Installing and Administering HP EISA FDDI/9000 and HP HSC FDDI/9000

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Glossary
CPU (Central Processing Unit)
A computer’s main microprocessor
chip.
CRC (Cyclic Redundancy
Check) An error checking
procedure in which bytes at the end
of a frame are used by the receiving
node to detect a transmission
problem.
D
DAC (Dual Attachment
Concentrator A concentrator that
offers two connections to the FDDI
network capable of accommodating
the FDDI dual (counter-rotating)
ring, and additional ports for the
connection of other concentrators or
FDDI stations.
DAS (Dual Attachment
Station) An FDDI station that
offers two connections to the FDDI
dual counter-rotating ring.
Differential Manchester
encoding A signaling method that
encodes clock and data information
into bit symbols. Each bit symbol is
divided into two halves, where the
second half is the inverse of the first
half. A zero is represented by a
polarity change at the start of the bit
time; a one is represented by no
polarity change at the start of the bit
time.
DMA (Direct Memory Access)
A fast method of moving data
between two processor subsystems
without processor intervention.
DMA Controller Provides control
of the larger part of the system’s
DMA (Direct Memory Access)
facility. The DMA controller
responds to requests from the DMA
device and provides address and
control signals to the memory slaves
and DMA device.
DMA Device The DMA device is
typically located on a peripheral
board on the EISA or ISA bus. The
DMA device initiates DMA
transfers, which are controlled by
signals generated by the system
DMA controller. The DMA device
either presents or receives data
during a DMA transfer and uses
several signals to inform the DMA
controller of the staus of the transfer.