Specifications

Glossary
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PLCC (plastic leaded-chip carrier) A chip-
carrier package with J-leads around the perimeter of
the package.
Plug and Play (PnP) A hardware and software
specification developed by Intel that enables a PnP
system and PnP adapter cards to automatically con-
figure themselves. PnP cards are free from switches
and jumpers and are configured via the PnP BIOS
in the host system, or via supplied programs for
non-PnP systems. PnP also allows the system to
detect and configure external devices, such as mon-
itors, modems, and devices attached to USB or
IEEE-1394 ports. Windows 9x and later support PnP
devices.
polling A communications technique that deter-
mines when a device is ready to send data. The sys-
tem continually interrogates polled devices in a
round-robin sequence. If a device has data to send,
it sends back an acknowledgment and the transmis-
sion begins. This contrasts with interrupt-driven
communications, in which the device generates a
signal to interrupt the system when it has data to
send. Polling enables two devices that would nor-
mally have an IRQ conflict to coexist because the
IRQ is not used for flow control.
port A plug or socket that enables an external
device, such as a printer, to be attached to the
adapter card in the computer. Also a logical address
used by a microprocessor for communication
between it and various devices.
port address One of a system of addresses used
by the computer to access devices such as disk
drives or printer ports. You might need to specify
an unused port address when installing any adapter
boards in a system unit.
port replicator For mobile computers, a device
that plugs into the laptop and provides all the ports
for connecting external devices. The advantage of
using a port replicator is that the external devices
can be left connected to the replicator and the
mobile computer can be connected to them all at
once by connecting to the replicator, rather than
connecting to each individual device. A port repli-
cator differs from a docking station in that the
latter can provide additional drive bays and expan-
sion slots not found in port replicators.
Traditionally, port replicators have plugged into a
proprietary bus on the rear of a portable computer,
but so-called universal models might attach to the
PC Card (PCMCIA) slot or to a USB port.
portable computer A computer system smaller
than a transportable system but larger than a lap-
top system. Very few systems in this form factor are
sold today, but companies such as Dolch still pro-
duce them. Most portable systems conform to the
lunchbox style popularized by Compaq or the
briefcase style popularized by IBM, each with a
fold-down (removable) keyboard and built-in dis-
play. These systems characteristically run on AC
power and not on batteries, include several expan-
sion slots, and can be as powerful as full desktop
systems.
POS (Programmable Option Select) The
Micro Channel Architecture’s POS eliminates
switches and jumpers from the system board and
adapters by replacing them with programmable reg-
isters. Automatic configuration routines store the
POS data in a battery-powered CMOS memory for
system configuration and operations. The configu-
ration utilities rely on adapter description files
(ADF) that contain the setup data for each card.
POST (power-on self test) A series of tests run
by the computer at power-on. Most computers scan
and test many of their circuits and sound a beep
from the internal speaker if this initial test indi-
cates proper system performance.
PostScript A page-description language devel-
oped primarily by John Warnock of Adobe Systems
for converting and moving data to the laser-printed
page. Instead of using the standard method of
transmitting graphics or character information to a
printer and telling it where to place dots one by
one on a page, PostScript provides a way for the
laser printer to interpret mathematically a full page
of shapes and curves. Adobe Acrobat converts
PostScript output files into files that can be read by
users with varying operating systems. See also
Acrobat.
POTS (plain old telephone service) Standard
analog telephone service.
power factor conversion (PFC) An expression
of how efficient a power supply or UPS is at provid-
ing power. A device that provides 100% of its rated
Appendix A
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