Specifications

Glossary
53
overlay Part of a program loaded into memory
only when it is required.
overrun A situation in which data moves from
one device more quickly than a second device can
accept it.
overscanning A technique used in consumer
display products that extends the deflection of a
CRT’s electron beam beyond the physical bound-
aries of the screen to ensure that images always fill
the display area.
overwrite To write data on top of existing data,
thus erasing the existing data.
package A device that includes a chip mounted
on and sealed inside a carrier.
packet A message sent over a network that con-
tains data and a destination address.
packet writing A recording technique that
sends data to a CD-R or CD-RW disc in multiple
blocks, enabling normal writing processes in
Windows Explorer to be used instead of a CD-
mastering program. Compatible packet-reading
software, such as Roxio’s UDF Reader for DirectCD,
must be used on systems that don’t have a CD-R or
CD-RW drive to enable the media to be read. See
also Mt. Rainier.
pairing Combining processor instructions for
optimal execution on superscalar processors.
PAL 1) Phase Alternating Line system. Invented
in 1961, a system of TV broadcasting used in
England and other European countries (except
France). PAL’s image format is 4:3, 625 lines, 50Hz,
and 4MHz video bandwidth with a total 8MHz of
video channel width. With its 625-line picture
delivered at 25 frames per second, PAL provides a
better image and an improved color transmission
over the NTSC system used in North America. As a
consequence, PAL and NTSC video tapes aren’t
interchangeable. 2) Programmable array logic, a
type of chip that has logic gates specified by a
device programmer.
palmtop computer A computer system smaller
than a notebook that is designed so it can be held
in one hand while being operated by the other.
Many are now called PDAs or personal digital
assistants.
parallel A method of transferring data characters
in which the bits travel down parallel electrical
paths simultaneously—for example, eight paths for
8-bit characters. Data is stored in computers in par-
allel form but can be converted to serial form for
certain operations.
parity A method of error checking in which an
extra bit is sent to the receiving device to indicate
whether an even or odd number of binary 1 bits
was transmitted. The receiving unit compares the
received information with this bit and can obtain a
reasonable judgment about the validity of the char-
acter. The same type of parity (even or odd) must
be used by two communicating computers, or both
may omit parity. When parity is used, a parity bit is
added to each transmitted character. The bit’s value
is 0 or 1, to make the total number of 1s in the
character even or odd, depending on which type of
parity is used. Parity checking isn’t widely sup-
ported on recent systems, but memory with parity
bits can be used as ECC memory on systems with
ECC-compatible chipsets. See also ECC.
park program A program that executes a seek
to the highest cylinder or just past the highest
cylinder of a drive so the potential of data loss is
minimized if the drive is moved. Park programs are
not interchangeable between drives and are no
longer required on most drives 40MB and above
because these drives self-park their heads for safety.
partition A section of a hard disk devoted to a
particular operating system. Most hard disks have
only one partition, devoted to DOS. A hard disk
can have as many as four partitions, each occupied
by a different operating system. DOS v3.3 or later
can occupy two of these four partitions. A boot
manager enables you to select the partition occu-
pied by the operating system you want to start if
you have multiple operating systems installed in
different partitions. See also boot manager.
Pascal A high-level programming language
named for the French mathematician Blaise Pascal
(1623–1662). Developed in the early 1970s by
Niklaus Wirth for teaching programming and
designed to support the concepts of structured pro-
gramming.
Appendix A
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