APA-1460 SlimSCSI Technical Reference
Glossary-4
APA-1460 SlimSCSI Technical Reference
Stock Number: 510671-00 Rev. A
Page: -4
Print Spec Number: 492966-00
Current Date: 8/22/94
ECN Date: 8/30/94
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P
PAL
Programmable Array Logic. Programmable
logic elements used for decoding and con-
trol functions.
Parity Checking
A SCSI feature used to verify whether data
has been transmitted correctly over the
SCSI bus. A check bit is added to each byte
of data to make the sum of all the 1 bits
either odd or even, depending on the pro-
tocol. If the sum of the bits is even when it
should be odd, or vice-versa, data has been
corrupted and an error message appears.
PC
-
AT
A family of small computers sold by IBM,
also called the Personal Computer-AT fam-
ily of computers. The name is trademarked
by IBM.
PCMCIA
Personal Computer Memory Card Interna-
tional Association. A widely accepted
industry standard for small form factor
add-in cards. Such add-in cards generally
fall into two categories: memory add-in
products and I/O add-in products.
Peripheral Device
Any optional input or output device, such
as a printer or CD-ROM drive, that con-
nects to a computer’s CPU. For SCSI
peripherals this connection is made via the
SCSI bus.
PIO
See Programmed Input/Output.
Plug and Play
A hardware and software mechanism that
provides an automatic way for the system
to self configure and optimally allocate sys-
tem resources such as memory, I/O ports,
IRQ, and DMA channels between Plug and
Play cards and other devices in the system.
Port Address
Or I/O Port Address. A window through
which software programs send commands
to the host adapter board.
Programmed Input/Output
A method of data transfer in which the host
microprocessor transfers data to and from
memory. PIO enables very fast data transfer
rates, especially in single-tasking operating
systems like DOS.
R
RAM
Random Access Memory. Memory of
which any byte can be accessed directly in a
single memory cycle. Information can be
read from and written to the memory.
ROM
Read-Only Memory. Memory in which any
byte can be read but not written.
S
SCSI
Small Computer Systems Interface. A bus
interface standard that defines physical and
electrical characteristics for hardware
devices. (The original SCSI standard is
sometimes called SCSI-1.) SCSI provides a
standard interface that enables many differ-
ent kinds of devices, such as disk drives,
magneto-optical disks, CD-ROM drives,
and tape drives to interface with the host
computer.
SCSI
-
2
A computer bus interface standard that
adds features to the SCSI-1 standard.
Included among these features are 32-bit
data transfer, command queuing, Fast SCSI,
and support for a wider variety of periph-
eral devices.
SCSI Bus
One or more SCSI peripheral devices and a
host adapter, connected by cables in a
daisy-chain configuration. The bus may
include both internal and external SCSI
devices. In a computer with two or more
host adapters, each adapter has its own
separate SCSI bus.
SCSI Device
A device such as a host adapter, hard disk
drive, or CD-ROM drive that conforms to
the SCSI interface standard and is attached
