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174 Glossary
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.
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.
PSU — Power supply unit.
PXE — Preboot eXecution Environment. A way of booting a system via a LAN
(without a hard drive or bootable diskette).
QPI— QuickPath Interconnect. The bus interface between the processors and
between the processors and the IOH chip.
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, RAID 50, and RAID 60. See also 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.
RDIMM — A registered DDR3 memory module.
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.
ROMB — RAID on motherboard.
SAN — Storage Area Network. A network architecture that enables remote network-
attached storage devices to appear to a server to be locally attached.