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Glossary 153
NVRAM — Nonvolatile random-access memory. Memory
that does not lose its contents when you turn off your
system. NVRAM is used for maintaining the date, time,
and system configuration information.
parity — Redundant information that is associated with a
block of data.
partition — You can divide a hard drive into multiple
physical sections called partitions with the fdisk
command. Each partition can contain multiple logical
drives. You must format each logical drive with the format
command.
PCI — Peripheral Component Interconnect. A standard
for local-bus implementation.
PDU — Power distribution unit. A power source with
multiple power outlets that provides electrical power to
servers and storage systems in a rack.
peripheral — An internal or external device, such as a
diskette drive or keyboard, connected to a system.
PGA — Pin grid array. A type of processor socket that
allows you to remove the processor chip.
pixel — A single point on a video display. Pixels are
arranged in rows and columns to create an image. A video
resolution, such as 640 x 480, is expressed as the number
of pixels across by the number of pixels up and down.
POST — Power-on self-test. Before the operating system
loads when you turn on your system, the POST tests
various system components such as RAM and hard drives.
processor — The primary computational chip inside the
system that controls the interpretation and execution of
arithmetic and logic functions. Software written for one
processor must usually be revised to run on another
processor. CPU is a synonym for processor.
protected mode — An operating mode that allows
operating systems to implement:
• A memory address space of 16 MB to 4 GB
• Multitasking
• Virtual memory, a method for increasing addressable
memory by using the hard drive
The Windows 2000 and UNIX 32-bit operating systems
run in protected mode. MS-DOS cannot run in protected
mode.
PS/2 — Personal System/2.
PXE — Preboot eXecution Environment. A way of
booting a system via a LAN (without a hard drive or
bootable diskette).
RAC — Remote access controller.
RAID — Redundant array of independent disks. A
method of providing data redundancy. Some common
implementations of RAID include RAID 0, RAID 1,
RAID 5, RAID 10, and RAID 50. See also guarding,
mirroring, and striping.
RAM — Random-access memory. The system’s primary
temporary storage area for program instructions and data.
Any information stored in RAM is lost when you turn off
your system.
RAS — Remote Access Service. This service allows users
running the Windows operating system to remotely access
a network from their system using a modem.
readme file — A text file, usually shipped with software or
hardware, that contains information supplementing or
updating the product’s documentation.
read-only file — A read-only file is one that you are
prohibited from editing or deleting.
ROM — Read-only memory. Your system contains some
programs essential to its operation in ROM code. A ROM
chip retains its contents even after you turn off your
system. Examples of code in ROM include the program
that initiates your system’s boot routine and the POST.