Adaptec AHA-2740W User Manual page 113

configuration. The bus may
include both internal and exter-
nal SCSI devices. In systems that
have more than one host
adapter, each adapter has its
own separate SCSI bus.
SCSI Device
A device such as a host adapter
board, fixed disk drive, or CD-
ROM drive that conforms to the
SCSI interface standard and is
attached to a SCSI bus cable. The
device may be an initiator, a tar-
get, or capable of both types of
operation.
SCSI ID
An identifier assigned to SCSI
devices that enables them to
communicate with a computer
when they are attached to a host
adapter via the SCSI bus. Each
SCSI host adapter board has 8
available SCSI IDs with the
numbers 0 through 7. Usually
the host adapter itself is
assigned SCSI ID 7, and fixed
disk devices are assigned to
SCSI IDs 0 and 1.
Single-ended
A term referring to the electrical
characteristics of the signals
used on the SCSI bus interface.
Single-ended signals occupy a
single conductor and are refer-
ences to a common ground car-
ried on the cable between the
SCSI components attached. Most
SCSI devices use single-ended
grounding.
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AHA-2740W/2742W/2744W User's Guide
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Some SCSI devices use a differen-
tial grounding scheme. These
devices are not supported by the
AHA-2740W/2742W. Differen-
tial devices may be damaged if
you connect them and the
AHA-2740W/2742W to the
same SCSI bus.
Single-threaded Operation
Operation of the computer sys-
tem such that only one program
can be operating or active at a
time. The system must wait until
all resources are available before
starting an operation, and it can-
not start another operation until
the first one is completed.
Small Computer Systems Interface
See SCSI.
Synchronous Data Transfer
A method of data transfer in
which data on the SCSI bus is
clocked with fixed-length, fixed-
frequency strobe pulses. The
acknowledgments may be
delayed several clock periods
from the data requests. Synchro-
nous data transfer can be used
only for data transmission on
the SCSI bus. It cannot be used
for command, message, and sta-
tus transmission.
Synchronous Data Transfer Negotiation
The message exchange between
the initiator and the target that
allows the negotiation of the
data transfer frequency and
delay between requests and
acknowledgments required for
synchronous data transfer. Once
Page: Glossary-7
ECN Date: 8/9/94
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