Page 239 - Electrical Engineering Dictionary

dynamic load line graphical plot showing be read or written through the “access tran-
the instantaneous relationship between volt- sistor” in the cell. Since the charge will
age across and current through a transistor slowly leak away (through semiconductor
when driven by an input AC signal. junctions), the cells need to be “refreshed”
once every few milliseconds. This is typi-
dynamic matching See variational cally done using on-chip circuitry. DRAMs
similarity. have very high storage density, but are slower
than SRAMs (static RAMs). See also burst
dynamic memory allocation the run- refresh, distributed refresh.
time assignment of small units of memory to
an active program. Used typically to support dynamic range refersto therangeofinput
growing structures such as lists. signal amplitudes over which an electronic
device will operate within a set of specified
dynamic path reconnect used in IBM’s parameters. Usually expressed in decibels.
high-end computer systems to allow a “sub- In a communications receiver, the upper end
channel” to change its channel path each time of the dynamic range is determined by the
it cycles through a disconnect/reconnect with largest tolerable input signal, while the lower
a given device. This enables it to be assigned end is set by the receiver’s sensitivity. The
to another available path, rather than just wait sensitivity is the minimum discernible signal
for the currently allocated path to become for a specific signal-to-noise ratio (SNR). See
free. also signal-to-noise ratio.

dynamic programming introduced by dynamic reconfiguration changes of op-
Bellman, one of the best known methods for tical paths from sources to detectors which
solving the optimal control problems. A re- are instantly controllable. Paths of optical
cursive method to compute the optimal con- signals are controlled and changed by an op-
trol as a function of the state, dynamic pro- tical crossbar switch that is usually a spatial
gramming is used in multistage systems by light modulator.
working backward from the final stage.
Dynamic programming is based on The dynamic scattering procedure to study
Optimality Principle. The Principle says that the change of state of atoms and molecules by
optimal control strategy has the feature that analyzingthefrequencyshiftandfluctuations
regardless of initial state and initial decision, of scattered light.
decision in the next step must form an opti-
mal control strategy with respect to the final dynamic scheduling (1) creating the ex-
state of the previous decisions. This principle ecution schedule of instructions at run-time
allows us to find an optimal strategy in a nu- by the hardware, which provides a different
merical way. The principle serves to limit the schedulethanstrictprogramorder(i.e., apro-
number of potentially optimal control strate- cessor issues instructions to functional units
gies that must be investigated. It also implies out of program order). The processor can dy-
that optimal control strategies must be deter- namically issue an instruction as soon as all
mined by working backward from the final its operands are available and the required ex-
stage. ecution unit is not busy. Thus, an instruction
is not delayed by a stalled previous instruc-
dynamic random access memory (DRAM) tion unless it needs the results of that previous
a semiconductor memory using one capac- instruction.
itor and one access transistor per cell (bit). (2) changing the software program sched-
The information is stored dynamically on a ule dynamically depending on data or oper-
small charge on the cell capacitance, and can ating conditions.

c
2000 by CRC Press LLC