Page 338 - Electrical Engineering Dictionary

hard magnetic material a ferromagnetic hardware noise radio frequency emis-
material that retains its magnetization when sions due to arcing of utility lines at defective
the magnetizing field is removed; a magnetic connectors.
material with significant coercivity.
harmonic (1) the name associated with a
number used to denote the frequency com-
hard real-time See hard real-time system.
ponents that exist in a certain fourier series
representation for a certain function of time
f(t). The Fourier series representation is
hard real-time system a real-time system given
in which missing even one deadline results in
∞
system failure. Compare with soft real-time, X
f(t) = F n ∗[cos (nω o t) + j sin (nω o t)]
firm real-time.
n=−∞
hard X-ray having sufficient photon en- where n = 0, 1, 2, 3,..., ω o = 2π/T , j =
√
ergy to penetrate “hard” material; usually −1, T is the period of the function f(t),
more than about 15 keV. F n is the coefficient of the Fourier series for
a certain value of n:
1st harmonic has F n = F 1 and
hard-decision decoding decoding of en-
coded information given symbol decisions [cos (1ω 0 t) + j sin (1ω 0 t)]
of the individually coded message symbols.
Compare with soft-decision decoding. 2nd harmonic has F n = F 2 and

[cos (2ω 0 t) + j sin (2ω 0 t)]
hardware computer constructs that have
a physical manifestation.
3rd harmonic has F n = F 3 and
[cos (3ω 0 t) + j sin (3ω 0 t)]
hardware accelerator a piece of hard-
ware dedicated to performing a particu-
etc.
lar function (such as image convolution or
(2) sinusoidal component of a periodic
matrix-vector products) which would other-
waveform that has a frequency equal to an
wise be performed in software. Although
integer multiple of the basic frequency (or
much less flexible, dedicated hardware im-
fundamental frequency). Thus the third har-
plementations can give significant speed im-
monic of a power system voltage in the U.S.
provements over software, and are especially
hasafrequencyof3×60, or180Hz. Forelec-
useful for real-time applications.
tric systems powered by sinusoidal sources,
harmonics are introduced by nonlinear de-
vices such as saturated iron cores and power
hardware interrupt an interrupt gener- electronic devices.
ated by a hardware device, for example, key-
board, the DMA, PIC, the serial adapter, the harmonic amplifier a type of amplifier
printer adapter, etc. Other hardware inter- that utilizes various forms of harmonic and
rupts can be generated by the control unit or mixing actions. These amplifiers may pump
by the ALU, for example, for the presence of up the fundamental by increasing the switch-
a division per zero, for attempting to execute ing efficiency of the active device. Others
an unknown instruction. This last class of mayactuallybeusedasfrequencymultipliers
hardware interrupts is called internal excep- or frequency converters (mixers). All class
tion. F, G, and H amplifiers fit into this general

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