Isaac Newton. Hauksbee did studies in static electricity and created a pump, in the early 1700s, that apparently improved upon earlier designs and prevailed for the next century 440 and a half. The availability of pump technology was important not only for commercial pumping of oil and water, but because the ability to create a good vacuum was invaluable to scientific exploration and the study of sound transmission, magnetism, and electricity. A Hauksbee air pump, ca. 1708, is listed in the King George III Collection at the London Science Mu- seum, and there is a ca. 1720 Hauksbee pump in the Museum of the History of Science in Oxford. When he was joined by James Hodgson, in 1702, Hauksbee was already employed by the Royal Soci- ety to demonstrate experiments. By 1705, he was an instrument supplier and became a fellow of the Royal Society, the same year he reported on his experiments with producing light in a mostly evacuated mercury vessel. At about the time he started giving science lectures with James Hodgson. Hauksbee's research led to further experiments, and the observation that lampblack particles would move up and down very rapidly and make an audible sound when a glass tube that had been rubbed was held above the particles. Following this observation, he devised a rotating wheel to allow the glass to be rubbed at a great rate, in essence inventing a friction generator. In 1709, Hauksbee described his discoveries in his self-published Physico-Mechanical Experiments on Various Subjects. The book was republished in Ital- ian in 1716 and in English in 1719 by J. Senex in a larger edition with several new experiments. In 1754, a French edition was released. Hauksbee also de- scribed experiments with capillary action in Philo- sophical Transactions, in 17 12. Hauksbee did not have an extensive formal educa- tion and was not highly literate, but his mechanical aptitude and talent for experimentation were excep- tional and earned him the respect of his peers. See barometer; Boyle, Robert; Gray, Stephen; Guericke, Otto von; Hodgson, James. [Source for birth/death dates: Jeanette (Jan) Shermer, descendant.] HauksbeetheYounger, Francis (ca. 1687-1763) An English instrument maker and scientist, the nephew ofFrancis Hauksbee, the Elder, listed here mainly to distinguish him from his uncle of the same naple with whom he is often confused (Hauksbee the Younger was also a member of the Royal Society). Hauksbee carried on the tradition ofexperimentation and sci- entific inquiry of his uncle and set up an outlet for the distribution of scientific devices. The Charles Townshend Papers list a 1757 communication about a Francis Hauksbee having developed medicine for the treatment of venereal disease. Hayes Microcomputer Products Inc. One of the early entrants to the modem market, Hayes set many of the industry'S de facto standards for serial com- munications through modems. Hayes modem control commands are still widely used. See AT commands. Hayes Standard AT commands See AT commands. HBA See host bus adapter. HBS See Home Base Station. Hell. See Host Command Interface. 2. human com- puter interface. 3. See Human Computer Interface standards. © 2003 by CRC Press LLC HCP hard clad plastic. A material used in fiber optic cable construction. HCS hard clad silica. A material used in fiber optic cable construction. HD See half duplex. HDB3 High-Density Bipolar Three. A signaling scheme used in high-speed digital networks, espe- cially phone networks. HOB3 is based upon Alter- nate Mark Inversion (AMI) and uses positive and negative pulse states. If four or more zeroes are se- quentially transmitted, HOB3 inserts a violation code, an enhancement on basic AMI transmission. The in- sertion of the violation bits facilitates the reconstruc- tion of the signal at the receiving end. HOB3 and other enhanced signaling schemes have been super- seding AMI. See Alternate Mark Inversion, B8ZS. HDCM See high-resolution direct core monitoring. HDD See hard disk drive. HDLC See High Level Data Link Control. HDSL See high bit-rate Digital Subscriber Line. HDT Host Digital Terminal. HDTV See High Definition Television. headA device for reading, writing, or removing data from a volatile storage medium (usually magnetic). VCRs, hard drives, floppy drives, and tape recorders all have heads that touch, or nearly touch, the surface of the storage medium in order to transmit the infor- mation to the logic circuits or mechanisms that de- code the information into human-meaningful form or to write to the storage medium. head thrashing If read and/or write heads on stor- age mechanisms encounter hardware or software problems, especially bad sectors, the mechanism may start to oscillate rapidly, sometimes uncontrollably. This can lead to damage to the head or the data if not terminated in time. header 1. Identifying text printed in a block at the head ofa file or document. Header information fre- quently includes file format, version, date of creation, author, and typographic information. Header files are common to word processing, desktop publishing, and EDI applications. 2. A commonly used system rou- tine contained in a separate file and referenced dur- ing program compilation and linking. System windowing routines and graphics routines are fre- quently linked in from header files. A header provides modularity and a write-once-use-many solution to many programming tasks. 3. In ATM, the protocol control information located at the beginning ofa pro- toco I data unit. headerarea In an EDI file, the area that contains the header information for the document. See EDI, header. Header Error Control HEC. In ATM transmissions, an error detection mechanism contained in a byte at the end of the 53-byteATM header. It corrects single bit errors and is efficient over transmissions media with low bit error rates (BERs) such as fiber optic cable. In ATM carried over wireless transmissions, the signal is not as clean as a fiber optic signal, and the BER rate can be substantially higher. Satellite transmissions tend to be especially bursty, a situation not handled well with a single bit error mechanism. Some satellite service providers have compensated for this by developing a variety of solutions, includ- ing interleaving of cells to isolate the data from burst errors. See ATM Link Enhancer. headset A radio or telephone transceiver unit worn on the head or wrapped around the ear (sometimes referred to more specifically as an earset). Headsets are typically used by professionals who sit and take many calls, including receptionists, console atten- dants, telemarketers, and reservation takers and by those on the move, including truckers, warehousers, and ground staff. Headsets are also becoming a con- sumer item for use with cellular phones (so drivers can keep both hands on the wheel) and other hands- free applications. heap memory A type of local memory storage that is dynamically allocated while a program is running. Heap memory is usually of more concern to applica- tions programmers than to users, but there are some applications in which heap memory nee~ to be set prior to running the software in order to provide enough working room for memory-intensive appli- cations. On some systems, heap memory is limited to a maximum of 64 kilobytes. heatsinkA structure for dissipating or radiating heat away from a heat -generating device such as a motor or semiconductor. Heat sinks often resemble open coils, flat fence rails, or other repeated, spaced ele- ments, usually of metal, that are configured to in- crease their surface area, and thus their radiating ca- pacity. Sometimes the component is called a cooling fin. Some CPU s require surprisingly large heat sinks, es- pecially accelerator chips intended to provide faster performance. See dissipate, baffle. Heathkit EC-l Educational Analog Computer A historic hobbyist computer, introduced in 1959 or 1960 as a Heathkit, a Daystrom product line that was very popular with computer hobbyists in the late 1970s and early 1980s (until it became cheaper to buy a system than to build one from a kit). The EC-l (Edu- cational Computer-I) was one of the earliest low-cost desktop computers, selling for $199, and one of the last of the analog computers. It had a steel chassis supporting rows of knobs and status lights, looking much like the Altair digital computer that came out a decade and ahalf later, and it could do basic calcula- tions. It was marketed mainly to educational institu- tions teaching applied physics and mathematics. See Altair, Arkay CT-650, GENIAC, Kenbak-l, Simon. Heaviside layer See Kennelly-Heaviside layer. Heaviside, Oliver (1850-1925) An English physi- cist who started as a telegrapher. He later became in- terested in electricity and began publishing on that subject in 1872. He made thorough studies of Maxwell's equations and then set about simplifying them to two equations expressed in two variables. Along with J. J. Thompson, Heaviside theorized about the electromagnetic reactions and mass of elec- trically charged particles in motion. See Kennelly- Heaviside layer, Maxwell's equations. 441 © 2003 by CRC Press LLC . number of frequen- cies, including S-band and L-band (radar) commu- nications. H channel An lTU-T-defined transmission channel on packet-switched networks consisting of aggre- gated B channels. Fiber Optics Illustrated Dictionary lTU-T G Series Recommendations, cont. General andmisceUaneous,cont. G.411 1988 0.431 1988 0 .451 1988 0.702 1988 0.703 1991 G.704. repre- sent horizontal and vertical sync pulse components. See negative-going video. H-plane bend See H bend. HO Channel In ATM networking, a 384-Kbps chan- nel consisting of six contiguous OS-Os (64 Kbps) of aT1transmission line. back v. 1. To quickly cobble together