Specifications

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Appendix A Glossary
passive heatsink A heatsink that does not
include a fan. Passive heatsinks used on processors
are usually larger than active heatsinks and rely on
case fans to dissipate heat. Many North Bridge or
memory control hubs on recent motherboards also
use passive heatsinks.
passive matrix Another name for dual-scan,
display-type LCDs.
PC Card (PCMCIA—Personal Computer
Memory Card International Association)
A credit card–sized expansion adapter for
notebook and laptop PCs. PC Card is the official
PCMCIA trademark; however, both PC Card
and PCMCIA card are used to refer to these stan-
dards. PCMCIA cards are removable modules that
can hold numerous types of devices, including
memory, modems, fax/modems, radio transceivers,
network adapters, solid state disks, hard disks, and
flash memory adapters.
PCI (Peripheral Component Interconnect)
A standard bus specification initially developed by
Intel in 1992 that bypasses the standard ISA I/O
bus and uses the system bus to increase the bus
clock speed and take full advantage of the CPU’s
data path. The most common form of PCI is 32 bits
wide running at 33MHz, but 66MHz and 64-bit
wide versions of PCI are frequently used on servers.
PCI Express A high-speed serial I/O intercon-
nect standard being developed by the PCI-SIG
(www.pcisig.com) as an eventual replacement for
the original PCI standard. The initial version of PCI
Express supports 0.8V signaling at 2.5GHz, while
version 2 and later support 5GHz, allowing for
250MBps or 500MBps bandwidth per lane, respec-
tively. Connectors featuring 1, 2, 4, 8, and 16 lanes
are used in PCs, with up to 32 lanes possible.
PCI-X (Peripheral Component Interconnect
Extended) A faster 64-bit version of PCI
with speeds up to 133MHz. PCI-X is backward-
compatible with PCI but also supports fault-
tolerant features such as automatic reinitializing
and disabling of faulty add-on cards.
PCL (Printer Control Language) Developed
by Hewlett-Packard in 1984 as a language for the
HP LaserJet printer. PCL is now the de facto indus-
try standard for PC printing. PCL defines a standard
set of commands, enabling applications to commu-
nicate with HP or HP-compatible printers and is
supported by virtually all printer manufacturers.
Various levels of PCL are supported by HP and
other brands of laser and inkjet printers.
PCM (pulse code modulation) A technique
for digitizing analog signals by sampling the signal
and converting each sample into a binary number.
Also stands for powertrain control module, which
is what the computer in most modern automobiles
is called.
PDA (personal digital assistant) A handheld,
palm-sized computer that functions primarily as a
personal organizer and can be combined with a cel-
lular phone or pager. Leading examples include the
Palm series, Windows–based PalmPCs, and the
Handspring (which also runs the Palm OS).
PDF (portable document format) Files with
this extension can be read with the Adobe Acrobat
Reader. See also Acrobat.
pedestal A server chassis that resembles a tower
chassis but is wider, taller, and deeper to permit the
use of larger motherboards. Some pedestal server
chassis include wheels, and some can be converted
to a rack-mount form factor.
peer-to-peer A type of network in which any
computer can act as both a server (by providing
access to its resources to other computers) and a
client (by accessing shared resources from other
computers).
pel See pixel.
Pentium An Intel microprocessor with 32-bit
registers, a 64-bit data bus, and a 32-bit address bus.
The Pentium has a built-in L1 cache segmented
into a separate 8KB cache for code and another 8KB
cache for data. The Pentium includes an FPU or
math coprocessor. It is backward compatible with
the 486 and can operate in real, protected virtual,
and virtual real modes. The MMX Pentium has a
16KB cache for code, has a 16KB cache for data,
and adds the MMX instruction set.
Pentium 4 The first Intel seventh-generation
processor, it’s based on a new 32-bit microarchitec-
ture that operates at higher clock speeds because of
hyper pipelined technology, a rapid execution
engine, a 400MHz system bus (later boosted to
533MHz and 800MHz), and an execution trace
cache. The system bus runs at four times the
processor bus speed. The floating-point and
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