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..
Trang 1Fiber Optics Illustrated Dictionary
lTU-TGSeries 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 ofthe
informationviewpointforthe management of a transport network
0.853.21996 Subnetwork connection
managementinformation viewpoint
G.854.11996 Managementof thetransport
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
functionalaccess networks(AN)
architecture and functions, access types,management,and service node aspects
Digital sections based on the
2048kbps hierarchy Digitalline sectionsat 3152kbps Digital line systems providedby FDMtransmission bearers General considerations on digital line systems
Digitallinesystems basedon the
1544kbps hierarchy on
symmetricpaircables 0.952 1988 Digital line· systemsbasedon the
2048bps hierarchy on symmetric pair cables
0.953 1988 Digital line systems based onthe
1544.1.<bpshierarchyOIlco·axial pair cables
0.954« 1988 DigitallinesystelP-Sbased on the
2048kbps hierarchy on coaxial pair cables
Digitalline systems based onthe
1544kbps andthe2048kbps
hierarchy onopticalfibre cables
Access digital section for ISDN basic rate access
Access digitalsectionfor ISDN primary rate at2048kbps Access digital section for ISDN primaryrateat1544 kbps V-Interfaces at the digital10cal exchange(LE) •• •
v~Interfacesat thedigital 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 Protectionof pilots and
additional·measuring
frequenciesat points wherethere
is a through-connection
Useofradio-relay systems for
international telephone circuits
Hypothetical· reference circuits
forfrequency-divisionmultiplex
(FIlM) radio-relaysystems
Use of radio linksin
futemationaltelephone circuits
Digitalhierarchybit rates
.PhysicaVelectrical
characteristics ofhierarchical
digital interfaces
Synchronous frame structures
used at1544, 6312, 2048, 8488,
and44,736kbpshierarchical
levels
G.706 1991 Framealignment and cyclic
redundancycheck (CGC)
proceduresrelatingto basic
frame structures definedin
Recommendation··G.704
Network node interface for the
synchronous digital hierarchy
7-kF(z audio-coding within 64
kbps
General characteristics of a
60-channeltranscoderequipment
Oeneral characteristicsof a
48-channel transcoder equipment
Pac~tcircuit multiplication
equipment
FacsimiledemodulationJ
remodulationfor digital circuit
multiplication·cquipment
Protected monitoring points
provided on digital transmission
systems
Characteristics of cadecs for FDM
assemblies
Characteristics of a 64-kbps
cross-connectequipment with2048
kbpsaccess ports
0.804 1993 ATM.cc:lltn8pping jot()
plesiochronous digital hierarchy
(FllID
0.805 ·1995 Genericftmctional architecture of
transportnetwt}rks
Trang 2tal 3.symb.horizontal linear polarization(lTV).
H bend, H-plane bendA smooth transition in the
orientation of the axis of an electromagnetic
waveguide such that the axis remains parallel to the
direction ofthe magnetic H-field polarization
(trans-verse polarization) The H fields become distorted in
a waveguide with an H bend The degree ofbend
de-pends upon the frequency ofthe 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 channelAnlTU-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 driveInanalog 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 acomposite
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 bendSee H bend
HO ChannelIn ATM networking, a 384-Kbps
chan-nel consisting of six contiguous OS-Os (64 Kbps) of
a T1 transmission line
backv. 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
area/process for which the person does not have au-thorization
hack intoTo find a means ofentrance other than the normal way, to compromise the security ofa system
by exploiting a weakness 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 calledcrackerto 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 areHackersby Stephen Levy and The Cuckoo 50 Eggby Clifford Stoll
Hacker's Dictionary, TheAn electronic and print dictionary that evolved from The Jargon File in the early 1980s The Hacker 50 Dictionarywas 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 Dictionarywas expanded beyond the artificial intelligence (AI) and hacker cultures to in-clude terms from a broad variety of computers The 1990s version, calledThe New Hacker 50 Dictionary,
is maintained by Eric S Raymond and GuyL.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 a colleague ofClaude Shannon Hagelbarger implemented some ofthe computer gaming ideas pro-posed by Claude Shannon in 1950, developing a penny-matching machine that was pitted against
Trang 3Fiber 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 codeA form of burst error correction
applicable to modems carrying communications data
Hagelbarger code is aconvolutionalorrecurrentcode
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 ofconvolutional codes
to burst correction in 1959, as well as developing
cir-cuitry to decode them See Hamming code
hairpin pickup coilA device with a one-turn coil,
shaped like a hairpin, used for transferring ultra high
frequency (UHF) energy
hairpinningThe 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 ofthe intelligent computer
in the science fiction movie classic2001: A Space
Odyssey.HALstood 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 duplexIn 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-lifeA property of radioactive 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 theremaining
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 tapA bridge that is placed across conductors
without disturbing the normal functioning ofthe
con-ductors
half tap, networkIn data network communications,
a duplicate path established between nodes or
sys-tems A half tap provides redundancy where new
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
half tap, telephoneIn 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
half wave antennaAnantenna designed so that its electrical length is equal to half of the wavelength of the signal being received or transmitted
halide glassA halogen-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 ofpatents, 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" inPhysical Review.By1955, 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 of a 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 constantA description of the relationship between current-carrying conductors and magnetic fields The Hall constant=(transverse electric field) / (magnetic field strength) x (current density) Hall effectIf you take a current-carrying
Trang 4semi-direction ofthe semiconductor's current, a voltage 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) AGerman
physi-cist who developed a type of refractometer and who
confIrmed some ofthe pioneer photoelectric work of
Heinrich Hertz In 1888, Hallwach described his
dis-covery ofthe photoemissive properties ofcertain
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 effectIn a vacuum, a negatively charged
body discharges when exposed to ultraviolet light
The effect is named after Wilhelm Hallwachs
ham operatorcolloq.Amateur radio operator
Ahob-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-liefcommunications 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 of abilities, professions, and technical
ex-pertise See American Relay Radio League
Hamming, Richard "Dick" Wesley(1915-1998)
AnAmerican mathematician and software engineer,
Hamming is best remembered for developing error
correction codes for computing systems in the late
1940s.In1945, 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
ofCom-puter Science" in theJournal of the A eMin 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"Itis better to do the right problem the
way
Hamming codeA linear 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 inThe Bell System Technical Journalin 1950 in the context of fault-resistant large-scale computing systems He re-ferred to it as aredundant systematiccode in which
a certain ratio ofbits was used for error detection and correction Hamming acknowledged the tradeoffbe-tween redundancy and the accuracy and speed ofthe transmission
Hamming code is a block 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 of parity or error checking bits is related to the number of transmitted bits See error correction, Hagelbarger code
Hammond, Fred(1912-1999) ACanadian engineer, collector, and curator, Hammond was a co-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 HamHam-mond 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 of appreciation and recognition over the years Hammond will probably
be best remembered for founding the Hammond Museum of Radio, 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 Nikola 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 a patent 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
Trang 5Fiber Optics Illustrated Dictionary
frequency modulation (PM), radio tuning, telephony,
guidance systems, and much more Many ofhis
pat-ents were later purchased by the U.S military for use
in radio-controlled guidance systems See frequency
hopping
Hammond Museum ofRadioNamed 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 ofhistoric radio receivers and
trans-mitters and represents many of the important
devel-opments in wireless technology Many ofthe systems
are still in working order or have been restored to
working order Of special interest is theCollins
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 of a variety of radio pioneers
http://www.hammondmuseumofradio.org/
HAN See home area network See fiber to the home,
home ATM network
hand offSee handoff
handleA pseudonym, a nickname, often very
cre-ative, humorous, or obscure Ahandle 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, handover1 The process of passing on a
message or transmission to the next leg in a route that
takes more than one type ofcommunications medium
or more than one transmitting region A
make-before-breakhandover 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 ofthe call from
one cell to the next as the subscriber moves through
the various cells Handoffs often involve frequency
shifts 4 The process of passing a caller to another
agent, as from a receptionist to a sales representative
or technical support person
handsetA 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 of which 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 handhand-sets
handsfreeA 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-dustry Some phone systems pennit handsfree menu selection or dialing through voice recognition Car-mounted cell phones are becoming more prevalent,
so the driver can have both hands on thewheel and
concentrate on driving, rather than holding the cel-lular handset For computer input devices, a voice recognition system can be used along with a headset
to create a handsfree unit
handsfree telephoneAny 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
handshakeCommunication 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 herturnto speak
Inverbal 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 recognitionA software application, often coupled with a scanning 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 of technology 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 a fonn ofuser 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 usedinplace
of traditional 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
Trang 6troversial The use ofelectronic signature pads for the
acceptance ofcourier 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 ofevery 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 uplJ.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 oftime.Insome 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; ifthe 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, Clarence Weston(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!
Inthe 1920s, Hansell worked with Scottish inventor
John L Baird on the development of a mechanical
television system based upon the idea ofusing an
ar-ray of transparent rods (essentially a fiber optic
sys-tern) to transmit broadcast and facsimile images
In1925, 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 MollerA Danish scientist who
in-vestigated the transmission of images through
bundles of parallel 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 1920s Without a patent,
it was difficult to get funding for commercialization
of the invention
can physicist and educator with a pioneering 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 of Martin 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 ofthe 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
a linear 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 copyAn 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 A soft copy must be accessed with some type of technology 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 driveHDD 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 of a 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
Trang 7Fiber Optics Illustrated Dictionary
floppy drives were used mainly for program
distri-bution and swapping small files among computer
systems In 1986, the American Society
ofMechani-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 detectinfluenc-ing the state ofthe
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 a breadbox-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 ofsmaller 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
offor-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
Improvements in hard drive capacity have been strongly tied to the ability of the read/write head to read and write data offiner precision and higher den-sities Thin films were introduced in the late I970s, 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 of giant magnetore-sistive (GMR) head technologies
SCSI and IDE had a relatively long reign, consider-ing the pace of computer 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 a reasonable price FireWire was developed by Apple Computer and the IEEE 1394 Working Group Its principal advantages are speed and ease ofuse, 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 A storage 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 offunds be-tween individuals or banking institutions A hard transfer often follows a soft transfer A paper 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 A capability built into most
of the high speed serial card modem combinations
Trang 8ware flow control may also require the use of a
hard-ware flow control cable
hardware interruptOn 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.Acircuit 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
hardwiredare said to be set in their ways, not
ame-nable to change or open to new ideas 3.Anidea or
system that is hardwired is one that is entrenched,
dif-ficult to change for various reasons, including
poli-tics, economics, or complexity
Harmon, LeonD (1922- ) ABell Telephone
Labo-ratories researcher who initiated a project to
simu-late the functions of biological 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 ofrecognition 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
harnessA 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-porationAninternational, 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
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 ofBroadcasters 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) A British 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 MarkI 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 MarkLit was also known at
the time as the IBMAutomatic Sequence Control
Cal-culator.
The Mark I was a 35-ton electromechanical behemoth that had a number of characteristics 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 MarkI.At Harvard it was put into service by the U.S Navy for military calculations in
Trang 9Fiber 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 MarknThe 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
WarIIand 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 MarkmThird in the line of large-scale
computing machines developed under the direction
ofHoward Aiken, the Markillwas 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 IVFourth in the line of large-scale
computing machines developed under the direction
ofHoward Aiken, the MarkIVwas the last in the
se-ries, with Aiken working on the project until 1952
Hau, Lene Vestergaard(ca 1959- )ADanish
physi-cist who graduated from the University ofArhus, Hau
joined the Department ofPhysics at Harvard
Univer-sity where she has achieved the remarkable
accom-plishment of stopping light - without losing its
en-ergy
In1998, Hau's research group succeeded in slowing
light to a speed of only 17mlsby optically inducing
quantum interference in a Bose-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 ofmagnitude
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 ofcomputer components, and light-based
stor-age devices unlike any of their 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
and a half The availability ofpump technology was important not only forcommercialpumping ofoil and water, but because the ability to create a good vacuum
was invaluable to scientific exploration and the study
ofsound 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 ofthe 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-publishedPhysico-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.In1754,
a French edition was released Hauksbee also de-scribed experiments with capillary action in Philo-sophical Transactions,in 1712
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.]
Hauksbee the Younger, 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 ofthe same naple with whom he is often confused (Hauksbee the Younger was also a member of the Royal Society) Hauksbee carried on the tradition of experimentation 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 StandardAT 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 Comcom-puter Interface standards
Trang 10cable construction.
HCShard 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 ofthe 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
HDCMSee high-resolution direct core monitoring
HDD See hard disk drive
HDLCSee High Level Data Link Control
HDSLSee high bit-rate Digital Subscriber Line
HDTHost Digital Terminal
HDTVSee High Definition Television
headAdevice 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 thrashingIf 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 ifnot
terminated in time
header 1 Identifying text printed in a block at the
head of a file or document Header information
fre-quently includes file format, version, date ofcreation,
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 linkdur-ing System
windowing routines and graphics routines are
fre-quently linked in from header files Aheader 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-tocoI data unit
header areaIn an EDI file, the area that contains the
header information for the document See EDI,
header
Header Error ControlHEC In ATM transmissions,
an error detection mechanism contained in a byte at
the end ofthe 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
Some satellite service providers have compensated for this by developing a variety of solutions, includ-ing interleavinclud-ing ofcells to isolate the data from burst errors See ATM Link Enhancer
headsetA 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 memoryA 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 memorynee~ 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
heat sinkAstructure 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 CPUs 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 ofthe 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 a half 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 layerSee Kennelly-Heaviside layer
Heaviside, Oliver (1850-1925)AnEnglish 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 withJ J Thompson, Heaviside theorized about the electromagnetic reactions and mass ofelec-trically charged particles in motion See Kennelly-Heaviside layer, Maxwell's equations