accessed. The page table may itself be stored
in standard memory or may be stored within a
special type of memory known as associative
memory. A page table stored in associative
memory is known as a translation lookaside
buffer.
page-fault-frequency replacement
a re-
placement algorithm for pages in main mem-
ory. This is the reciprocal of the time between
successive page faults. Replacement is ac-
cording to whether the page-fault frequency
is above or below some threshold.
page-mode DRAM
a technique that uses
a buffer like a static RAM; by changing the
column address, random bits can be accessed
in the buffer until the next row access or re-
fresh time occurs.
This organization is typically used in
DRAM for column access. Additional tim-
ing signals allow repeated accesses to the
buffer without a row-access time. See also
two-dimensional memory organization
.
page-printing printer
a human-readable
output device used for producing documents
in a written form. The printer stores a whole
page in memory before printing it (e.g., a
laser printer).
paged segmentation
the combination of
paging and segmentation in which segments
are divided into equal sized pages. Allows
individual pages of a segment rather than the
whole segment to be transferred into and out
of the main memory.
paged-segment
a segment partitioned
into an integral number of pages.
paging
the process of transferring pages
between main memory and secondary mem-
ory.
paging channel
a channel in a wireless
communication system used to send paging
messages.
Paging messages are typically
used to set up telephone calls and also to
send control messages to terminals that are
involved in a communication session.
Pagourek–Witsenhausen paradox
the
best known result concerning comparison of
performance sensitivity between open-loop
and closed-loop nominally optimal systems.
The result provides the somewhat deceptive
answer to a question of what is the devia-
tion of the performance index for a closed-
loop and open-loop implementations of nom-
inally optimal control systems due to param-
eter deviations from its nominal value (for
which the optimal control has been calcu-
lated). The answer considered either obvi-
ous or paradoxical can be expressed as fol-
lows: the infinitesimal sensitivity of the per-
formance index expressed by its first varia-
tion caused by a variation of the parameter
vector is the same whether an open-loop or
a closed-loop implementation of the nomi-
nally optimal control is used. The result pri-
mary found for linear-quadratic problem has
been generalized for nonlinear time-varying
sufficiently smooth optimal control problems
with free terminal state.
PAL
See
phase alternate line
or
program-
mable array logic
.
PAM
See
pulse amplitude modulation
.
PAM system
See
prism
| air | metal
system
.
panelboard
an assembly of one or more
panel units containing power buses, auto-
matic overcurrent protective devices, that is
placed in a cabinet or cutout box located in
or flush on a wall. The assembly can only
be accessed from the front and may contain
switches for operation of light, heat, or power
circuits. See
switchboard
.
pantograph
an apparatus for applying
sliding contacts to the power lines above an
electric railroad locomotive.
c
2000 by CRC Press LLC