Page 268 - Electrical Engineering Dictionary

is as follows: ory included into the 640 kb to seen up to
8 Mb of memory divided into pages of 16 kb.
XY X ⊕ Y
To this end, special memory boards were
FF F built. Currently, the MS-DOS is still limited
FT T to 640 kb, but the new microprocessors can
TF T address even several gigabytes over the first
TT F megabyte. Thus, to maintain the compatibil-
ity with the previous version and the adoption
of the MS-DOS, the presence of expanded
exclusive reads and exclusive writes
memory is simulated by means of specific
(EREW) shared memory model, in which
drivers.
only exclusive reads and exclusive writes are
allowed.
expectation the integral of a function with
execution cycle sequence of operations respect to some probability measure. If f(·)
necessary to execute an instruction. is a deterministic function and x is random,
governed by probability density p(x), then
execution time amount of time it takes
Z ∞
a computation (whether an instruction or an
E[f(x)]= f(x)p(x)dx.
entire program) to complete, from beginning
−∞
to end. Time during which an instruction or a
program is executed. The portion of one ma-
chine cycle needed by a CPU’s supervisory-
expected value of a random variable en-
control unit to execute an instruction.
semble average value of a random variable
that is given by integrating the random vari-
execution unit in modern CPU imple-
able after scaling by its probability density
mentations, the module in which actual in-
function (weighted average) over the entire
struction execution takes place. There may
range.
be a number of execution units of different
types within a single CPU, including inte-
expert system a computer program that
ger processing units, floating point process-
emulates a human expert in a well-bounded
ing units, load/store units, and branch pro-
domain of knowledge.
cessing units.
exhaustive search a search through all explicit value a value associated with the
possibilities before deciding on what action bit string according to the rule defined by the
to take. For example, for the maximum- number representation system being used.
likelihood (exhaustive search) detection of
k
a sequence of k bits, all 2 possible bit se- explosion-proof machine National Elec-
quences are considered and the one with the trical Manufacturers Association (NEMA)
largest likelihood is selected. classification describing an electrical ma-
chine that is totally enclosed and whose en-
expanded memory expanded memory closure is designed to withstand an internal
specification, EMS, was born for adding explosion of a specified gas or vapor that may
memory to PCs (the so-called LIM-EMS). accumulate within the enclosure. The speci-
PCs were limited in memory to 640 kb even fication also requires that the design prevent
if the 8088/8086 CPU’s limit is 1 Mb. Thus, ignition of the specified gas or vapor sur-
in order to overcome this limit, the additional rounding the enclosure due to sparks, flashes,
memory was added by using a paging mech- or explosions of the specified gas within the
anism: up to four windows of 16 kb of mem- enclosure.

c
2000 by CRC Press LLC