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parity checking A way to verify
the accuracy of data transmitted
over the SCSI bus. One bit in the
transfer is used to make the sum of
all the 1 bits either odd or even (for
odd or even parity). If the sum is
not correct, an error message
appears. SCSI uses odd parity.
PCI (peripheral component
interconnect) A local bus
specification that allows
connection of integrated peripheral
controller components, peripheral
add-in boards, and
processor/memory systems. It
bypasses the slower ISA and EISA
busses.
peripheral devices A hardware
device (such as a video monitor,
disk drive, printer, or CD-ROM)
used with a computer and under
the computer’s control. SCSI
peripherals are controlled through
a SCSI host adapter.
pin-1 orientation The alignment
of pin 1 on a SCSI cable connector
and the pin 1 position on the SCSI
connector into which it is inserted.
External SCSI cables are keyed to
ensure proper alignment, but
internal SCSI ribbon cables may
not be.
PIO (programmed
input/output) A way the CPU can
transfer data to and from memory
via the computer’s I/O ports. PIO
can be faster than DMA, but
requires CPU time.
port address Also Port Number.
The address through which
commands are sent to a host
adapter board. This address is
assigned by the PCI bus.
port number See port address.
queue tags A way to keep track of
multiple commands while allowing
increased throughput on the SCSI
bus.
RAM (Random Access
Memory) Generally, the
computer’s primary working
memory in which program
instructions and data are stored
and are accessible to the CPU.
Information can be written to and
read from RAM. The contents of
RAM are lost when the computer is
turned off.
RISC core Symbios SCSI chips
contain a RISC (Reduced
Instruction Set Computer)
processor, programmed through
microcode scripts.
ROM (Read-Only Memory)
Memory from which information
can be read but not changed. The
contents of ROM are not erased
when the computer is turned off.
SCAM (SCSI Configured
AutoMatically) A method to
automatically allocate SCSI IDs
via software when SCAM
compliant SCSI devices are
attached.